Release version 3.3 RC1 (2021.1.0).

See #3829

.github/workflows/project.yml

@@ -36,7 +36,7 @@ jobs:
           token: ${{ secrets.GH_ISSUES_TOKEN_SPRING_DATA }}
   Feedback-Provided:
     runs-on: ubuntu-latest
-    if: github.repository_owner == 'spring-projects' && github.event.action == 'created' && contains(join(github.event.issue.labels.*.name, ', '), 'waiting-for-feedback')
+    if: github.repository_owner == 'spring-projects' && github.event_name == 'issue_comment' && github.event.action == 'created' && github.actor != 'spring-projects-issues' && github.event.pull_request == null && github.event.issue.state == 'open' && contains(toJSON(github.event.issue.labels), 'waiting-for-feedback')
     steps:
       - name: Update Project Card
         uses: peter-evans/create-or-update-project-card@v1.1.2

.mvn/wrapper/maven-wrapper.properties

@@ -1 +1,2 @@
-distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.5.4/apache-maven-3.5.4-bin.zip
+#Mon Oct 11 14:30:24 CEST 2021
+distributionUrl=https\://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.8.3/apache-maven-3.8.3-bin.zip

CI.adoc

@@ -1,6 +1,6 @@
 = Continuous Integration
 
-image:https://jenkins.spring.io/buildStatus/icon?job=spring-data-mongodb%2Fmaster&subject=Moore%20(master)[link=https://jenkins.spring.io/view/SpringData/job/spring-data-mongodb/]
+image:https://jenkins.spring.io/buildStatus/icon?job=spring-data-mongodb%2Fmain&subject=Moore%20(main)[link=https://jenkins.spring.io/view/SpringData/job/spring-data-mongodb/]
 image:https://jenkins.spring.io/buildStatus/icon?job=spring-data-mongodb%2F2.1.x&subject=Lovelace%20(2.1.x)[link=https://jenkins.spring.io/view/SpringData/job/spring-data-mongodb/]
 image:https://jenkins.spring.io/buildStatus/icon?job=spring-data-mongodb%2F1.10.x&subject=Ingalls%20(1.10.x)[link=https://jenkins.spring.io/view/SpringData/job/spring-data-mongodb/]
 

CONTRIBUTING.adoc

@@ -1,3 +1,3 @@
 = Spring Data contribution guidelines
 
-You find the contribution guidelines for Spring Data projects https://github.com/spring-projects/spring-data-build/blob/master/CONTRIBUTING.adoc[here].
+You find the contribution guidelines for Spring Data projects https://github.com/spring-projects/spring-data-build/blob/main/CONTRIBUTING.adoc[here].

Jenkinsfile

@@ -3,7 +3,7 @@ pipeline {
 
 	triggers {
 		pollSCM 'H/10 * * * *'
-		upstream(upstreamProjects: "spring-data-commons/master", threshold: hudson.model.Result.SUCCESS)
+		upstream(upstreamProjects: "spring-data-commons/main", threshold: hudson.model.Result.SUCCESS)
 	}
 
 	options {
@@ -14,6 +14,22 @@ pipeline {
 	stages {
 		stage("Docker images") {
 			parallel {
+			    stage('Publish JDK 8 + MongoDB 5.0') {
+					when {
+						changeset "ci/openjdk8-mongodb-5.0/**"
+					}
+					agent { label 'data' }
+					options { timeout(time: 30, unit: 'MINUTES') }
+
+					steps {
+						script {
+							def image = docker.build("springci/spring-data-openjdk8-with-mongodb-5.0.0", "ci/openjdk8-mongodb-5.0/")
+								docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
+									image.push()
+								}
+							}
+						}
+					}
 				stage('Publish JDK 8 + MongoDB 4.0') {
 					when {
 						changeset "ci/openjdk8-mongodb-4.0/**"
@@ -23,39 +39,39 @@ pipeline {
 
 					steps {
 						script {
-							def image = docker.build("springci/spring-data-openjdk8-with-mongodb-4.0", "ci/openjdk8-mongodb-4.0/")
+							def image = docker.build("springci/spring-data-openjdk8-with-mongodb-4.0.23", "ci/openjdk8-mongodb-4.0/")
 							docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
 								image.push()
 							}
 						}
 					}
 				}
-				stage('Publish JDK 8 + MongoDB 4.2') {
+				stage('Publish JDK 8 + MongoDB 4.4') {
 					when {
-						changeset "ci/openjdk8-mongodb-4.2/**"
+						changeset "ci/openjdk8-mongodb-4.4/**"
 					}
 					agent { label 'data' }
 					options { timeout(time: 30, unit: 'MINUTES') }
 
 					steps {
 						script {
-							def image = docker.build("springci/spring-data-openjdk8-with-mongodb-4.2.0", "ci/openjdk8-mongodb-4.2/")
+							def image = docker.build("springci/spring-data-openjdk8-with-mongodb-4.4.4", "ci/openjdk8-mongodb-4.4/")
 							docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
 								image.push()
 							}
 						}
 					}
 				}
-				stage('Publish JDK 15 + MongoDB 4.2') {
+				stage('Publish JDK 16 + MongoDB 4.4') {
 					when {
-						changeset "ci/openjdk15-mongodb-4.2/**"
+						changeset "ci/openjdk16-mongodb-4.4/**"
 					}
 					agent { label 'data' }
 					options { timeout(time: 30, unit: 'MINUTES') }
 
 					steps {
 						script {
-							def image = docker.build("springci/spring-data-openjdk15-with-mongodb-4.2.0", "ci/openjdk15-mongodb-4.2/")
+							def image = docker.build("springci/spring-data-openjdk16-with-mongodb-4.4.4", "ci/openjdk16-mongodb-4.4/")
 							docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
 								image.push()
 							}
@@ -67,8 +83,9 @@ pipeline {
 
 		stage("test: baseline (jdk8)") {
 			when {
+				beforeAgent(true)
 				anyOf {
-					branch 'master'
+					branch(pattern: "main|(\\d\\.\\d\\.x)", comparator: "REGEXP")
 					not { triggeredBy 'UpstreamCause' }
 				}
 			}
@@ -76,16 +93,19 @@ pipeline {
 				label 'data'
 			}
 			options { timeout(time: 30, unit: 'MINUTES') }
+			environment {
+				ARTIFACTORY = credentials('02bd1690-b54f-4c9f-819d-a77cb7a9822c')
+			}
 			steps {
 				script {
 					docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
-						docker.image('springci/spring-data-openjdk8-with-mongodb-4.2.0:latest').inside('-v $HOME:/tmp/jenkins-home') {
+						docker.image('springci/spring-data-openjdk8-with-mongodb-4.0.23:latest').inside('-v $HOME:/tmp/jenkins-home') {
 							sh 'mkdir -p /tmp/mongodb/db /tmp/mongodb/log'
 							sh 'mongod --setParameter transactionLifetimeLimitSeconds=90 --setParameter maxTransactionLockRequestTimeoutMillis=10000 --dbpath /tmp/mongodb/db --replSet rs0 --fork --logpath /tmp/mongodb/log/mongod.log &'
 							sh 'sleep 10'
 							sh 'mongo --eval "rs.initiate({_id: \'rs0\', members:[{_id: 0, host: \'127.0.0.1:27017\'}]});"'
 							sh 'sleep 15'
-							sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw clean dependency:list test -Duser.name=jenkins -Dsort -U -B'
+							sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml clean dependency:list test -Duser.name=jenkins -Dsort -U -B'
 						}
 					}
 				}
@@ -94,8 +114,9 @@ pipeline {
 
 		stage("Test other configurations") {
 			when {
+				beforeAgent(true)
 				allOf {
-					branch 'master'
+					branch(pattern: "main|(\\d\\.\\d\\.x)", comparator: "REGEXP")
 					not { triggeredBy 'UpstreamCause' }
 				}
 			}
@@ -105,58 +126,91 @@ pipeline {
 						label 'data'
 					}
 					options { timeout(time: 30, unit: 'MINUTES') }
+					environment {
+						ARTIFACTORY = credentials('02bd1690-b54f-4c9f-819d-a77cb7a9822c')
+					}
 					steps {
 						script {
 							docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
-								docker.image('springci/spring-data-openjdk8-with-mongodb-4.0:latest').inside('-v $HOME:/tmp/jenkins-home') {
+								docker.image('springci/spring-data-openjdk8-with-mongodb-4.0.23:latest').inside('-v $HOME:/tmp/jenkins-home') {
 									sh 'mkdir -p /tmp/mongodb/db /tmp/mongodb/log'
 									sh 'mongod --setParameter transactionLifetimeLimitSeconds=90 --setParameter maxTransactionLockRequestTimeoutMillis=10000 --dbpath /tmp/mongodb/db --replSet rs0 --fork --logpath /tmp/mongodb/log/mongod.log &'
 									sh 'sleep 10'
 									sh 'mongo --eval "rs.initiate({_id: \'rs0\', members:[{_id: 0, host: \'127.0.0.1:27017\'}]});"'
 									sh 'sleep 15'
-									sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw clean dependency:list test -Duser.name=jenkins -Dsort -U -B'
+									sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml clean dependency:list test -Duser.name=jenkins -Dsort -U -B'
 								}
 							}
 						}
 					}
 				}
 
-				stage("test: mongodb 4.2 (jdk8)") {
+				stage("test: mongodb 4.4 (jdk8)") {
 					agent {
 						label 'data'
 					}
 					options { timeout(time: 30, unit: 'MINUTES') }
+					environment {
+						ARTIFACTORY = credentials('02bd1690-b54f-4c9f-819d-a77cb7a9822c')
+					}
 					steps {
 						script {
 							docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
-								docker.image('springci/spring-data-openjdk8-with-mongodb-4.2.0:latest').inside('-v $HOME:/tmp/jenkins-home') {
+								docker.image('springci/spring-data-openjdk8-with-mongodb-4.4.4:latest').inside('-v $HOME:/tmp/jenkins-home') {
 									sh 'mkdir -p /tmp/mongodb/db /tmp/mongodb/log'
 									sh 'mongod --setParameter transactionLifetimeLimitSeconds=90 --setParameter maxTransactionLockRequestTimeoutMillis=10000 --dbpath /tmp/mongodb/db --replSet rs0 --fork --logpath /tmp/mongodb/log/mongod.log &'
 									sh 'sleep 10'
 									sh 'mongo --eval "rs.initiate({_id: \'rs0\', members:[{_id: 0, host: \'127.0.0.1:27017\'}]});"'
 									sh 'sleep 15'
-									sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw clean dependency:list test -Duser.name=jenkins -Dsort -U -B'
+									sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml clean dependency:list test -Duser.name=jenkins -Dsort -U -B'
 								}
 							}
 						}
 					}
 				}
 
-				stage("test: baseline (jdk15)") {
+				stage("test: mongodb 5.0 (jdk8)") {
+                	agent {
+                		label 'data'
+                	}
+                	options { timeout(time: 30, unit: 'MINUTES') }
+                	environment {
+                		ARTIFACTORY = credentials('02bd1690-b54f-4c9f-819d-a77cb7a9822c')
+                	}
+                	steps {
+                		script {
+                			docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
+                				docker.image('springci/spring-data-openjdk8-with-mongodb-5.0.0:latest').inside('-v $HOME:/tmp/jenkins-home') {
+                					sh 'mkdir -p /tmp/mongodb/db /tmp/mongodb/log'
+                					sh 'mongod --setParameter transactionLifetimeLimitSeconds=90 --setParameter maxTransactionLockRequestTimeoutMillis=10000 --dbpath /tmp/mongodb/db --replSet rs0 --fork --logpath /tmp/mongodb/log/mongod.log &'
+                					sh 'sleep 10'
+                					sh 'mongo --eval "rs.initiate({_id: \'rs0\', members:[{_id: 0, host: \'127.0.0.1:27017\'}]});"'
+                					sh 'sleep 15'
+                					sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml clean dependency:list test -Duser.name=jenkins -Dsort -U -B'
+                				}
+                			}
+                		}
+                	}
+                }
+
+				stage("test: baseline (jdk16)") {
 					agent {
 						label 'data'
 					}
 					options { timeout(time: 30, unit: 'MINUTES') }
+					environment {
+						ARTIFACTORY = credentials('02bd1690-b54f-4c9f-819d-a77cb7a9822c')
+					}
 					steps {
 						script {
 							docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
-								docker.image('springci/spring-data-openjdk15-with-mongodb-4.2.0:latest').inside('-v $HOME:/tmp/jenkins-home') {
+								docker.image('springci/spring-data-openjdk16-with-mongodb-4.4.4:latest').inside('-v $HOME:/tmp/jenkins-home') {
 									sh 'mkdir -p /tmp/mongodb/db /tmp/mongodb/log'
 									sh 'mongod --setParameter transactionLifetimeLimitSeconds=90 --setParameter maxTransactionLockRequestTimeoutMillis=10000 --dbpath /tmp/mongodb/db --replSet rs0 --fork --logpath /tmp/mongodb/log/mongod.log &'
 									sh 'sleep 10'
 									sh 'mongo --eval "rs.initiate({_id: \'rs0\', members:[{_id: 0, host: \'127.0.0.1:27017\'}]});"'
 									sh 'sleep 15'
-									sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -Pjava11 clean dependency:list test -Duser.name=jenkins -Dsort -U -B'
+									sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml -Pjava11 clean dependency:list test -Duser.name=jenkins -Dsort -U -B'
 								}
 							}
 						}
@@ -167,8 +221,9 @@ pipeline {
 
 		stage('Release to artifactory') {
 			when {
+				beforeAgent(true)
 				anyOf {
-					branch 'master'
+					branch(pattern: "main|(\\d\\.\\d\\.x)", comparator: "REGEXP")
 					not { triggeredBy 'UpstreamCause' }
 				}
 			}
@@ -185,7 +240,7 @@ pipeline {
 				script {
 					docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
 						docker.image('adoptopenjdk/openjdk8:latest').inside('-v $HOME:/tmp/jenkins-home') {
-							sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -Pci,artifactory ' +
+							sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -s settings.xml -Pci,artifactory ' +
 									'-Dartifactory.server=https://repo.spring.io ' +
 									"-Dartifactory.username=${ARTIFACTORY_USR} " +
 									"-Dartifactory.password=${ARTIFACTORY_PSW} " +
@@ -198,35 +253,6 @@ pipeline {
 				}
 			}
 		}
-
-		stage('Publish documentation') {
-			when {
-				branch 'master'
-			}
-			agent {
-				label 'data'
-			}
-			options { timeout(time: 20, unit: 'MINUTES') }
-
-			environment {
-				ARTIFACTORY = credentials('02bd1690-b54f-4c9f-819d-a77cb7a9822c')
-			}
-
-			steps {
-				script {
-					docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
-						docker.image('adoptopenjdk/openjdk8:latest').inside('-v $HOME:/tmp/jenkins-home') {
-							sh 'MAVEN_OPTS="-Duser.name=jenkins -Duser.home=/tmp/jenkins-home" ./mvnw -Pci,distribute ' +
-									'-Dartifactory.server=https://repo.spring.io ' +
-									"-Dartifactory.username=${ARTIFACTORY_USR} " +
-									"-Dartifactory.password=${ARTIFACTORY_PSW} " +
-									"-Dartifactory.distribution-repository=temp-private-local " +
-									'-Dmaven.test.skip=true clean deploy -U -B'
-						}
-					}
-				}
-			}
-		}
 	}
 
 	post {

LICENSE.txt

@@ -0,0 +1,202 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        https://www.apache.org/licenses/
+
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+
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+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "{}"
+      replaced with your own identifying information. (Don't include
+      the brackets!)  The text should be enclosed in the appropriate
+      comment syntax for the file format. We also recommend that a
+      file or class name and description of purpose be included on the
+      same "printed page" as the copyright notice for easier
+      identification within third-party archives.
+
+   Copyright {yyyy} {name of copyright owner}
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       https://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.

README.adoc

@@ -1,6 +1,6 @@
 image:https://spring.io/badges/spring-data-mongodb/ga.svg[Spring Data MongoDB,link=https://projects.spring.io/spring-data-mongodb#quick-start] image:https://spring.io/badges/spring-data-mongodb/snapshot.svg[Spring Data MongoDB,link=https://projects.spring.io/spring-data-mongodb#quick-start]
 
-= Spring Data MongoDB image:https://jenkins.spring.io/buildStatus/icon?job=spring-data-mongodb%2Fmaster&subject=Build[link=https://jenkins.spring.io/view/SpringData/job/spring-data-mongodb/] https://gitter.im/spring-projects/spring-data[image:https://badges.gitter.im/spring-projects/spring-data.svg[Gitter]]
+= Spring Data MongoDB image:https://jenkins.spring.io/buildStatus/icon?job=spring-data-mongodb%2Fmain&subject=Build[link=https://jenkins.spring.io/view/SpringData/job/spring-data-mongodb/] https://gitter.im/spring-projects/spring-data[image:https://badges.gitter.im/spring-projects/spring-data.svg[Gitter]]
 
 The primary goal of the https://projects.spring.io/spring-data[Spring Data] project is to make it easier to build Spring-powered applications that use new data access technologies such as non-relational databases, map-reduce frameworks, and cloud based data services.
 
@@ -8,10 +8,12 @@ The Spring Data MongoDB project aims to provide a familiar and consistent Spring
 The Spring Data MongoDB project provides integration with the MongoDB document database.
 Key functional areas of Spring Data MongoDB are a POJO centric model for interacting with a MongoDB `+Document+` and easily writing a repository style data access layer.
 
+[[code-of-conduct]]
 == Code of Conduct
 
 This project is governed by the https://github.com/spring-projects/.github/blob/e3cc2ff230d8f1dca06535aa6b5a4a23815861d4/CODE_OF_CONDUCT.md[Spring Code of Conduct]. By participating, you are expected to uphold this code of conduct. Please report unacceptable behavior to spring-code-of-conduct@pivotal.io.
 
+[[getting-started]]
 == Getting Started
 
 Here is a quick teaser of an application using Spring Data Repositories in Java:
@@ -59,6 +61,7 @@ class ApplicationConfig extends AbstractMongoClientConfiguration {
 }
 ----
 
+[[maven-configuration]]
 === Maven configuration
 
 Add the Maven dependency:
@@ -68,24 +71,25 @@ Add the Maven dependency:
 <dependency>
   <groupId>org.springframework.data</groupId>
   <artifactId>spring-data-mongodb</artifactId>
-  <version>${version}.RELEASE</version>
+  <version>${version}</version>
 </dependency>
 ----
 
-If you'd rather like the latest snapshots of the upcoming major version, use our Maven snapshot repository and declare the appropriate dependency version.
+If you'd rather like the latest snapshots of the upcoming major version, use our Maven snapshot repository
+and declare the appropriate dependency version.
 
 [source,xml]
 ----
 <dependency>
   <groupId>org.springframework.data</groupId>
   <artifactId>spring-data-mongodb</artifactId>
-  <version>${version}.BUILD-SNAPSHOT</version>
+  <version>${version}-SNAPSHOT</version>
 </dependency>
 
 <repository>
-  <id>spring-libs-snapshot</id>
+  <id>spring-snapshot</id>
   <name>Spring Snapshot Repository</name>
-  <url>https://repo.spring.io/libs-snapshot</url>
+  <url>https://repo.spring.io/snapshot</url>
 </repository>
 ----
 
@@ -98,7 +102,7 @@ Some of the changes affect the initial setup configuration as well as compile/ru
 
 .Changed XML Namespace Elements and Attributes:
 |===
-Element / Attribute | 2.x | 3.x
+| Element / Attribute | 2.x | 3.x
 
 | `<mongo:mongo-client />`
 | Used to create a `com.mongodb.MongoClient`
@@ -116,7 +120,7 @@ Use `<mongo:client-settings cluster-hosts="..." />` instead
 
 .Removed XML Namespace Elements and Attributes:
 |===
-Element / Attribute | Replacement in 3.x | Comment
+| Element / Attribute | Replacement in 3.x | Comment
 
 | `<mongo:db-factory mongo-ref="..." />`
 | `<mongo:db-factory mongo-client-ref="..." />`
@@ -133,7 +137,7 @@ Element / Attribute | Replacement in 3.x | Comment
 
 .New XML Namespace Elements and Attributes:
 |===
-Element | Comment
+| Element | Comment
 
 | `<mongo:db-factory mongo-client-ref="..." />`
 | Replacement for `<mongo:db-factory mongo-ref="..." />`
@@ -153,7 +157,7 @@ Element | Comment
 
 .Java API changes
 |===
-Type | Comment
+| Type | Comment
 
 | `MongoClientFactoryBean`
 | Creates `com.mongodb.client.MongoClient` instead of `com.mongodb.MongoClient` +
@@ -174,7 +178,7 @@ Uses `MongoClientSettings` instead of `MongoClientOptions`.
 
 .Removed Java API:
 |===
-2.x | Replacement in 3.x | Comment
+| 2.x | Replacement in 3.x | Comment
 
 | `MongoClientOptionsFactoryBean`
 | `MongoClientSettingsFactoryBean`
@@ -226,6 +230,7 @@ static class Config extends AbstractMongoClientConfiguration {
 ----
 ====
 
+[[getting-help]]
 == Getting Help
 
 Having trouble with Spring Data? We’d love to help!
@@ -239,6 +244,7 @@ If you are just starting out with Spring, try one of the https://spring.io/guide
 You can also chat with the community on https://gitter.im/spring-projects/spring-data[Gitter].
 * Report bugs with Spring Data MongoDB at https://github.com/spring-projects/spring-data-mongodb/issues[github.com/spring-projects/spring-data-mongodb/issues].
 
+[[reporting-issues]]
 == Reporting Issues
 
 Spring Data uses Github as issue tracking system to record bugs and feature requests.
@@ -249,10 +255,85 @@ If you want to raise an issue, please follow the recommendations below:
 * Please provide as much information as possible with the issue report, we like to know the version of Spring Data that you are using, the JVM version, Stacktrace, etc.
 * If you need to paste code, or include a stack trace use https://guides.github.com/features/mastering-markdown/[Markdown] code fences +++```+++.
 
+[[guides]]
+== Guides
+
+The https://spring.io/[spring.io] site contains several guides that show how to use Spring Data step-by-step:
+
+* https://spring.io/guides/gs/accessing-data-mongodb/[Accessing Data with MongoDB] is a very basic guide that shows you how to create a simple application and how to access data using repositories.
+* https://spring.io/guides/gs/accessing-mongodb-data-rest/[Accessing MongoDB Data with REST] is a guide to creating a REST web service exposing data stored in MongoDB through repositories.
+
+[[examples]]
+== Examples
+
+* https://github.com/spring-projects/spring-data-examples/[Spring Data Examples] contains example projects that explain specific features in more detail.
+
+[[building-from-source]]
 == Building from Source
 
-You don’t need to build from source to use Spring Data (binaries in https://repo.spring.io[repo.spring.io]), but if you want to try out the latest and greatest, Spring Data can be easily built with the https://github.com/takari/maven-wrapper[maven wrapper].
-You also need JDK 1.8.
+You do not need to build from source to use Spring Data. Binaries are available in https://repo.spring.io[repo.spring.io].
+and accessible from Maven using the Maven configuration noted <<maven-configuration,above>>.
+
+NOTE: Configuration for Gradle is similar to Maven.
+
+The best way to get started is by creating a Spring Boot project using MongoDB on https://start.spring.io[start.spring.io].
+Follow this https://start.spring.io/#type=maven-project&language=java&platformVersion=2.5.4&packaging=jar&jvmVersion=1.8&groupId=com.example&artifactId=demo&name=demo&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.demo&dependencies=data-mongodb[link]
+to build an imperative application and this https://start.spring.io/#type=maven-project&language=java&platformVersion=2.5.4&packaging=jar&jvmVersion=1.8&groupId=com.example&artifactId=demo&name=demo&description=Demo%20project%20for%20Spring%20Boot&packageName=com.example.demo&dependencies=data-mongodb-reactive[link]
+to build a reactive one.
+
+However, if you want to try out the latest and greatest, Spring Data can be easily built with the https://github.com/takari/maven-wrapper[maven wrapper]
+and minimally JDK 8 (https://www.oracle.com/java/technologies/downloads/[JDK downloads]).
+
+In order to build Spring Data MongoDB, first you will need to https://www.mongodb.com/try/download/community[download]
+and https://docs.mongodb.com/manual/installation/[install a MongoDB distribution].
+
+Once you have installed MongoDB, you need to start a MongoDB server. It is convenient to set an environment variable to
+your MongoDB installation (e.g. `MONGODB_HOME`).
+
+To run the full test suite a https://docs.mongodb.com/manual/tutorial/deploy-replica-set/[MongoDB Replica Set] is required.
+
+To run the MongoDB server enter the following command from a command-line:
+
+[source,bash]
+----
+$ $MONGODB_HOME/bin/mongod --dbpath $MONGODB_HOME/runtime/data --ipv6 --port 27017 --replSet rs0
+...
+"msg":"Successfully connected to host"
+----
+
+Once the MongoDB server starts up, you should see the message (`msg`), "_Successfully connected to host_".
+
+Notice the `--dbpath` option to the `mongod` command. You can set this to anything you like, but in this case, we set
+the absolute path to a sub-directory (`runtime/data/`) under the MongoDB installation directory (in `$MONGODB_HOME`).
+
+You need to initialize the MongoDB replica set only once on the first time the MongoDB server is started.
+To initialize the replica set, start a mongo client:
+
+[source,bash]
+----
+$ $MONGODB_HOME/bin/mongo
+MongoDB server version: 5.0.0
+...
+----
+
+Then enter the following command:
+
+[source,bash]
+----
+mongo> rs.initiate({ _id: 'rs0', members: [ { _id: 0, host: '127.0.0.1:27017' } ] })
+----
+
+Finally, on UNIX-based system (for example, Linux or Mac OS X) you may need to adjust the `ulimit`.
+In case you need to, you can adjust the `ulimit` with the following command (32768 is just a recommendation):
+
+[source,bash]
+----
+$ ulimit -n 32768
+----
+
+You can use `ulimit -a` again to verify the `ulimit` on "_open files_" was set appropriately.
+
+Now you are ready to build Spring Data MongoDB. Simply enter the following `mvnw` (Maven Wrapper) command:
 
 [source,bash]
 ----
@@ -261,7 +342,8 @@ You also need JDK 1.8.
 
 If you want to build with the regular `mvn` command, you will need https://maven.apache.org/run-maven/index.html[Maven v3.5.0 or above].
 
-_Also see link:CONTRIBUTING.adoc[CONTRIBUTING.adoc] if you wish to submit pull requests, and in particular please sign the https://cla.pivotal.io/sign/spring[Contributor’s Agreement] before your first non-trivial change._
+_Also see link:CONTRIBUTING.adoc[CONTRIBUTING.adoc] if you wish to submit pull requests, and in particular, please sign
+the https://cla.pivotal.io/sign/spring[Contributor’s Agreement] before your first non-trivial change._
 
 === Building reference documentation
 
@@ -274,17 +356,7 @@ Building the documentation builds also the project without running tests.
 
 The generated documentation is available from `target/site/reference/html/index.html`.
 
-== Guides
-
-The https://spring.io/[spring.io] site contains several guides that show how to use Spring Data step-by-step:
-
-* https://spring.io/guides/gs/accessing-data-mongodb/[Accessing Data with MongoDB] is a very basic guide that shows you how to create a simple application and how to access data using repositories.
-* https://spring.io/guides/gs/accessing-mongodb-data-rest/[Accessing MongoDB Data with REST] is a guide to creating a REST web service exposing data stored in MongoDB through repositories.
-
-== Examples
-
-* https://github.com/spring-projects/spring-data-examples/[Spring Data Examples] contains example projects that explain specific features in more detail.
-
+[[license]]
 == License
 
 Spring Data MongoDB is Open Source software released under the https://www.apache.org/licenses/LICENSE-2.0.html[Apache 2.0 license].

ci/openjdk11-mongodb-4.2/Dockerfile

@@ -1,15 +0,0 @@
-FROM adoptopenjdk/openjdk11:latest
-
-ENV TZ=Etc/UTC
-ENV DEBIAN_FRONTEND=noninteractive
-
-RUN set -eux; \
-	apt-get update && apt-get install -y apt-transport-https apt-utils gnupg2 ; \
-	apt-key adv --keyserver hkps://keyserver.ubuntu.com:443 --recv e162f504a20cdf15827f718d4b7c549a058f8b6b ; \
-	echo "deb [ arch=amd64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.2 multiverse" | tee /etc/apt/sources.list.d/mongodb-org-4.2.list; \
-	echo ${TZ} > /etc/timezone;
-
-RUN apt-get update ; \
-	apt-get install -y mongodb-org=4.2.0 mongodb-org-server=4.2.0 mongodb-org-shell=4.2.0 mongodb-org-mongos=4.2.0 mongodb-org-tools=4.2.0 ; \
-	apt-get clean; \
-	rm -rf /var/lib/apt/lists/*;

ci/openjdk11-mongodb-4.4/Dockerfile

@@ -0,0 +1,18 @@
+FROM adoptopenjdk/openjdk11:latest
+
+ENV TZ=Etc/UTC
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN set -eux; \
+	sed -i -e 's/archive.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/security.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/http/https/g' /etc/apt/sources.list ; \
+	apt-get update && apt-get install -y apt-transport-https apt-utils gnupg2 ; \
+	apt-key adv --keyserver hkps://keyserver.ubuntu.com:443 --recv 656408E390CFB1F5 ; \
+	echo "deb [ arch=amd64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.4 multiverse" | tee /etc/apt/sources.list.d/mongodb-org-4.4.list; \
+	echo ${TZ} > /etc/timezone;
+
+RUN apt-get update ; \
+	apt-get install -y mongodb-org=4.4.4 mongodb-org-server=4.4.4 mongodb-org-shell=4.4.4 mongodb-org-mongos=4.4.4 mongodb-org-tools=4.4.4 ; \
+	apt-get clean; \
+	rm -rf /var/lib/apt/lists/*;

ci/openjdk15-mongodb-4.2/Dockerfile

@@ -1,15 +0,0 @@
-FROM adoptopenjdk/openjdk15:latest
-
-ENV TZ=Etc/UTC
-ENV DEBIAN_FRONTEND=noninteractive
-
-RUN set -eux; \
-	apt-get update && apt-get install -y apt-transport-https apt-utils gnupg2 ; \
-	apt-key adv --keyserver hkps://keyserver.ubuntu.com:443 --recv e162f504a20cdf15827f718d4b7c549a058f8b6b ; \
-	echo "deb [ arch=amd64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.2 multiverse" | tee /etc/apt/sources.list.d/mongodb-org-4.2.list; \
-	echo ${TZ} > /etc/timezone;
-
-RUN apt-get update ; \
-	apt-get install -y mongodb-org=4.2.0 mongodb-org-server=4.2.0 mongodb-org-shell=4.2.0 mongodb-org-mongos=4.2.0 mongodb-org-tools=4.2.0 ; \
-	apt-get clean; \
-	rm -rf /var/lib/apt/lists/*;

ci/openjdk16-mongodb-4.4/Dockerfile

@@ -0,0 +1,18 @@
+FROM adoptopenjdk/openjdk16:latest
+
+ENV TZ=Etc/UTC
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN set -eux; \
+	sed -i -e 's/archive.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/security.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/http/https/g' /etc/apt/sources.list ; \
+	apt-get update && apt-get install -y apt-transport-https apt-utils gnupg2 ; \
+	apt-key adv --keyserver hkps://keyserver.ubuntu.com:443 --recv 656408E390CFB1F5 ; \
+	echo "deb [ arch=amd64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.4 multiverse" | tee /etc/apt/sources.list.d/mongodb-org-4.4.list; \
+	echo ${TZ} > /etc/timezone;
+
+RUN apt-get update ; \
+	apt-get install -y mongodb-org=4.4.4 mongodb-org-server=4.4.4 mongodb-org-shell=4.4.4 mongodb-org-mongos=4.4.4 mongodb-org-tools=4.4.4 ; \
+	apt-get clean; \
+	rm -rf /var/lib/apt/lists/*;

ci/openjdk8-mongodb-4.0/Dockerfile

@@ -4,12 +4,15 @@ ENV TZ=Etc/UTC
 ENV DEBIAN_FRONTEND=noninteractive
 
 RUN RUN set -eux; \
+	sed -i -e 's/archive.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/security.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/http/https/g' /etc/apt/sources.list ; \
 	apt-get update && apt-get install -y apt-transport-https apt-utils gnupg2 ; \
 	apt-key adv --keyserver hkps://keyserver.ubuntu.com:443 --recv 9DA31620334BD75D9DCB49F368818C72E52529D4 ; \
 	echo "deb [ arch=amd64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.0 multiverse" | tee /etc/apt/sources.list.d/mongodb-org-4.0.list; \
 	echo ${TZ} > /etc/timezone;
 
 RUN apt-get update ; \
-	apt-get install -y mongodb-org=4.0.14 mongodb-org-server=4.0.14 mongodb-org-shell=4.0.14 mongodb-org-mongos=4.0.14 mongodb-org-tools=4.0.14 ; \
+	apt-get install -y mongodb-org=4.0.23 mongodb-org-server=4.0.23 mongodb-org-shell=4.0.23 mongodb-org-mongos=4.0.23 mongodb-org-tools=4.0.23 ; \
 	apt-get clean; \
 	rm -rf /var/lib/apt/lists/*;

ci/openjdk8-mongodb-4.2/Dockerfile

@@ -1,15 +0,0 @@
-FROM adoptopenjdk/openjdk8:latest
-
-ENV TZ=Etc/UTC
-ENV DEBIAN_FRONTEND=noninteractive
-
-RUN set -eux; \
-	apt-get update && apt-get install -y apt-transport-https apt-utils gnupg2 ; \
-	apt-key adv --keyserver hkps://keyserver.ubuntu.com:443 --recv e162f504a20cdf15827f718d4b7c549a058f8b6b ; \
-	echo "deb [ arch=amd64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.2 multiverse" | tee /etc/apt/sources.list.d/mongodb-org-4.2.list; \
-	echo ${TZ} > /etc/timezone;
-
-RUN apt-get update ; \
-	apt-get install -y mongodb-org=4.2.0 mongodb-org-server=4.2.0 mongodb-org-shell=4.2.0 mongodb-org-mongos=4.2.0 mongodb-org-tools=4.2.0 ; \
-	apt-get clean; \
-	rm -rf /var/lib/apt/lists/*;

ci/openjdk8-mongodb-4.4/Dockerfile

@@ -0,0 +1,20 @@
+FROM adoptopenjdk/openjdk8:latest
+
+ENV TZ=Etc/UTC
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN set -eux; \
+	sed -i -e 's/archive.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/security.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/http/https/g' /etc/apt/sources.list ; \
+	apt-get update && apt-get install -y apt-transport-https apt-utils gnupg2 ; \
+	apt-key adv --keyserver hkps://keyserver.ubuntu.com:443 --recv 656408E390CFB1F5 ; \
+	echo "deb [ arch=amd64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.4 multiverse" | tee /etc/apt/sources.list.d/mongodb-org-4.4.list; \
+	echo ${TZ} > /etc/timezone;
+
+RUN apt-get update ; \
+	ln -T /bin/true /usr/bin/systemctl ; \
+	apt-get install -y mongodb-org=4.4.4 mongodb-org-server=4.4.4 mongodb-org-shell=4.4.4 mongodb-org-mongos=4.4.4 mongodb-org-tools=4.4.4 ; \
+	rm /usr/bin/systemctl ; \
+	apt-get clean; \
+	rm -rf /var/lib/apt/lists/*;

ci/openjdk8-mongodb-5.0/Dockerfile

@@ -0,0 +1,20 @@
+FROM adoptopenjdk/openjdk8:latest
+
+ENV TZ=Etc/UTC
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN set -eux; \
+	sed -i -e 's/archive.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/security.ubuntu.com/mirror.one.com/g' /etc/apt/sources.list; \
+	sed -i -e 's/http/https/g' /etc/apt/sources.list ; \
+	apt-get update && apt-get install -y apt-transport-https apt-utils gnupg2 wget ; \
+	# MongoDB 5.0 release signing key
+	apt-key adv --keyserver hkps://keyserver.ubuntu.com:443 --recv B00A0BD1E2C63C11 ; \
+	# Needed when MongoDB creates a 5.0 folder.
+	echo "deb [ arch=amd64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/5.0 multiverse" | tee /etc/apt/sources.list.d/mongodb-org-5.0.list; \
+	echo ${TZ} > /etc/timezone;
+
+RUN apt-get update; \
+	apt-get install -y mongodb-org=5.0.3 mongodb-org-server=5.0.3 mongodb-org-shell=5.0.3 mongodb-org-mongos=5.0.3 mongodb-org-tools=5.0.3; \
+	apt-get clean; \
+	rm -rf /var/lib/apt/lists/*;

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-mongodb-parent</artifactId>
-	<version>3.2.0-M2</version>
+	<version>3.3.0-RC1</version>
 	<packaging>pom</packaging>
 
 	<name>Spring Data MongoDB</name>
@@ -15,7 +15,7 @@
 	<parent>
 		<groupId>org.springframework.data.build</groupId>
 		<artifactId>spring-data-parent</artifactId>
-		<version>2.5.0-M2</version>
+		<version>2.6.0-RC1</version>
 	</parent>
 
 	<modules>
@@ -26,8 +26,8 @@
 	<properties>
 		<project.type>multi</project.type>
 		<dist.id>spring-data-mongodb</dist.id>
-		<springdata.commons>2.5.0-M2</springdata.commons>
-		<mongo>4.1.1</mongo>
+		<springdata.commons>2.6.0-RC1</springdata.commons>
+		<mongo>4.4.0-beta1</mongo>
 		<mongo.reactivestreams>${mongo}</mongo.reactivestreams>
 		<jmh.version>1.19</jmh.version>
 	</properties>
@@ -141,11 +141,11 @@
 			<id>sonatype-libs-snapshot</id>
 			<url>https://oss.sonatype.org/content/repositories/snapshots</url>
 			<releases>
-        <enabled>false</enabled>
-      </releases>
+				<enabled>false</enabled>
+			</releases>
 			<snapshots>
-        <enabled>true</enabled>
-      </snapshots>
+				<enabled>true</enabled>
+			</snapshots>
 		</repository>
 	</repositories>
 
@@ -158,11 +158,6 @@
 			<id>spring-libs-milestone</id>
 			<url>https://repo.spring.io/libs-milestone</url>
 		</pluginRepository>
-		<pluginRepository>
-			<id>bintray-plugins</id>
-			<name>bintray-plugins</name>
-			<url>https://jcenter.bintray.com</url>
-		</pluginRepository>
 	</pluginRepositories>
 
 </project>

settings.xml

@@ -0,0 +1,29 @@
+<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
+          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
+                      https://maven.apache.org/xsd/settings-1.0.0.xsd">
+
+	<servers>
+		<server>
+			<id>spring-plugins-release</id>
+			<username>${env.ARTIFACTORY_USR}</username>
+			<password>${env.ARTIFACTORY_PSW}</password>
+		</server>
+		<server>
+			<id>spring-libs-snapshot</id>
+			<username>${env.ARTIFACTORY_USR}</username>
+			<password>${env.ARTIFACTORY_PSW}</password>
+		</server>
+		<server>
+			<id>spring-libs-milestone</id>
+			<username>${env.ARTIFACTORY_USR}</username>
+			<password>${env.ARTIFACTORY_PSW}</password>
+		</server>
+		<server>
+			<id>spring-libs-release</id>
+			<username>${env.ARTIFACTORY_USR}</username>
+			<password>${env.ARTIFACTORY_PSW}</password>
+		</server>
+	</servers>
+
+</settings>

spring-data-mongodb-benchmarks/pom.xml

@@ -7,7 +7,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.2.0-M2</version>
+		<version>3.3.0-RC1</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb-distribution/pom.xml

@@ -14,7 +14,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.2.0-M2</version>
+		<version>3.3.0-RC1</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

spring-data-mongodb/pom.xml

@@ -11,7 +11,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.2.0-M2</version>
+		<version>3.3.0-RC1</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 
@@ -87,6 +87,13 @@
 			<optional>true</optional>
 		</dependency>
 
+		<dependency>
+			<groupId>com.google.code.findbugs</groupId>
+			<artifactId>jsr305</artifactId>
+			<version>3.0.2</version>
+			<optional>true</optional>
+		</dependency>
+
 		<!-- reactive -->
 
 		<dependency>
@@ -310,6 +317,15 @@
 			<scope>test</scope>
 		</dependency>
 
+		<!-- jMolecules -->
+
+		<dependency>
+			<groupId>org.jmolecules</groupId>
+			<artifactId>jmolecules-ddd</artifactId>
+			<version>${jmolecules}</version>
+			<scope>test</scope>
+		</dependency>
+
 	</dependencies>
 
 	<build>

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/BindableMongoExpression.java

@@ -0,0 +1,152 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb;
+
+import java.util.Arrays;
+
+import org.bson.Document;
+import org.bson.codecs.DocumentCodec;
+import org.bson.codecs.configuration.CodecRegistry;
+import org.springframework.data.mongodb.util.json.ParameterBindingDocumentCodec;
+import org.springframework.data.util.Lazy;
+import org.springframework.lang.Nullable;
+import org.springframework.util.ObjectUtils;
+import org.springframework.util.StringUtils;
+
+/**
+ * A {@link MongoExpression} using the {@link ParameterBindingDocumentCodec} for parsing a raw ({@literal json})
+ * expression. The expression will be wrapped within <code>{ ... }</code> if necessary. The actual parsing and parameter
+ * binding of placeholders like {@code ?0} is delayed upon first call on the the target {@link Document} via
+ * {@link #toDocument()}.
+ * <br />
+ *
+ * <pre class="code">
+ * $toUpper : $name                -> { '$toUpper' : '$name' }
+ *
+ * { '$toUpper' : '$name' }        -> { '$toUpper' : '$name' }
+ *
+ * { '$toUpper' : '?0' }, "$name"  -> { '$toUpper' : '$name' }
+ * </pre>
+ *
+ * Some types might require a special {@link org.bson.codecs.Codec}. If so, make sure to provide a {@link CodecRegistry}
+ * containing the required {@link org.bson.codecs.Codec codec} via {@link #withCodecRegistry(CodecRegistry)}.
+ *
+ * @author Christoph Strobl
+ * @since 3.2
+ */
+public class BindableMongoExpression implements MongoExpression {
+
+	private final String expressionString;
+
+	private final @Nullable CodecRegistryProvider codecRegistryProvider;
+
+	private final @Nullable Object[] args;
+
+	private final Lazy<Document> target;
+
+	/**
+	 * Create a new instance of {@link BindableMongoExpression}.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @param args can be {@literal null}.
+	 */
+	public BindableMongoExpression(String expression, @Nullable Object[] args) {
+		this(expression, null, args);
+	}
+
+	/**
+	 * Create a new instance of {@link BindableMongoExpression}.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @param codecRegistryProvider can be {@literal null}.
+	 * @param args can be {@literal null}.
+	 */
+	public BindableMongoExpression(String expression, @Nullable CodecRegistryProvider codecRegistryProvider,
+			@Nullable Object[] args) {
+
+		this.expressionString = expression;
+		this.codecRegistryProvider = codecRegistryProvider;
+		this.args = args;
+		this.target = Lazy.of(this::parse);
+	}
+
+	/**
+	 * Provide the {@link CodecRegistry} used to convert expressions.
+	 *
+	 * @param codecRegistry must not be {@literal null}.
+	 * @return new instance of {@link BindableMongoExpression}.
+	 */
+	public BindableMongoExpression withCodecRegistry(CodecRegistry codecRegistry) {
+		return new BindableMongoExpression(expressionString, () -> codecRegistry, args);
+	}
+
+	/**
+	 * Provide the arguments to bind to the placeholders via their index.
+	 *
+	 * @param args must not be {@literal null}.
+	 * @return new instance of {@link BindableMongoExpression}.
+	 */
+	public BindableMongoExpression bind(Object... args) {
+		return new BindableMongoExpression(expressionString, codecRegistryProvider, args);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.MongoExpression#toDocument()
+	 */
+	@Override
+	public Document toDocument() {
+		return target.get();
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see java.lang.Object#toString()
+	 */
+	@Override
+	public String toString() {
+		return "BindableMongoExpression{" + "expressionString='" + expressionString + '\'' + ", args="
+				+ Arrays.toString(args) + '}';
+	}
+
+	private Document parse() {
+
+		String expression = wrapJsonIfNecessary(expressionString);
+
+		if (ObjectUtils.isEmpty(args)) {
+
+			if (codecRegistryProvider == null) {
+				return Document.parse(expression);
+			}
+
+			return Document.parse(expression, codecRegistryProvider.getCodecFor(Document.class)
+					.orElseGet(() -> new DocumentCodec(codecRegistryProvider.getCodecRegistry())));
+		}
+
+		ParameterBindingDocumentCodec codec = codecRegistryProvider == null ? new ParameterBindingDocumentCodec()
+				: new ParameterBindingDocumentCodec(codecRegistryProvider.getCodecRegistry());
+		return codec.decode(expression, args);
+	}
+
+	private static String wrapJsonIfNecessary(String json) {
+
+		if (StringUtils.hasText(json) && (json.startsWith("{") && json.endsWith("}"))) {
+			return json;
+		}
+
+		return "{" + json + "}";
+	}
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/MongoCollectionUtils.java

@@ -20,8 +20,8 @@ import org.springframework.util.StringUtils;
 
 /**
  * Helper class featuring helper methods for working with MongoDb collections.
- * <p/>
- * <p/>
+ * <br />
+ * <br />
  * Mainly intended for internal use within the framework.
  *
  * @author Thomas Risberg

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/MongoDatabaseUtils.java

@@ -30,7 +30,7 @@ import com.mongodb.client.MongoDatabase;
  * Helper class for managing a {@link MongoDatabase} instances via {@link MongoDatabaseFactory}. Used for obtaining
  * {@link ClientSession session bound} resources, such as {@link MongoDatabase} and
  * {@link com.mongodb.client.MongoCollection} suitable for transactional usage.
- * <p />
+ * <br />
  * <strong>Note:</strong> Intended for internal usage only.
  *
  * @author Christoph Strobl
@@ -43,7 +43,7 @@ public class MongoDatabaseUtils {
 	/**
 	 * Obtain the default {@link MongoDatabase database} form the given {@link MongoDatabaseFactory factory} using
 	 * {@link SessionSynchronization#ON_ACTUAL_TRANSACTION native session synchronization}.
-	 * <p />
+	 * <br />
 	 * Registers a {@link MongoSessionSynchronization MongoDB specific transaction synchronization} within the current
 	 * {@link Thread} if {@link TransactionSynchronizationManager#isSynchronizationActive() synchronization is active}.
 	 *
@@ -56,7 +56,7 @@ public class MongoDatabaseUtils {
 
 	/**
 	 * Obtain the default {@link MongoDatabase database} form the given {@link MongoDatabaseFactory factory}.
-	 * <p />
+	 * <br />
 	 * Registers a {@link MongoSessionSynchronization MongoDB specific transaction synchronization} within the current
 	 * {@link Thread} if {@link TransactionSynchronizationManager#isSynchronizationActive() synchronization is active}.
 	 *
@@ -71,7 +71,7 @@ public class MongoDatabaseUtils {
 	/**
 	 * Obtain the {@link MongoDatabase database} with given name form the given {@link MongoDatabaseFactory factory} using
 	 * {@link SessionSynchronization#ON_ACTUAL_TRANSACTION native session synchronization}.
-	 * <p />
+	 * <br />
 	 * Registers a {@link MongoSessionSynchronization MongoDB specific transaction synchronization} within the current
 	 * {@link Thread} if {@link TransactionSynchronizationManager#isSynchronizationActive() synchronization is active}.
 	 *
@@ -85,7 +85,7 @@ public class MongoDatabaseUtils {
 
 	/**
 	 * Obtain the {@link MongoDatabase database} with given name form the given {@link MongoDatabaseFactory factory}.
-	 * <p />
+	 * <br />
 	 * Registers a {@link MongoSessionSynchronization MongoDB specific transaction synchronization} within the current
 	 * {@link Thread} if {@link TransactionSynchronizationManager#isSynchronizationActive() synchronization is active}.
 	 *
@@ -104,7 +104,8 @@ public class MongoDatabaseUtils {
 
 		Assert.notNull(factory, "Factory must not be null!");
 
-		if (!TransactionSynchronizationManager.isSynchronizationActive()) {
+		if (sessionSynchronization == SessionSynchronization.NEVER
+				|| !TransactionSynchronizationManager.isSynchronizationActive()) {
 			return StringUtils.hasText(dbName) ? factory.getMongoDatabase(dbName) : factory.getMongoDatabase();
 		}
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/MongoExpression.java

@@ -0,0 +1,73 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb;
+
+/**
+ * Wrapper object for MongoDB expressions like {@code $toUpper : $name} that manifest as {@link org.bson.Document} when
+ * passed on to the driver.
+ * <br />
+ * A set of predefined {@link MongoExpression expressions}, including a
+ * {@link org.springframework.data.mongodb.core.aggregation.AggregationSpELExpression SpEL based variant} for method
+ * like expressions (eg. {@code toUpper(name)}) are available via the
+ * {@link org.springframework.data.mongodb.core.aggregation Aggregation API}.
+ *
+ * @author Christoph Strobl
+ * @since 3.2
+ * @see org.springframework.data.mongodb.core.aggregation.ArithmeticOperators
+ * @see org.springframework.data.mongodb.core.aggregation.ArrayOperators
+ * @see org.springframework.data.mongodb.core.aggregation.ComparisonOperators
+ * @see org.springframework.data.mongodb.core.aggregation.ConditionalOperators
+ * @see org.springframework.data.mongodb.core.aggregation.ConvertOperators
+ * @see org.springframework.data.mongodb.core.aggregation.DateOperators
+ * @see org.springframework.data.mongodb.core.aggregation.ObjectOperators
+ * @see org.springframework.data.mongodb.core.aggregation.SetOperators
+ * @see org.springframework.data.mongodb.core.aggregation.StringOperators
+ */
+@FunctionalInterface
+public interface MongoExpression {
+
+	/**
+	 * Create a new {@link MongoExpression} from plain {@link String} (eg. {@code $toUpper : $name}). <br />
+	 * The given expression will be wrapped with <code>{ ... }</code> to match an actual MongoDB {@link org.bson.Document}
+	 * if necessary.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @return new instance of {@link MongoExpression}.
+	 */
+	static MongoExpression create(String expression) {
+		return new BindableMongoExpression(expression, null);
+	}
+
+	/**
+	 * Create a new {@link MongoExpression} from plain {@link String} containing placeholders (eg. {@code $toUpper : ?0})
+	 * that will be resolved on first call of {@link #toDocument()}. <br />
+	 * The given expression will be wrapped with <code>{ ... }</code> to match an actual MongoDB {@link org.bson.Document}
+	 * if necessary.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @return new instance of {@link MongoExpression}.
+	 */
+	static MongoExpression create(String expression, Object... args) {
+		return new BindableMongoExpression(expression, args);
+	}
+
+	/**
+	 * Obtain the native {@link org.bson.Document} representation.
+	 *
+	 * @return never {@literal null}.
+	 */
+	org.bson.Document toDocument();
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/MongoResourceHolder.java

@@ -24,7 +24,7 @@ import com.mongodb.client.ClientSession;
 /**
  * MongoDB specific {@link ResourceHolderSupport resource holder}, wrapping a {@link ClientSession}.
  * {@link MongoTransactionManager} binds instances of this class to the thread.
- * <p />
+ * <br />
  * <strong>Note:</strong> Intended for internal usage only.
  *
  * @author Christoph Strobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/MongoTransactionManager.java

@@ -37,18 +37,18 @@ import com.mongodb.client.ClientSession;
 /**
  * A {@link org.springframework.transaction.PlatformTransactionManager} implementation that manages
  * {@link ClientSession} based transactions for a single {@link MongoDatabaseFactory}.
- * <p />
+ * <br />
  * Binds a {@link ClientSession} from the specified {@link MongoDatabaseFactory} to the thread.
- * <p />
+ * <br />
  * {@link TransactionDefinition#isReadOnly() Readonly} transactions operate on a {@link ClientSession} and enable causal
  * consistency, and also {@link ClientSession#startTransaction() start}, {@link ClientSession#commitTransaction()
  * commit} or {@link ClientSession#abortTransaction() abort} a transaction.
- * <p />
+ * <br />
  * Application code is required to retrieve the {@link com.mongodb.client.MongoDatabase} via
  * {@link MongoDatabaseUtils#getDatabase(MongoDatabaseFactory)} instead of a standard
  * {@link MongoDatabaseFactory#getMongoDatabase()} call. Spring classes such as
  * {@link org.springframework.data.mongodb.core.MongoTemplate} use this strategy implicitly.
- * <p />
+ * <br />
  * By default failure of a {@literal commit} operation raises a {@link TransactionSystemException}. One may override
  * {@link #doCommit(MongoTransactionObject)} to implement the
  * <a href="https://docs.mongodb.com/manual/core/transactions/#retry-commit-operation">Retry Commit Operation</a>
@@ -69,11 +69,11 @@ public class MongoTransactionManager extends AbstractPlatformTransactionManager
 
 	/**
 	 * Create a new {@link MongoTransactionManager} for bean-style usage.
-	 * <p />
+	 * <br />
 	 * <strong>Note:</strong>The {@link MongoDatabaseFactory db factory} has to be
 	 * {@link #setDbFactory(MongoDatabaseFactory) set} before using the instance. Use this constructor to prepare a
 	 * {@link MongoTransactionManager} via a {@link org.springframework.beans.factory.BeanFactory}.
-	 * <p />
+	 * <br />
 	 * Optionally it is possible to set default {@link TransactionOptions transaction options} defining
 	 * {@link com.mongodb.ReadConcern} and {@link com.mongodb.WriteConcern}.
 	 *
@@ -212,8 +212,8 @@ public class MongoTransactionManager extends AbstractPlatformTransactionManager
 	 * By default those labels are ignored, nevertheless one might check for
 	 * {@link MongoException#UNKNOWN_TRANSACTION_COMMIT_RESULT_LABEL transient commit errors labels} and retry the the
 	 * commit. <br />
+	 * <pre>
 	 * <code>
-	 *     <pre>
 	 * int retries = 3;
 	 * do {
 	 *     try {
@@ -226,8 +226,8 @@ public class MongoTransactionManager extends AbstractPlatformTransactionManager
 	 *     }
 	 *     Thread.sleep(500);
 	 * } while (--retries > 0);
-	 *     </pre>
 	 * </code>
+	 * </pre>
 	 *
 	 * @param transactionObject never {@literal null}.
 	 * @throws Exception in case of transaction errors.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/ReactiveMongoDatabaseUtils.java

@@ -36,7 +36,7 @@ import com.mongodb.reactivestreams.client.MongoDatabase;
  * Helper class for managing reactive {@link MongoDatabase} instances via {@link ReactiveMongoDatabaseFactory}. Used for
  * obtaining {@link ClientSession session bound} resources, such as {@link MongoDatabase} and {@link MongoCollection}
  * suitable for transactional usage.
- * <p />
+ * <br />
  * <strong>Note:</strong> Intended for internal usage only.
  *
  * @author Mark Paluch
@@ -75,7 +75,7 @@ public class ReactiveMongoDatabaseUtils {
 	/**
 	 * Obtain the default {@link MongoDatabase database} form the given {@link ReactiveMongoDatabaseFactory factory} using
 	 * {@link SessionSynchronization#ON_ACTUAL_TRANSACTION native session synchronization}.
-	 * <p />
+	 * <br />
 	 * Registers a {@link MongoSessionSynchronization MongoDB specific transaction synchronization} within the subscriber
 	 * {@link Context} if {@link TransactionSynchronizationManager#isSynchronizationActive() synchronization is active}.
 	 *
@@ -88,7 +88,7 @@ public class ReactiveMongoDatabaseUtils {
 
 	/**
 	 * Obtain the default {@link MongoDatabase database} form the given {@link ReactiveMongoDatabaseFactory factory}.
-	 * <p />
+	 * <br />
 	 * Registers a {@link MongoSessionSynchronization MongoDB specific transaction synchronization} within the subscriber
 	 * {@link Context} if {@link TransactionSynchronizationManager#isSynchronizationActive() synchronization is active}.
 	 *
@@ -104,7 +104,7 @@ public class ReactiveMongoDatabaseUtils {
 	/**
 	 * Obtain the {@link MongoDatabase database} with given name form the given {@link ReactiveMongoDatabaseFactory
 	 * factory} using {@link SessionSynchronization#ON_ACTUAL_TRANSACTION native session synchronization}.
-	 * <p />
+	 * <br />
 	 * Registers a {@link MongoSessionSynchronization MongoDB specific transaction synchronization} within the subscriber
 	 * {@link Context} if {@link TransactionSynchronizationManager#isSynchronizationActive() synchronization is active}.
 	 *
@@ -119,7 +119,7 @@ public class ReactiveMongoDatabaseUtils {
 	/**
 	 * Obtain the {@link MongoDatabase database} with given name form the given {@link ReactiveMongoDatabaseFactory
 	 * factory}.
-	 * <p />
+	 * <br />
 	 * Registers a {@link MongoSessionSynchronization MongoDB specific transaction synchronization} within the subscriber
 	 * {@link Context} if {@link TransactionSynchronizationManager#isSynchronizationActive() synchronization is active}.
 	 *
@@ -138,6 +138,10 @@ public class ReactiveMongoDatabaseUtils {
 
 		Assert.notNull(factory, "DatabaseFactory must not be null!");
 
+		if (sessionSynchronization == SessionSynchronization.NEVER) {
+			return getMongoDatabaseOrDefault(dbName, factory);
+		}
+
 		return TransactionSynchronizationManager.forCurrentTransaction()
 				.filter(TransactionSynchronizationManager::isSynchronizationActive) //
 				.flatMap(synchronizationManager -> {

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/ReactiveMongoResourceHolder.java

@@ -24,7 +24,7 @@ import com.mongodb.reactivestreams.client.ClientSession;
 /**
  * MongoDB specific resource holder, wrapping a {@link ClientSession}. {@link ReactiveMongoTransactionManager} binds
  * instances of this class to the subscriber context.
- * <p />
+ * <br />
  * <strong>Note:</strong> Intended for internal usage only.
  *
  * @author Mark Paluch

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/ReactiveMongoTransactionManager.java

@@ -38,21 +38,21 @@ import com.mongodb.reactivestreams.client.ClientSession;
  * A {@link org.springframework.transaction.ReactiveTransactionManager} implementation that manages
  * {@link com.mongodb.reactivestreams.client.ClientSession} based transactions for a single
  * {@link org.springframework.data.mongodb.ReactiveMongoDatabaseFactory}.
- * <p />
+ * <br />
  * Binds a {@link ClientSession} from the specified
  * {@link org.springframework.data.mongodb.ReactiveMongoDatabaseFactory} to the subscriber
  * {@link reactor.util.context.Context}.
- * <p />
+ * <br />
  * {@link org.springframework.transaction.TransactionDefinition#isReadOnly() Readonly} transactions operate on a
  * {@link ClientSession} and enable causal consistency, and also {@link ClientSession#startTransaction() start},
  * {@link com.mongodb.reactivestreams.client.ClientSession#commitTransaction() commit} or
  * {@link ClientSession#abortTransaction() abort} a transaction.
- * <p />
+ * <br />
  * Application code is required to retrieve the {@link com.mongodb.reactivestreams.client.MongoDatabase} via
  * {@link org.springframework.data.mongodb.ReactiveMongoDatabaseUtils#getDatabase(ReactiveMongoDatabaseFactory)} instead
  * of a standard {@link org.springframework.data.mongodb.ReactiveMongoDatabaseFactory#getMongoDatabase()} call. Spring
  * classes such as {@link org.springframework.data.mongodb.core.ReactiveMongoTemplate} use this strategy implicitly.
- * <p />
+ * <br />
  * By default failure of a {@literal commit} operation raises a {@link TransactionSystemException}. You can override
  * {@link #doCommit(TransactionSynchronizationManager, ReactiveMongoTransactionObject)} to implement the
  * <a href="https://docs.mongodb.com/manual/core/transactions/#retry-commit-operation">Retry Commit Operation</a>
@@ -71,11 +71,11 @@ public class ReactiveMongoTransactionManager extends AbstractReactiveTransaction
 
 	/**
 	 * Create a new {@link ReactiveMongoTransactionManager} for bean-style usage.
-	 * <p />
+	 * <br />
 	 * <strong>Note:</strong>The {@link org.springframework.data.mongodb.ReactiveMongoDatabaseFactory db factory} has to
 	 * be {@link #setDatabaseFactory(ReactiveMongoDatabaseFactory)} set} before using the instance. Use this constructor
 	 * to prepare a {@link ReactiveMongoTransactionManager} via a {@link org.springframework.beans.factory.BeanFactory}.
-	 * <p />
+	 * <br />
 	 * Optionally it is possible to set default {@link TransactionOptions transaction options} defining
 	 * {@link com.mongodb.ReadConcern} and {@link com.mongodb.WriteConcern}.
 	 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/SessionAwareMethodInterceptor.java

@@ -35,7 +35,7 @@ import com.mongodb.session.ClientSession;
 /**
  * {@link MethodInterceptor} implementation looking up and invoking an alternative target method having
  * {@link ClientSession} as its first argument. This allows seamless integration with the existing code base.
- * <p />
+ * <br />
  * The {@link MethodInterceptor} is aware of methods on {@code MongoCollection} that my return new instances of itself
  * like (eg. {@link com.mongodb.reactivestreams.client.MongoCollection#withWriteConcern(WriteConcern)} and decorate them
  * if not already proxied.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/SessionSynchronization.java

@@ -15,13 +15,20 @@
  */
 package org.springframework.data.mongodb;
 
+import org.springframework.data.mongodb.core.MongoTemplate;
+import org.springframework.data.mongodb.core.ReactiveMongoTemplate;
+
 /**
- * {@link SessionSynchronization} is used along with {@link org.springframework.data.mongodb.core.MongoTemplate} to
- * define in which type of transactions to participate if any.
+ * {@link SessionSynchronization} is used along with {@code MongoTemplate} to define in which type of transactions to
+ * participate if any.
  *
  * @author Christoph Strobl
  * @author Mark Paluch
  * @since 2.1
+ * @see MongoTemplate#setSessionSynchronization(SessionSynchronization)
+ * @see MongoDatabaseUtils#getDatabase(MongoDatabaseFactory, SessionSynchronization)
+ * @see ReactiveMongoTemplate#setSessionSynchronization(SessionSynchronization)
+ * @see ReactiveMongoDatabaseUtils#getDatabase(ReactiveMongoDatabaseFactory, SessionSynchronization)
  */
 public enum SessionSynchronization {
 
@@ -34,5 +41,12 @@ public enum SessionSynchronization {
 	/**
 	 * Synchronize with native MongoDB transactions initiated via {@link MongoTransactionManager}.
 	 */
-	ON_ACTUAL_TRANSACTION;
+	ON_ACTUAL_TRANSACTION,
+
+	/**
+	 * Do not participate in ongoing transactions.
+	 *
+	 * @since 3.2.5
+	 */
+	NEVER;
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/SpringDataMongoDB.java

@@ -48,7 +48,7 @@ public class SpringDataMongoDB {
 
 	/**
 	 * Fetches the "Implementation-Version" manifest attribute from the jar file.
-	 * <p />
+	 * <br />
 	 * Note that some ClassLoaders do not expose the package metadata, hence this class might not be able to determine the
 	 * version in all environments. In this case the current Major version is returned as a fallback.
 	 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/config/MongoConfigurationSupport.java

@@ -26,7 +26,6 @@ import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider;
 import org.springframework.core.convert.converter.Converter;
 import org.springframework.core.type.filter.AnnotationTypeFilter;
-import org.springframework.data.annotation.Persistent;
 import org.springframework.data.convert.CustomConversions;
 import org.springframework.data.mapping.model.CamelCaseAbbreviatingFieldNamingStrategy;
 import org.springframework.data.mapping.model.FieldNamingStrategy;
@@ -140,8 +139,7 @@ public abstract class MongoConfigurationSupport {
 	}
 
 	/**
-	 * Scans the given base package for entities, i.e. MongoDB specific types annotated with {@link Document} and
-	 * {@link Persistent}.
+	 * Scans the given base package for entities, i.e. MongoDB specific types annotated with {@link Document}.
 	 *
 	 * @param basePackage must not be {@literal null}.
 	 * @return
@@ -161,7 +159,6 @@ public abstract class MongoConfigurationSupport {
 			ClassPathScanningCandidateComponentProvider componentProvider = new ClassPathScanningCandidateComponentProvider(
 					false);
 			componentProvider.addIncludeFilter(new AnnotationTypeFilter(Document.class));
-			componentProvider.addIncludeFilter(new AnnotationTypeFilter(Persistent.class));
 
 			for (BeanDefinition candidate : componentProvider.findCandidateComponents(basePackage)) {
 
@@ -175,8 +172,7 @@ public abstract class MongoConfigurationSupport {
 
 	/**
 	 * Configures whether to abbreviate field names for domain objects by configuring a
-	 * {@link CamelCaseAbbreviatingFieldNamingStrategy} on the {@link MongoMappingContext} instance created. For advanced
-	 * customization needs, consider overriding {@link #mappingMongoConverter()}.
+	 * {@link CamelCaseAbbreviatingFieldNamingStrategy} on the {@link MongoMappingContext} instance created.
 	 *
 	 * @return
 	 */

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/config/MongoParsingUtils.java

@@ -22,9 +22,12 @@ import java.util.Map;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.config.CustomEditorConfigurer;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
+import org.springframework.beans.factory.support.BeanDefinitionValidationException;
 import org.springframework.beans.factory.support.ManagedMap;
 import org.springframework.beans.factory.xml.BeanDefinitionParser;
 import org.springframework.data.mongodb.core.MongoClientSettingsFactoryBean;
+import org.springframework.data.mongodb.core.MongoServerApiFactoryBean;
+import org.springframework.util.StringUtils;
 import org.springframework.util.xml.DomUtils;
 import org.w3c.dom.Element;
 
@@ -112,6 +115,20 @@ abstract class MongoParsingUtils {
 		// Field level encryption
 		setPropertyReference(clientOptionsDefBuilder, settingsElement, "encryption-settings-ref", "autoEncryptionSettings");
 
+		// ServerAPI
+		if (StringUtils.hasText(settingsElement.getAttribute("server-api-version"))) {
+
+			MongoServerApiFactoryBean serverApiFactoryBean = new MongoServerApiFactoryBean();
+			serverApiFactoryBean.setVersion(settingsElement.getAttribute("server-api-version"));
+			try {
+				clientOptionsDefBuilder.addPropertyValue("serverApi", serverApiFactoryBean.getObject());
+			} catch (Exception exception) {
+				throw new BeanDefinitionValidationException("Non parsable server-api.", exception);
+			}
+		} else {
+			setPropertyReference(clientOptionsDefBuilder, settingsElement, "server-api-ref", "serverApi");
+		}
+
 		// and the rest
 
 		mongoClientBuilder.addPropertyValue("mongoClientSettings", clientOptionsDefBuilder.getBeanDefinition());

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/config/PersistentEntitiesFactoryBean.java

@@ -28,7 +28,7 @@ import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
  * @author Christoph Strobl
  * @since 3.1
  */
-class PersistentEntitiesFactoryBean implements FactoryBean<PersistentEntities> {
+public class PersistentEntitiesFactoryBean implements FactoryBean<PersistentEntities> {
 
 	private final MappingMongoConverter converter;
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/AggregationUtil.java

@@ -27,6 +27,7 @@ import org.springframework.data.mongodb.core.aggregation.Aggregation;
 import org.springframework.data.mongodb.core.aggregation.AggregationOperation;
 import org.springframework.data.mongodb.core.aggregation.AggregationOperationContext;
 import org.springframework.data.mongodb.core.aggregation.AggregationOptions;
+import org.springframework.data.mongodb.core.aggregation.AggregationOptions.DomainTypeMapping;
 import org.springframework.data.mongodb.core.aggregation.CountOperation;
 import org.springframework.data.mongodb.core.aggregation.RelaxedTypeBasedAggregationOperationContext;
 import org.springframework.data.mongodb.core.aggregation.TypeBasedAggregationOperationContext;
@@ -36,6 +37,7 @@ import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.data.mongodb.core.query.CriteriaDefinition;
 import org.springframework.data.mongodb.core.query.Query;
+import org.springframework.data.util.Lazy;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
@@ -52,41 +54,46 @@ class AggregationUtil {
 
 	QueryMapper queryMapper;
 	MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext;
+	Lazy<AggregationOperationContext> untypedMappingContext;
 
 	AggregationUtil(QueryMapper queryMapper,
 			MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext) {
 
 		this.queryMapper = queryMapper;
 		this.mappingContext = mappingContext;
+		this.untypedMappingContext = Lazy
+				.of(() -> new RelaxedTypeBasedAggregationOperationContext(Object.class, mappingContext, queryMapper));
 	}
 
-	/**
-	 * Prepare the {@link AggregationOperationContext} for a given aggregation by either returning the context itself it
-	 * is not {@literal null}, create a {@link TypeBasedAggregationOperationContext} if the aggregation contains type
-	 * information (is a {@link TypedAggregation}) or use the {@link Aggregation#DEFAULT_CONTEXT}.
-	 *
-	 * @param aggregation must not be {@literal null}.
-	 * @param context can be {@literal null}.
-	 * @return the root {@link AggregationOperationContext} to use.
-	 */
-	AggregationOperationContext prepareAggregationContext(Aggregation aggregation,
-			@Nullable AggregationOperationContext context) {
+	AggregationOperationContext createAggregationContext(Aggregation aggregation, @Nullable Class<?> inputType) {
 
-		if (context != null) {
-			return context;
+		DomainTypeMapping domainTypeMapping = aggregation.getOptions().getDomainTypeMapping();
+
+		if (domainTypeMapping == DomainTypeMapping.NONE) {
+			return Aggregation.DEFAULT_CONTEXT;
 		}
 
 		if (!(aggregation instanceof TypedAggregation)) {
-			return new RelaxedTypeBasedAggregationOperationContext(Object.class, mappingContext, queryMapper);
-		}
 
-		Class<?> inputType = ((TypedAggregation) aggregation).getInputType();
+			if(inputType == null) {
+				return untypedMappingContext.get();
+			}
+
+			if (domainTypeMapping == DomainTypeMapping.STRICT
+					&& !aggregation.getPipeline().containsUnionWith()) {
+				return new TypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper);
+			}
 
-		if (aggregation.getPipeline().containsUnionWith()) {
 			return new RelaxedTypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper);
 		}
 
-		return new TypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper);
+		inputType = ((TypedAggregation<?>) aggregation).getInputType();
+		if (domainTypeMapping == DomainTypeMapping.STRICT
+				&& !aggregation.getPipeline().containsUnionWith()) {
+			return new TypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper);
+		}
+
+		return new RelaxedTypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper);
 	}
 
 	/**
@@ -125,53 +132,6 @@ class AggregationUtil {
 		return command;
 	}
 
-	/**
-	 * Create a {@code $count} aggregation for {@link Query} and optionally a {@link Class entity class}.
-	 *
-	 * @param query must not be {@literal null}.
-	 * @param entityClass can be {@literal null} if the {@link Query} object is empty.
-	 * @return the {@link Aggregation} pipeline definition to run a {@code $count} aggregation.
-	 */
-	Aggregation createCountAggregation(Query query, @Nullable Class<?> entityClass) {
-
-		List<AggregationOperation> pipeline = computeCountAggregationPipeline(query, entityClass);
-
-		Aggregation aggregation = entityClass != null ? Aggregation.newAggregation(entityClass, pipeline)
-				: Aggregation.newAggregation(pipeline);
-		aggregation.withOptions(AggregationOptions.builder().collation(query.getCollation().orElse(null)).build());
-
-		return aggregation;
-	}
-
-	private List<AggregationOperation> computeCountAggregationPipeline(Query query, @Nullable Class<?> entityType) {
-
-		CountOperation count = Aggregation.count().as("totalEntityCount");
-		if (query.getQueryObject().isEmpty()) {
-			return Collections.singletonList(count);
-		}
-
-		Assert.notNull(entityType, "Entity type must not be null!");
-
-		Document mappedQuery = queryMapper.getMappedObject(query.getQueryObject(),
-				mappingContext.getPersistentEntity(entityType));
-
-		CriteriaDefinition criteria = new CriteriaDefinition() {
-
-			@Override
-			public Document getCriteriaObject() {
-				return mappedQuery;
-			}
-
-			@Nullable
-			@Override
-			public String getKey() {
-				return null;
-			}
-		};
-
-		return Arrays.asList(Aggregation.match(criteria), count);
-	}
-
 	private List<Document> mapAggregationPipeline(List<Document> pipeline) {
 
 		return pipeline.stream().map(val -> queryMapper.getMappedObject(val, Optional.empty()))

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ChangeStreamOptions.java

@@ -242,13 +242,13 @@ public class ChangeStreamOptions {
 
 		/**
 		 * Set the filter to apply.
-		 * <p/>
+		 * <br />
 		 * Fields on aggregation expression root level are prefixed to map to fields contained in
 		 * {@link ChangeStreamDocument#getFullDocument() fullDocument}. However {@literal operationType}, {@literal ns},
 		 * {@literal documentKey} and {@literal fullDocument} are reserved words that will be omitted, and therefore taken
 		 * as given, during the mapping procedure. You may want to have a look at the
 		 * <a href="https://docs.mongodb.com/manual/reference/change-events/">structure of Change Events</a>.
-		 * <p/>
+		 * <br />
 		 * Use {@link org.springframework.data.mongodb.core.aggregation.TypedAggregation} to ensure filter expressions are
 		 * mapped to domain type fields.
 		 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/CollectionOptions.java

@@ -17,8 +17,11 @@ package org.springframework.data.mongodb.core;
 
 import java.util.Optional;
 
+import org.springframework.data.mongodb.core.mapping.Field;
 import org.springframework.data.mongodb.core.query.Collation;
 import org.springframework.data.mongodb.core.schema.MongoJsonSchema;
+import org.springframework.data.mongodb.core.timeseries.Granularity;
+import org.springframework.data.mongodb.core.timeseries.GranularityDefinition;
 import org.springframework.data.mongodb.core.validation.Validator;
 import org.springframework.data.util.Optionals;
 import org.springframework.lang.Nullable;
@@ -42,6 +45,7 @@ public class CollectionOptions {
 	private @Nullable Boolean capped;
 	private @Nullable Collation collation;
 	private ValidationOptions validationOptions;
+	private @Nullable TimeSeriesOptions timeSeriesOptions;
 
 	/**
 	 * Constructs a new <code>CollectionOptions</code> instance.
@@ -54,17 +58,19 @@ public class CollectionOptions {
 	 */
 	@Deprecated
 	public CollectionOptions(@Nullable Long size, @Nullable Long maxDocuments, @Nullable Boolean capped) {
-		this(size, maxDocuments, capped, null, ValidationOptions.none());
+		this(size, maxDocuments, capped, null, ValidationOptions.none(), null);
 	}
 
 	private CollectionOptions(@Nullable Long size, @Nullable Long maxDocuments, @Nullable Boolean capped,
-			@Nullable Collation collation, ValidationOptions validationOptions) {
+			@Nullable Collation collation, ValidationOptions validationOptions,
+			@Nullable TimeSeriesOptions timeSeriesOptions) {
 
 		this.maxDocuments = maxDocuments;
 		this.size = size;
 		this.capped = capped;
 		this.collation = collation;
 		this.validationOptions = validationOptions;
+		this.timeSeriesOptions = timeSeriesOptions;
 	}
 
 	/**
@@ -78,7 +84,7 @@ public class CollectionOptions {
 
 		Assert.notNull(collation, "Collation must not be null!");
 
-		return new CollectionOptions(null, null, null, collation, ValidationOptions.none());
+		return new CollectionOptions(null, null, null, collation, ValidationOptions.none(), null);
 	}
 
 	/**
@@ -88,7 +94,21 @@ public class CollectionOptions {
 	 * @since 2.0
 	 */
 	public static CollectionOptions empty() {
-		return new CollectionOptions(null, null, null, null, ValidationOptions.none());
+		return new CollectionOptions(null, null, null, null, ValidationOptions.none(), null);
+	}
+
+	/**
+	 * Quick way to set up {@link CollectionOptions} for a Time Series collection. For more advanced settings use
+	 * {@link #timeSeries(TimeSeriesOptions)}.
+	 *
+	 * @param timeField The name of the property which contains the date in each time series document. Must not be
+	 *          {@literal null}.
+	 * @return new instance of {@link CollectionOptions}.
+	 * @see #timeSeries(TimeSeriesOptions)
+	 * @since 3.3
+	 */
+	public static CollectionOptions timeSeries(String timeField) {
+		return empty().timeSeries(TimeSeriesOptions.timeSeries(timeField));
 	}
 
 	/**
@@ -99,7 +119,7 @@ public class CollectionOptions {
 	 * @since 2.0
 	 */
 	public CollectionOptions capped() {
-		return new CollectionOptions(size, maxDocuments, true, collation, validationOptions);
+		return new CollectionOptions(size, maxDocuments, true, collation, validationOptions, null);
 	}
 
 	/**
@@ -110,7 +130,7 @@ public class CollectionOptions {
 	 * @since 2.0
 	 */
 	public CollectionOptions maxDocuments(long maxDocuments) {
-		return new CollectionOptions(size, maxDocuments, capped, collation, validationOptions);
+		return new CollectionOptions(size, maxDocuments, capped, collation, validationOptions, timeSeriesOptions);
 	}
 
 	/**
@@ -121,7 +141,7 @@ public class CollectionOptions {
 	 * @since 2.0
 	 */
 	public CollectionOptions size(long size) {
-		return new CollectionOptions(size, maxDocuments, capped, collation, validationOptions);
+		return new CollectionOptions(size, maxDocuments, capped, collation, validationOptions, timeSeriesOptions);
 	}
 
 	/**
@@ -132,7 +152,7 @@ public class CollectionOptions {
 	 * @since 2.0
 	 */
 	public CollectionOptions collation(@Nullable Collation collation) {
-		return new CollectionOptions(size, maxDocuments, capped, collation, validationOptions);
+		return new CollectionOptions(size, maxDocuments, capped, collation, validationOptions, timeSeriesOptions);
 	}
 
 	/**
@@ -252,7 +272,20 @@ public class CollectionOptions {
 	public CollectionOptions validation(ValidationOptions validationOptions) {
 
 		Assert.notNull(validationOptions, "ValidationOptions must not be null!");
-		return new CollectionOptions(size, maxDocuments, capped, collation, validationOptions);
+		return new CollectionOptions(size, maxDocuments, capped, collation, validationOptions, timeSeriesOptions);
+	}
+
+	/**
+	 * Create new {@link CollectionOptions} with the given {@link TimeSeriesOptions}.
+	 *
+	 * @param timeSeriesOptions must not be {@literal null}.
+	 * @return new instance of {@link CollectionOptions}.
+	 * @since 3.3
+	 */
+	public CollectionOptions timeSeries(TimeSeriesOptions timeSeriesOptions) {
+
+		Assert.notNull(timeSeriesOptions, "TimeSeriesOptions must not be null!");
+		return new CollectionOptions(size, maxDocuments, capped, collation, validationOptions, timeSeriesOptions);
 	}
 
 	/**
@@ -303,6 +336,16 @@ public class CollectionOptions {
 		return validationOptions.isEmpty() ? Optional.empty() : Optional.of(validationOptions);
 	}
 
+	/**
+	 * Get the {@link TimeSeriesOptions} if available.
+	 *
+	 * @return {@link Optional#empty()} if not specified.
+	 * @since 3.3
+	 */
+	public Optional<TimeSeriesOptions> getTimeSeriesOptions() {
+		return Optional.ofNullable(timeSeriesOptions);
+	}
+
 	/**
 	 * Encapsulation of ValidationOptions options.
 	 *
@@ -385,7 +428,7 @@ public class CollectionOptions {
 		/**
 		 * Get the {@code validationAction} to perform.
 		 *
-		 * @return @return {@link Optional#empty()} if not set.
+		 * @return {@link Optional#empty()} if not set.
 		 */
 		public Optional<ValidationAction> getValidationAction() {
 			return Optional.ofNullable(validationAction);
@@ -398,4 +441,89 @@ public class CollectionOptions {
 			return !Optionals.isAnyPresent(getValidator(), getValidationAction(), getValidationLevel());
 		}
 	}
+
+	/**
+	 * Options applicable to Time Series collections.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 * @see <a href=
+	 *      "https://docs.mongodb.com/manual/core/timeseries-collections">https://docs.mongodb.com/manual/core/timeseries-collections</a>
+	 */
+	public static class TimeSeriesOptions {
+
+		private final String timeField;
+
+		private @Nullable final String metaField;
+
+		private final GranularityDefinition granularity;
+
+		private TimeSeriesOptions(String timeField, @Nullable String metaField, GranularityDefinition granularity) {
+
+			Assert.hasText(timeField, "Time field must not be empty or null!");
+
+			this.timeField = timeField;
+			this.metaField = metaField;
+			this.granularity = granularity;
+		}
+
+		/**
+		 * Create a new instance of {@link TimeSeriesOptions} using the given field as its {@literal timeField}. The one,
+		 * that contains the date in each time series document. <br />
+		 * {@link Field#name() Annotated fieldnames} will be considered during the mapping process.
+		 *
+		 * @param timeField must not be {@literal null}.
+		 * @return new instance of {@link TimeSeriesOptions}.
+		 */
+		public static TimeSeriesOptions timeSeries(String timeField) {
+			return new TimeSeriesOptions(timeField, null, Granularity.DEFAULT);
+		}
+
+		/**
+		 * Set the name of the field which contains metadata in each time series document. Should not be the {@literal id}
+		 * nor {@link TimeSeriesOptions#timeSeries(String)} timeField} nor point to an {@literal array} or
+		 * {@link java.util.Collection}. <br />
+		 * {@link Field#name() Annotated fieldnames} will be considered during the mapping process.
+		 *
+		 * @param metaField must not be {@literal null}.
+		 * @return new instance of {@link TimeSeriesOptions}.
+		 */
+		public TimeSeriesOptions metaField(String metaField) {
+			return new TimeSeriesOptions(timeField, metaField, granularity);
+		}
+
+		/**
+		 * Select the {@link GranularityDefinition} parameter to define how data in the time series collection is organized.
+		 * Select one that is closest to the time span between incoming measurements.
+		 *
+		 * @return new instance of {@link TimeSeriesOptions}.
+		 * @see Granularity
+		 */
+		public TimeSeriesOptions granularity(GranularityDefinition granularity) {
+			return new TimeSeriesOptions(timeField, metaField, granularity);
+		}
+
+		/**
+		 * @return never {@literal null}.
+		 */
+		public String getTimeField() {
+			return timeField;
+		}
+
+		/**
+		 * @return can be {@literal null}. Might be an {@literal empty} {@link String} as well, so maybe check via
+		 *         {@link org.springframework.util.StringUtils#hasText(String)}.
+		 */
+		@Nullable
+		public String getMetaField() {
+			return metaField;
+		}
+
+		/**
+		 * @return never {@literal null}.
+		 */
+		public GranularityDefinition getGranularity() {
+			return granularity;
+		}
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/DefaultIndexOperationsProvider.java

@@ -47,7 +47,7 @@ class DefaultIndexOperationsProvider implements IndexOperationsProvider {
 	 * @see org.springframework.data.mongodb.core.index.IndexOperationsProvider#reactiveIndexOps(java.lang.String)
 	 */
 	@Override
-	public IndexOperations indexOps(String collectionName) {
-		return new DefaultIndexOperations(mongoDbFactory, collectionName, mapper);
+	public IndexOperations indexOps(String collectionName, Class<?> type) {
+		return new DefaultIndexOperations(mongoDbFactory, collectionName, mapper, type);
 	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/EncryptionAlgorithms.java

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.core;
+
+/**
+ * Encryption algorithms supported by MongoDB Client Side Field Level Encryption.
+ *
+ * @author Christoph Strobl
+ * @since 3.3
+ */
+public final class EncryptionAlgorithms {
+
+	public static final String AEAD_AES_256_CBC_HMAC_SHA_512_Deterministic = "AEAD_AES_256_CBC_HMAC_SHA_512-Deterministic";
+	public static final String AEAD_AES_256_CBC_HMAC_SHA_512_Random = "AEAD_AES_256_CBC_HMAC_SHA_512-Random";
+
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/EntityOperations.java

@@ -16,6 +16,7 @@
 package org.springframework.data.mongodb.core;
 
 import java.util.Collection;
+import java.util.Iterator;
 import java.util.Map;
 import java.util.Optional;
 
@@ -28,18 +29,23 @@ import org.springframework.data.mapping.PersistentEntity;
 import org.springframework.data.mapping.PersistentPropertyAccessor;
 import org.springframework.data.mapping.context.MappingContext;
 import org.springframework.data.mapping.model.ConvertingPropertyAccessor;
+import org.springframework.data.mongodb.core.CollectionOptions.TimeSeriesOptions;
 import org.springframework.data.mongodb.core.convert.MongoWriter;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.data.mongodb.core.mapping.MongoSimpleTypes;
+import org.springframework.data.mongodb.core.mapping.TimeSeries;
 import org.springframework.data.mongodb.core.query.Collation;
 import org.springframework.data.mongodb.core.query.Criteria;
 import org.springframework.data.mongodb.core.query.Query;
+import org.springframework.data.mongodb.core.timeseries.Granularity;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
+import org.springframework.util.ObjectUtils;
+import org.springframework.util.StringUtils;
 
 /**
  * Common operations performed on an entity in the context of it's mapping metadata.
@@ -107,6 +113,20 @@ class EntityOperations {
 		return AdaptibleMappedEntity.of(entity, context, conversionService);
 	}
 
+	/**
+	 * @param source can be {@literal null}.
+	 * @return {@literal true} if the given value is an {@literal array}, {@link Collection} or {@link Iterator}.
+	 * @since 3.2
+	 */
+	static boolean isCollectionLike(@Nullable Object source) {
+
+		if (source == null) {
+			return false;
+		}
+
+		return ObjectUtils.isArray(source) || source instanceof Collection || source instanceof Iterator;
+	}
+
 	/**
 	 * @param entityClass should not be null.
 	 * @return the {@link MongoPersistentEntity#getCollection() collection name}.
@@ -762,6 +782,24 @@ class EntityOperations {
 		 * @return
 		 */
 		Optional<Collation> getCollation(Query query);
+
+		/**
+		 * Derive the applicable {@link CollectionOptions} for the given type.
+		 *
+		 * @return never {@literal null}.
+		 * @since 3.3
+		 */
+		CollectionOptions getCollectionOptions();
+
+		/**
+		 * Map the fields of a given {@link TimeSeriesOptions} against the target domain type to consider potentially
+		 * annotated field names.
+		 *
+		 * @param options must not be {@literal null}.
+		 * @return never {@literal null}.
+		 * @since 3.3
+		 */
+		TimeSeriesOptions mapTimeSeriesOptions(TimeSeriesOptions options);
 	}
 
 	/**
@@ -801,6 +839,16 @@ class EntityOperations {
 
 			return query.getCollation();
 		}
+
+		@Override
+		public CollectionOptions getCollectionOptions() {
+			return CollectionOptions.empty();
+		}
+
+		@Override
+		public TimeSeriesOptions mapTimeSeriesOptions(TimeSeriesOptions options) {
+			return options;
+		}
 	}
 
 	/**
@@ -838,6 +886,58 @@ class EntityOperations {
 
 			return Optional.ofNullable(entity.getCollation());
 		}
+
+		@Override
+		public CollectionOptions getCollectionOptions() {
+
+			CollectionOptions collectionOptions = CollectionOptions.empty();
+			if (entity.hasCollation()) {
+				collectionOptions = collectionOptions.collation(entity.getCollation());
+			}
+
+			if (entity.isAnnotationPresent(TimeSeries.class)) {
+
+				TimeSeries timeSeries = entity.getRequiredAnnotation(TimeSeries.class);
+
+				if (entity.getPersistentProperty(timeSeries.timeField()) == null) {
+					throw new MappingException(String.format("Time series field '%s' does not exist in type %s",
+							timeSeries.timeField(), entity.getName()));
+				}
+
+				TimeSeriesOptions options = TimeSeriesOptions.timeSeries(timeSeries.timeField());
+				if (StringUtils.hasText(timeSeries.metaField())) {
+
+					if (entity.getPersistentProperty(timeSeries.metaField()) == null) {
+						throw new MappingException(
+								String.format("Meta field '%s' does not exist in type %s", timeSeries.metaField(), entity.getName()));
+					}
+
+					options = options.metaField(timeSeries.metaField());
+				}
+				if (!Granularity.DEFAULT.equals(timeSeries.granularity())) {
+					options = options.granularity(timeSeries.granularity());
+				}
+				collectionOptions = collectionOptions.timeSeries(options);
+			}
+
+			return collectionOptions;
+		}
+
+		@Override
+		public TimeSeriesOptions mapTimeSeriesOptions(TimeSeriesOptions source) {
+
+			TimeSeriesOptions target = TimeSeriesOptions.timeSeries(mappedNameOrDefault(source.getTimeField()));
+
+			if (StringUtils.hasText(source.getMetaField())) {
+				target = target.metaField(mappedNameOrDefault(source.getMetaField()));
+			}
+			return target.granularity(source.getGranularity());
+		}
+
+		private String mappedNameOrDefault(String name) {
+			MongoPersistentProperty persistentProperty = entity.getPersistentProperty(name);
+			return persistentProperty != null ? persistentProperty.getFieldName() : name;
+		}
 	}
 
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ExecutableFindOperation.java

@@ -125,6 +125,11 @@ public interface ExecutableFindOperation {
 
 		/**
 		 * Get the number of matching elements.
+		 * <br />
+		 * This method uses an {@link com.mongodb.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions) aggregation
+		 * execution} even for empty {@link Query queries} which may have an impact on performance, but guarantees shard,
+		 * session and transaction compliance. In case an inaccurate count satisfies the applications needs use
+		 * {@link MongoOperations#estimatedCount(String)} for empty queries instead.
 		 *
 		 * @return total number of matching elements.
 		 */

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ExecutableUpdateOperation.java

@@ -89,7 +89,7 @@ public interface ExecutableUpdateOperation {
 
 	/**
 	 * Trigger
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * execution by calling one of the terminating methods.
 	 *
 	 * @author Mark Paluch

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/FindAndReplaceOptions.java

@@ -17,7 +17,7 @@ package org.springframework.data.mongodb.core;
 
 /**
  * Options for
- * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>.
+ * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>.
  * <br />
  * Defaults to
  * <dl>

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/IndexConverters.java

@@ -115,6 +115,10 @@ abstract class IndexConverters {
 				ops = ops.collation(fromDocument(indexOptions.get("collation", Document.class)));
 			}
 
+			if (indexOptions.containsKey("wildcardProjection")) {
+				ops.wildcardProjection(indexOptions.get("wildcardProjection", Document.class));
+			}
+
 			return ops;
 		};
 	}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MappedDocument.java

@@ -156,5 +156,14 @@ public class MappedDocument {
 		public List<ArrayFilter> getArrayFilters() {
 			return delegate.getArrayFilters();
 		}
+
+		/*
+		 * (non-Javadoc)
+		 * @see org.springframework.data.mongodb.core.query.UpdateDefinition#hasArrayFilters()
+		 */
+		@Override
+		public boolean hasArrayFilters() {
+			return delegate.hasArrayFilters();
+		}
 	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MappingMongoJsonSchemaCreator.java

@@ -20,13 +20,20 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.EnumSet;
 import java.util.List;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+import org.bson.Document;
 
 import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.mapping.context.MappingContext;
 import org.springframework.data.mongodb.core.convert.MongoConverter;
+import org.springframework.data.mongodb.core.mapping.Encrypted;
 import org.springframework.data.mongodb.core.mapping.Field;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
+import org.springframework.data.mongodb.core.schema.IdentifiableJsonSchemaProperty.ArrayJsonSchemaProperty;
+import org.springframework.data.mongodb.core.schema.IdentifiableJsonSchemaProperty.EncryptedJsonSchemaProperty;
 import org.springframework.data.mongodb.core.schema.IdentifiableJsonSchemaProperty.ObjectJsonSchemaProperty;
 import org.springframework.data.mongodb.core.schema.JsonSchemaObject;
 import org.springframework.data.mongodb.core.schema.JsonSchemaObject.Type;
@@ -34,10 +41,12 @@ import org.springframework.data.mongodb.core.schema.JsonSchemaProperty;
 import org.springframework.data.mongodb.core.schema.MongoJsonSchema;
 import org.springframework.data.mongodb.core.schema.MongoJsonSchema.MongoJsonSchemaBuilder;
 import org.springframework.data.mongodb.core.schema.TypedJsonSchemaObject;
+import org.springframework.data.util.ClassTypeInformation;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
+import org.springframework.util.StringUtils;
 
 /**
  * {@link MongoJsonSchemaCreator} implementation using both {@link MongoConverter} and {@link MappingContext} to obtain
@@ -52,6 +61,7 @@ class MappingMongoJsonSchemaCreator implements MongoJsonSchemaCreator {
 
 	private final MongoConverter converter;
 	private final MappingContext<MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext;
+	private final Predicate<JsonSchemaPropertyContext> filter;
 
 	/**
 	 * Create a new instance of {@link MappingMongoJsonSchemaCreator}.
@@ -61,10 +71,24 @@ class MappingMongoJsonSchemaCreator implements MongoJsonSchemaCreator {
 	@SuppressWarnings("unchecked")
 	MappingMongoJsonSchemaCreator(MongoConverter converter) {
 
+		this(converter, (MappingContext<MongoPersistentEntity<?>, MongoPersistentProperty>) converter.getMappingContext(),
+				(property) -> true);
+	}
+
+	@SuppressWarnings("unchecked")
+	MappingMongoJsonSchemaCreator(MongoConverter converter,
+			MappingContext<MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext,
+			Predicate<JsonSchemaPropertyContext> filter) {
+
 		Assert.notNull(converter, "Converter must not be null!");
 		this.converter = converter;
-		this.mappingContext = (MappingContext<MongoPersistentEntity<?>, MongoPersistentProperty>) converter
-				.getMappingContext();
+		this.mappingContext = mappingContext;
+		this.filter = filter;
+	}
+
+	@Override
+	public MongoJsonSchemaCreator filter(Predicate<JsonSchemaPropertyContext> filter) {
+		return new MappingMongoJsonSchemaCreator(converter, mappingContext, filter);
 	}
 
 	/*
@@ -77,11 +101,29 @@ class MappingMongoJsonSchemaCreator implements MongoJsonSchemaCreator {
 		MongoPersistentEntity<?> entity = mappingContext.getRequiredPersistentEntity(type);
 		MongoJsonSchemaBuilder schemaBuilder = MongoJsonSchema.builder();
 
+		{
+			Encrypted encrypted = entity.findAnnotation(Encrypted.class);
+			if (encrypted != null) {
+
+				Document encryptionMetadata = new Document();
+
+				Collection<Object> encryptionKeyIds = entity.getEncryptionKeyIds();
+				if (!CollectionUtils.isEmpty(encryptionKeyIds)) {
+					encryptionMetadata.append("keyId", encryptionKeyIds);
+				}
+
+				if (StringUtils.hasText(encrypted.algorithm())) {
+					encryptionMetadata.append("algorithm", encrypted.algorithm());
+				}
+
+				schemaBuilder.encryptionMetadata(encryptionMetadata);
+			}
+		}
+
 		List<JsonSchemaProperty> schemaProperties = computePropertiesForEntity(Collections.emptyList(), entity);
 		schemaBuilder.properties(schemaProperties.toArray(new JsonSchemaProperty[0]));
 
 		return schemaBuilder.build();
-
 	}
 
 	private List<JsonSchemaProperty> computePropertiesForEntity(List<MongoPersistentProperty> path,
@@ -93,6 +135,11 @@ class MappingMongoJsonSchemaCreator implements MongoJsonSchemaCreator {
 
 			List<MongoPersistentProperty> currentPath = new ArrayList<>(path);
 
+			if (!filter.test(new PropertyContext(
+					currentPath.stream().map(PersistentProperty::getName).collect(Collectors.joining(".")), nested))) {
+				continue;
+			}
+
 			if (path.contains(nested)) { // cycle guard
 				schemaProperties.add(createSchemaProperty(computePropertyFieldName(CollectionUtils.lastElement(currentPath)),
 						Object.class, false));
@@ -114,21 +161,88 @@ class MappingMongoJsonSchemaCreator implements MongoJsonSchemaCreator {
 		Class<?> rawTargetType = computeTargetType(property); // target type before conversion
 		Class<?> targetType = converter.getTypeMapper().getWriteTargetTypeFor(rawTargetType); // conversion target type
 
-		if (property.isEntity() && ObjectUtils.nullSafeEquals(rawTargetType, targetType)) {
+		if (!isCollection(property) && property.isEntity() && ObjectUtils.nullSafeEquals(rawTargetType, targetType)) {
 			return createObjectSchemaPropertyForEntity(path, property, required);
 		}
 
 		String fieldName = computePropertyFieldName(property);
 
-		if (property.isCollectionLike()) {
-			return createSchemaProperty(fieldName, targetType, required);
+		JsonSchemaProperty schemaProperty;
+		if (isCollection(property)) {
+			schemaProperty = createArraySchemaProperty(fieldName, property, required);
 		} else if (property.isMap()) {
-			return createSchemaProperty(fieldName, Type.objectType(), required);
+			schemaProperty = createSchemaProperty(fieldName, Type.objectType(), required);
 		} else if (ClassUtils.isAssignable(Enum.class, targetType)) {
-			return createEnumSchemaProperty(fieldName, targetType, required);
+			schemaProperty = createEnumSchemaProperty(fieldName, targetType, required);
+		} else {
+			schemaProperty = createSchemaProperty(fieldName, targetType, required);
 		}
 
-		return createSchemaProperty(fieldName, targetType, required);
+		return applyEncryptionDataIfNecessary(property, schemaProperty);
+	}
+
+	private JsonSchemaProperty createArraySchemaProperty(String fieldName, MongoPersistentProperty property,
+			boolean required) {
+
+		ArrayJsonSchemaProperty schemaProperty = JsonSchemaProperty.array(fieldName);
+
+		if (isSpecificType(property)) {
+			schemaProperty = potentiallyEnhanceArraySchemaProperty(property, schemaProperty);
+		}
+
+		return createPotentiallyRequiredSchemaProperty(schemaProperty, required);
+	}
+
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	private ArrayJsonSchemaProperty potentiallyEnhanceArraySchemaProperty(MongoPersistentProperty property,
+			ArrayJsonSchemaProperty schemaProperty) {
+
+		MongoPersistentEntity<?> persistentEntity = mappingContext
+				.getPersistentEntity(property.getTypeInformation().getRequiredComponentType());
+
+		if (persistentEntity != null) {
+
+			List<JsonSchemaProperty> nestedProperties = computePropertiesForEntity(Collections.emptyList(), persistentEntity);
+
+			if (nestedProperties.isEmpty()) {
+				return schemaProperty;
+			}
+
+			return schemaProperty
+					.items(JsonSchemaObject.object().properties(nestedProperties.toArray(new JsonSchemaProperty[0])));
+		}
+
+		if (ClassUtils.isAssignable(Enum.class, property.getActualType())) {
+
+			List<Object> possibleValues = getPossibleEnumValues((Class<Enum>) property.getActualType());
+
+			return schemaProperty
+					.items(createSchemaObject(computeTargetType(property.getActualType(), possibleValues), possibleValues));
+		}
+
+		return schemaProperty.items(JsonSchemaObject.of(property.getActualType()));
+	}
+
+	private boolean isSpecificType(MongoPersistentProperty property) {
+		return !ClassTypeInformation.OBJECT.equals(property.getTypeInformation().getActualType());
+	}
+
+	private JsonSchemaProperty applyEncryptionDataIfNecessary(MongoPersistentProperty property,
+			JsonSchemaProperty schemaProperty) {
+
+		Encrypted encrypted = property.findAnnotation(Encrypted.class);
+		if (encrypted == null) {
+			return schemaProperty;
+		}
+
+		EncryptedJsonSchemaProperty enc = new EncryptedJsonSchemaProperty(schemaProperty);
+		if (StringUtils.hasText(encrypted.algorithm())) {
+			enc = enc.algorithm(encrypted.algorithm());
+		}
+		if (!ObjectUtils.isEmpty(encrypted.keyId())) {
+			enc = enc.keys(property.getEncryptionKeyIds());
+		}
+		return enc;
 	}
 
 	private JsonSchemaProperty createObjectSchemaPropertyForEntity(List<MongoPersistentProperty> path,
@@ -142,15 +256,12 @@ class MappingMongoJsonSchemaCreator implements MongoJsonSchemaCreator {
 				target.properties(nestedProperties.toArray(new JsonSchemaProperty[0])), required);
 	}
 
+	@SuppressWarnings({ "unchecked", "rawtypes" })
 	private JsonSchemaProperty createEnumSchemaProperty(String fieldName, Class<?> targetType, boolean required) {
 
-		List<Object> possibleValues = new ArrayList<>();
+		List<Object> possibleValues = getPossibleEnumValues((Class<Enum>) targetType);
 
-		for (Object enumValue : EnumSet.allOf((Class) targetType)) {
-			possibleValues.add(converter.convertToMongoType(enumValue));
-		}
-
-		targetType = possibleValues.isEmpty() ? targetType : possibleValues.iterator().next().getClass();
+		targetType = computeTargetType(targetType, possibleValues);
 		return createSchemaProperty(fieldName, targetType, required, possibleValues);
 	}
 
@@ -161,14 +272,20 @@ class MappingMongoJsonSchemaCreator implements MongoJsonSchemaCreator {
 	JsonSchemaProperty createSchemaProperty(String fieldName, Object type, boolean required,
 			Collection<?> possibleValues) {
 
+		TypedJsonSchemaObject schemaObject = createSchemaObject(type, possibleValues);
+
+		return createPotentiallyRequiredSchemaProperty(JsonSchemaProperty.named(fieldName).with(schemaObject), required);
+	}
+
+	private TypedJsonSchemaObject createSchemaObject(Object type, Collection<?> possibleValues) {
+
 		TypedJsonSchemaObject schemaObject = type instanceof Type ? JsonSchemaObject.of(Type.class.cast(type))
 				: JsonSchemaObject.of(Class.class.cast(type));
 
 		if (!CollectionUtils.isEmpty(possibleValues)) {
 			schemaObject = schemaObject.possibleValues(possibleValues);
 		}
-
-		return createPotentiallyRequiredSchemaProperty(JsonSchemaProperty.named(fieldName).with(schemaObject), required);
+		return schemaObject;
 	}
 
 	private String computePropertyFieldName(PersistentProperty property) {
@@ -199,12 +316,53 @@ class MappingMongoJsonSchemaCreator implements MongoJsonSchemaCreator {
 		return mongoProperty.getFieldType() != mongoProperty.getActualType() ? Object.class : mongoProperty.getFieldType();
 	}
 
-	static JsonSchemaProperty createPotentiallyRequiredSchemaProperty(JsonSchemaProperty property, boolean required) {
+	private static Class<?> computeTargetType(Class<?> fallback, List<Object> possibleValues) {
+		return possibleValues.isEmpty() ? fallback : possibleValues.iterator().next().getClass();
+	}
 
-		if (!required) {
+	private <E extends Enum<E>> List<Object> getPossibleEnumValues(Class<E> targetType) {
+
+		EnumSet<E> enumSet = EnumSet.allOf(targetType);
+		List<Object> possibleValues = new ArrayList<>(enumSet.size());
+
+		for (Object enumValue : enumSet) {
+			possibleValues.add(converter.convertToMongoType(enumValue));
+		}
+
+		return possibleValues;
+	}
+
+	private static boolean isCollection(MongoPersistentProperty property) {
+		return property.isCollectionLike() && !property.getType().equals(byte[].class);
+	}
+
+	static JsonSchemaProperty createPotentiallyRequiredSchemaProperty(JsonSchemaProperty property, boolean required) {
+		return required ? JsonSchemaProperty.required(property) : property;
+	}
+
+	class PropertyContext implements JsonSchemaPropertyContext {
+
+		private final String path;
+		private final MongoPersistentProperty property;
+
+		public PropertyContext(String path, MongoPersistentProperty property) {
+			this.path = path;
+			this.property = property;
+		}
+
+		@Override
+		public String getPath() {
+			return path;
+		}
+
+		@Override
+		public MongoPersistentProperty getProperty() {
 			return property;
 		}
 
-		return JsonSchemaProperty.required(property);
+		@Override
+		public <T> MongoPersistentEntity<T> resolveEntity(MongoPersistentProperty property) {
+			return (MongoPersistentEntity<T>) mappingContext.getPersistentEntity(property);
+		}
 	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoClientSettingsFactoryBean.java

@@ -36,6 +36,7 @@ import com.mongodb.MongoClientSettings.Builder;
 import com.mongodb.ReadConcern;
 import com.mongodb.ReadPreference;
 import com.mongodb.ServerAddress;
+import com.mongodb.ServerApi;
 import com.mongodb.WriteConcern;
 import com.mongodb.connection.ClusterConnectionMode;
 import com.mongodb.connection.ClusterType;
@@ -113,6 +114,7 @@ public class MongoClientSettingsFactoryBean extends AbstractFactoryBean<MongoCli
 	// encryption and retry
 
 	private @Nullable AutoEncryptionSettings autoEncryptionSettings;
+	private @Nullable ServerApi serverApi;
 
 	/**
 	 * @param socketConnectTimeoutMS in msec
@@ -395,6 +397,15 @@ public class MongoClientSettingsFactoryBean extends AbstractFactoryBean<MongoCli
 		this.autoEncryptionSettings = autoEncryptionSettings;
 	}
 
+	/**
+	 * @param serverApi can be {@literal null}.
+	 * @see MongoClientSettings.Builder#serverApi(ServerApi)
+	 * @since 3.3
+	 */
+	public void setServerApi(@Nullable ServerApi serverApi) {
+		this.serverApi = serverApi;
+	}
+
 	@Override
 	public Class<?> getObjectType() {
 		return MongoClientSettings.class;
@@ -476,9 +487,11 @@ public class MongoClientSettingsFactoryBean extends AbstractFactoryBean<MongoCli
 		if (retryWrites != null) {
 			builder = builder.retryWrites(retryWrites);
 		}
-
 		if (uUidRepresentation != null) {
-			builder.uuidRepresentation(uUidRepresentation);
+			builder = builder.uuidRepresentation(uUidRepresentation);
+		}
+		if (serverApi != null) {
+			builder = builder.serverApi(serverApi);
 		}
 
 		return builder.build();

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoDatabaseFactorySupport.java

@@ -33,7 +33,7 @@ import com.mongodb.client.MongoDatabase;
 /**
  * Common base class for usage with both {@link com.mongodb.client.MongoClients} defining common properties such as
  * database name and exception translator.
- * <p/>
+ * <br />
  * Not intended to be used directly.
  *
  * @author Christoph Strobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoDbFactorySupport.java

@@ -20,7 +20,7 @@ import org.springframework.dao.support.PersistenceExceptionTranslator;
 /**
  * Common base class for usage with both {@link com.mongodb.client.MongoClients} defining common properties such as
  * database name and exception translator.
- * <p/>
+ * <br />
  * Not intended to be used directly.
  *
  * @author Christoph Strobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoExceptionTranslator.java

@@ -21,6 +21,7 @@ import java.util.HashSet;
 import java.util.Set;
 
 import org.bson.BsonInvalidOperationException;
+
 import org.springframework.dao.DataAccessException;
 import org.springframework.dao.DataAccessResourceFailureException;
 import org.springframework.dao.DataIntegrityViolationException;
@@ -39,6 +40,7 @@ import org.springframework.util.ClassUtils;
 import com.mongodb.MongoBulkWriteException;
 import com.mongodb.MongoException;
 import com.mongodb.MongoServerException;
+import com.mongodb.MongoSocketException;
 import com.mongodb.bulk.BulkWriteError;
 
 /**
@@ -49,6 +51,7 @@ import com.mongodb.bulk.BulkWriteError;
  * @author Oliver Gierke
  * @author Michal Vich
  * @author Christoph Strobl
+ * @author Brice Vandeputte
  */
 public class MongoExceptionTranslator implements PersistenceExceptionTranslator {
 
@@ -78,6 +81,10 @@ public class MongoExceptionTranslator implements PersistenceExceptionTranslator
 			throw new InvalidDataAccessApiUsageException(ex.getMessage(), ex);
 		}
 
+		if (ex instanceof MongoSocketException) {
+			return new DataAccessResourceFailureException(ex.getMessage(), ex);
+		}
+
 		String exception = ClassUtils.getShortName(ClassUtils.getUserClass(ex.getClass()));
 
 		if (DUPLICATE_KEY_EXCEPTIONS.contains(exception)) {

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoJsonSchemaCreator.java

@@ -15,7 +15,23 @@
  */
 package org.springframework.data.mongodb.core;
 
+import java.util.HashSet;
+import java.util.Set;
+import java.util.function.Predicate;
+
+import org.springframework.data.mapping.PersistentProperty;
+import org.springframework.data.mapping.context.MappingContext;
+import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
 import org.springframework.data.mongodb.core.convert.MongoConverter;
+import org.springframework.data.mongodb.core.convert.MongoCustomConversions;
+import org.springframework.data.mongodb.core.convert.NoOpDbRefResolver;
+import org.springframework.data.mongodb.core.mapping.Encrypted;
+import org.springframework.data.mongodb.core.mapping.MongoMappingContext;
+import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
+import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
+import org.springframework.data.mongodb.core.mapping.MongoSimpleTypes;
+import org.springframework.data.mongodb.core.mapping.Unwrapped.Nullable;
+import org.springframework.data.mongodb.core.schema.JsonSchemaProperty;
 import org.springframework.data.mongodb.core.schema.MongoJsonSchema;
 import org.springframework.util.Assert;
 
@@ -24,6 +40,7 @@ import org.springframework.util.Assert;
  * following mapping rules.
  * <p>
  * <strong>Required Properties</strong>
+ * </p>
  * <ul>
  * <li>Properties of primitive type</li>
  * </ul>
@@ -45,7 +62,8 @@ import org.springframework.util.Assert;
  * {@link org.springframework.data.annotation.Id _id} properties using types that can be converted into
  * {@link org.bson.types.ObjectId} like {@link String} will be mapped to {@code type : 'object'} unless there is more
  * specific information available via the {@link org.springframework.data.mongodb.core.mapping.MongoId} annotation.
- * </p>
+
+ * {@link Encrypted} properties will contain {@literal encrypt} information.
  *
  * @author Christoph Strobl
  * @since 2.2
@@ -60,6 +78,88 @@ public interface MongoJsonSchemaCreator {
 	 */
 	MongoJsonSchema createSchemaFor(Class<?> type);
 
+	/**
+	 * Filter matching {@link JsonSchemaProperty properties}.
+	 *
+	 * @param filter the {@link Predicate} to evaluate for inclusion. Must not be {@literal null}.
+	 * @return new instance of {@link MongoJsonSchemaCreator}.
+	 * @since 3.3
+	 */
+	MongoJsonSchemaCreator filter(Predicate<JsonSchemaPropertyContext> filter);
+
+	/**
+	 * The context in which a specific {@link #getProperty()} is encountered during schema creation.
+	 * 
+	 * @since 3.3
+	 */
+	interface JsonSchemaPropertyContext {
+
+		/**
+		 * The path to a given field/property in dot notation.
+		 * 
+		 * @return never {@literal null}.
+		 */
+		String getPath();
+
+		/**
+		 * The current property.
+		 * 
+		 * @return never {@literal null}.
+		 */
+		MongoPersistentProperty getProperty();
+
+		/**
+		 * Obtain the {@link MongoPersistentEntity} for a given property.
+		 * 
+		 * @param property must not be {@literal null}.
+		 * @param <T>
+		 * @return {@literal null} if the property is not an entity. It is nevertheless recommend to check
+		 *         {@link PersistentProperty#isEntity()} first.
+		 */
+		@Nullable
+		<T> MongoPersistentEntity<T> resolveEntity(MongoPersistentProperty property);
+
+	}
+
+	/**
+	 * A filter {@link Predicate} that matches {@link Encrypted encrypted properties} and those having nested ones.
+	 *
+	 * @return new instance of {@link Predicate}.
+	 * @since 3.3
+	 */
+	static Predicate<JsonSchemaPropertyContext> encryptedOnly() {
+
+		return new Predicate<JsonSchemaPropertyContext>() {
+
+			// cycle guard
+			private final Set<MongoPersistentProperty> seen = new HashSet<>();
+
+			@Override
+			public boolean test(JsonSchemaPropertyContext context) {
+				return extracted(context.getProperty(), context);
+			}
+
+			private boolean extracted(MongoPersistentProperty property, JsonSchemaPropertyContext context) {
+				if (property.isAnnotationPresent(Encrypted.class)) {
+					return true;
+				}
+
+				if (!property.isEntity() || seen.contains(property)) {
+					return false;
+				}
+
+				seen.add(property);
+
+				for (MongoPersistentProperty nested : context.resolveEntity(property)) {
+					if (extracted(nested, context)) {
+						return true;
+					}
+				}
+				return false;
+			}
+		};
+	}
+
 	/**
 	 * Creates a new {@link MongoJsonSchemaCreator} that is aware of conversions applied by the given
 	 * {@link MongoConverter}.
@@ -72,4 +172,41 @@ public interface MongoJsonSchemaCreator {
 		Assert.notNull(mongoConverter, "MongoConverter must not be null!");
 		return new MappingMongoJsonSchemaCreator(mongoConverter);
 	}
+
+	/**
+	 * Creates a new {@link MongoJsonSchemaCreator} that is aware of type mappings and potential
+	 * {@link org.springframework.data.spel.spi.EvaluationContextExtension extensions}.
+	 *
+	 * @param mappingContext must not be {@literal null}.
+	 * @return new instance of {@link MongoJsonSchemaCreator}.
+	 * @since 3.3
+	 */
+	static MongoJsonSchemaCreator create(MappingContext mappingContext) {
+
+		MappingMongoConverter converter = new MappingMongoConverter(NoOpDbRefResolver.INSTANCE, mappingContext);
+		converter.setCustomConversions(MongoCustomConversions.create(config -> {}));
+		converter.afterPropertiesSet();
+
+		return create(converter);
+	}
+
+	/**
+	 * Creates a new {@link MongoJsonSchemaCreator} that does not consider potential extensions - suitable for testing. We
+	 * recommend to use {@link #create(MappingContext)}.
+	 *
+	 * @return new instance of {@link MongoJsonSchemaCreator}.
+	 * @since 3.3
+	 */
+	static MongoJsonSchemaCreator create() {
+
+		MongoMappingContext mappingContext = new MongoMappingContext();
+		mappingContext.setSimpleTypeHolder(MongoSimpleTypes.HOLDER);
+		mappingContext.afterPropertiesSet();
+
+		MappingMongoConverter converter = new MappingMongoConverter(NoOpDbRefResolver.INSTANCE, mappingContext);
+		converter.setCustomConversions(MongoCustomConversions.create(config -> {}));
+		converter.afterPropertiesSet();
+
+		return create(converter);
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoOperations.java

@@ -58,7 +58,7 @@ import com.mongodb.client.result.UpdateResult;
  * Interface that specifies a basic set of MongoDB operations. Implemented by {@link MongoTemplate}. Not often used but
  * a useful option for extensibility and testability (as it can be easily mocked, stubbed, or be the target of a JDK
  * proxy).
- * <p/>
+ * <br />
  * <strong>NOTE:</strong> Some operations cannot be executed within a MongoDB transaction. Please refer to the MongoDB
  * specific documentation to learn more about <a href="https://docs.mongodb.com/manual/core/transactions/">Multi
  * Document Transactions</a>.
@@ -125,7 +125,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Executes a {@link DbCallback} translating any exceptions as necessary.
-	 * <p/>
+	 * <br />
 	 * Allows for returning a result object, that is a domain object or a collection of domain objects.
 	 *
 	 * @param action callback object that specifies the MongoDB actions to perform on the passed in DB instance. Must not
@@ -138,7 +138,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Executes the given {@link CollectionCallback} on the entity collection of the specified class.
-	 * <p/>
+	 * <br />
 	 * Allows for returning a result object, that is a domain object or a collection of domain objects.
 	 *
 	 * @param entityClass class that determines the collection to use. Must not be {@literal null}.
@@ -151,7 +151,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Executes the given {@link CollectionCallback} on the collection of the given name.
-	 * <p/>
+	 * <br />
 	 * Allows for returning a result object, that is a domain object or a collection of domain objects.
 	 *
 	 * @param collectionName the name of the collection that specifies which {@link MongoCollection} instance will be
@@ -176,7 +176,7 @@ public interface MongoOperations extends FluentMongoOperations {
 	/**
 	 * Obtain a {@link ClientSession session} bound instance of {@link SessionScoped} binding the {@link ClientSession}
 	 * provided by the given {@link Supplier} to each and every command issued against MongoDB.
-	 * <p/>
+	 * <br />
 	 * <strong>Note:</strong> It is up to the caller to manage the {@link ClientSession} lifecycle. Use the
 	 * {@link SessionScoped#execute(SessionCallback, Consumer)} hook to potentially close the {@link ClientSession}.
 	 *
@@ -212,7 +212,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Obtain a {@link ClientSession} bound instance of {@link MongoOperations}.
-	 * <p/>
+	 * <br />
 	 * <strong>Note:</strong> It is up to the caller to manage the {@link ClientSession} lifecycle.
 	 *
 	 * @param session must not be {@literal null}.
@@ -300,7 +300,7 @@ public interface MongoOperations extends FluentMongoOperations {
 	 * is created on first interaction with the server. Collections can be explicitly created via
 	 * {@link #createCollection(Class)}. Please make sure to check if the collection {@link #collectionExists(Class)
 	 * exists} first.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param collectionName name of the collection. Must not be {@literal null}.
@@ -310,7 +310,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Check to see if a collection with a name indicated by the entity class exists.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param entityClass class that determines the name of the collection. Must not be {@literal null}.
@@ -320,7 +320,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Check to see if a collection with a given name exists.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param collectionName name of the collection. Must not be {@literal null}.
@@ -330,7 +330,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Drop the collection with the name indicated by the entity class.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param entityClass class that determines the collection to drop/delete. Must not be {@literal null}.
@@ -339,7 +339,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Drop the collection with the given name.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param collectionName name of the collection to drop/delete.
@@ -403,10 +403,10 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Query for a list of objects of type T from the collection used by the entity class.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your collection does not contain a homogeneous collection of types, this operation will not be an efficient way
 	 * to map objects since the test for class type is done in the client and not on the server.
 	 *
@@ -417,10 +417,10 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Query for a list of objects of type T from the specified collection.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your collection does not contain a homogeneous collection of types, this operation will not be an efficient way
 	 * to map objects since the test for class type is done in the client and not on the server.
 	 *
@@ -539,11 +539,11 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Execute an aggregation operation backed by a Mongo DB {@link com.mongodb.client.AggregateIterable}.
-	 * <p/>
+	 * <br />
 	 * Returns a {@link CloseableIterator} that wraps the a Mongo DB {@link com.mongodb.client.AggregateIterable} that
 	 * needs to be closed. The raw results will be mapped to the given entity class and are returned as stream. The name
 	 * of the inputCollection is derived from the inputType of the aggregation.
-	 * <p/>
+	 * <br />
 	 * Aggregation streaming can't be used with {@link AggregationOptions#isExplain() aggregation explain}. Enabling
 	 * explanation mode will throw an {@link IllegalArgumentException}.
 	 *
@@ -557,10 +557,10 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Execute an aggregation operation backed by a Mongo DB {@link com.mongodb.client.AggregateIterable}.
-	 * <p/>
+	 * <br />
 	 * Returns a {@link CloseableIterator} that wraps the a Mongo DB {@link com.mongodb.client.AggregateIterable} that
 	 * needs to be closed. The raw results will be mapped to the given entity class.
-	 * <p/>
+	 * <br />
 	 * Aggregation streaming can't be used with {@link AggregationOptions#isExplain() aggregation explain}. Enabling
 	 * explanation mode will throw an {@link IllegalArgumentException}.
 	 *
@@ -576,10 +576,10 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Execute an aggregation operation backed by a Mongo DB {@link com.mongodb.client.AggregateIterable}.
-	 * <p/>
+	 * <br />
 	 * Returns a {@link CloseableIterator} that wraps the a Mongo DB {@link com.mongodb.client.AggregateIterable} that
 	 * needs to be closed. The raw results will be mapped to the given entity class.
-	 * <p/>
+	 * <br />
 	 * Aggregation streaming can't be used with {@link AggregationOptions#isExplain() aggregation explain}. Enabling
 	 * explanation mode will throw an {@link IllegalArgumentException}.
 	 *
@@ -702,10 +702,10 @@ public interface MongoOperations extends FluentMongoOperations {
 	/**
 	 * Map the results of an ad-hoc query on the collection for the entity class to a single instance of an object of the
 	 * specified type.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -720,10 +720,10 @@ public interface MongoOperations extends FluentMongoOperations {
 	/**
 	 * Map the results of an ad-hoc query on the specified collection to a single instance of an object of the specified
 	 * type.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -768,10 +768,10 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Map the results of an ad-hoc query on the collection for the entity class to a List of the specified type.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -784,10 +784,10 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Map the results of an ad-hoc query on the specified collection to a List of the specified type.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -881,7 +881,7 @@ public interface MongoOperations extends FluentMongoOperations {
 	}
 
 	/**
-	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify <a/>
+	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify </a>
 	 * to apply provided {@link Update} on documents matching {@link Criteria} of given {@link Query}.
 	 *
 	 * @param query the {@link Query} class that specifies the {@link Criteria} used to find a record and also an optional
@@ -897,7 +897,7 @@ public interface MongoOperations extends FluentMongoOperations {
 	<T> T findAndModify(Query query, UpdateDefinition update, Class<T> entityClass);
 
 	/**
-	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify <a/>
+	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify </a>
 	 * to apply provided {@link Update} on documents matching {@link Criteria} of given {@link Query}.
 	 *
 	 * @param query the {@link Query} class that specifies the {@link Criteria} used to find a record and also an optional
@@ -914,7 +914,7 @@ public interface MongoOperations extends FluentMongoOperations {
 	<T> T findAndModify(Query query, UpdateDefinition update, Class<T> entityClass, String collectionName);
 
 	/**
-	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify <a/>
+	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify </a>
 	 * to apply provided {@link Update} on documents matching {@link Criteria} of given {@link Query} taking
 	 * {@link FindAndModifyOptions} into account.
 	 *
@@ -934,7 +934,7 @@ public interface MongoOperations extends FluentMongoOperations {
 	<T> T findAndModify(Query query, UpdateDefinition update, FindAndModifyOptions options, Class<T> entityClass);
 
 	/**
-	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify <a/>
+	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify </a>
 	 * to apply provided {@link Update} on documents matching {@link Criteria} of given {@link Query} taking
 	 * {@link FindAndModifyOptions} into account.
 	 *
@@ -957,7 +957,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement}
 	 * document. <br />
 	 * The collection name is derived from the {@literal replacement} type. <br />
@@ -977,7 +977,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement}
 	 * document.<br />
 	 * Options are defaulted to {@link FindAndReplaceOptions#empty()}. <br />
@@ -997,7 +997,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account.<br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -1018,7 +1018,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account.<br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -1041,7 +1041,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account.<br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -1066,7 +1066,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account.<br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -1094,7 +1094,7 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account.<br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -1120,9 +1120,9 @@ public interface MongoOperations extends FluentMongoOperations {
 	 * Map the results of an ad-hoc query on the collection for the entity type to a single instance of an object of the
 	 * specified type. The first document that matches the query is returned and also removed from the collection in the
 	 * database.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -1137,10 +1137,10 @@ public interface MongoOperations extends FluentMongoOperations {
 	/**
 	 * Map the results of an ad-hoc query on the specified collection to a single instance of an object of the specified
 	 * type. The first document that matches the query is returned and also removed from the collection in the database.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -1160,6 +1160,12 @@ public interface MongoOperations extends FluentMongoOperations {
 	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
 	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
 	 * count all matches.
+	 * <br />
+	 * This method uses an
+	 * {@link com.mongodb.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} even for empty {@link Query queries} which may have an impact on performance, but guarantees
+	 * shard, session and transaction compliance. In case an inaccurate count satisfies the applications needs use
+	 * {@link #estimatedCount(Class)} for empty queries instead.
 	 *
 	 * @param query the {@link Query} class that specifies the criteria used to find documents. Must not be
 	 *          {@literal null}.
@@ -1176,6 +1182,12 @@ public interface MongoOperations extends FluentMongoOperations {
 	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
 	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
 	 * count all matches.
+	 * <br />
+	 * This method uses an
+	 * {@link com.mongodb.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} even for empty {@link Query queries} which may have an impact on performance, but guarantees
+	 * shard, session and transaction compliance. In case an inaccurate count satisfies the applications needs use
+	 * {@link #estimatedCount(String)} for empty queries instead.
 	 *
 	 * @param query the {@link Query} class that specifies the criteria used to find documents.
 	 * @param collectionName must not be {@literal null} or empty.
@@ -1187,6 +1199,9 @@ public interface MongoOperations extends FluentMongoOperations {
 	/**
 	 * Estimate the number of documents, in the collection {@link #getCollectionName(Class) identified by the given type},
 	 * based on collection statistics.
+	 * <br />
+	 * Please make sure to read the MongoDB reference documentation about limitations on eg. sharded cluster or inside
+	 * transactions.
 	 *
 	 * @param entityClass must not be {@literal null}.
 	 * @return the estimated number of documents.
@@ -1200,6 +1215,9 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Estimate the number of documents in the given collection based on collection statistics.
+	 * <br />
+	 * Please make sure to read the MongoDB reference documentation about limitations on eg. sharded cluster or inside
+	 * transactions.
 	 *
 	 * @param collectionName must not be {@literal null}.
 	 * @return the estimated number of documents.
@@ -1214,6 +1232,12 @@ public interface MongoOperations extends FluentMongoOperations {
 	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
 	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
 	 * count all matches.
+	 * <br />
+	 * This method uses an
+	 * {@link com.mongodb.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} even for empty {@link Query queries} which may have an impact on performance, but guarantees
+	 * shard, session and transaction compliance. In case an inaccurate count satisfies the applications needs use
+	 * {@link #estimatedCount(String)} for empty queries instead.
 	 *
 	 * @param query the {@link Query} class that specifies the criteria used to find documents. Must not be
 	 *          {@literal null}.
@@ -1225,34 +1249,39 @@ public interface MongoOperations extends FluentMongoOperations {
 
 	/**
 	 * Insert the object into the collection for the entity type of the object to save.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}.
-	 * <p/>
+	 * <br />
 	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
 	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
 	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
 	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
 	 * Type Conversion"</a> for more details.
-	 * <p/>
-	 * <p/>
+	 * <br />
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.
+	 * <br />
+	 * The {@code objectToSave} must not be collection-like.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
 	 * @return the inserted object.
+	 * @throws IllegalArgumentException in case the {@code objectToSave} is collection-like.
 	 */
 	<T> T insert(T objectToSave);
 
 	/**
 	 * Insert the object into the specified collection.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.
+	 * <br />
+	 * The {@code objectToSave} must not be collection-like.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
 	 * @param collectionName name of the collection to store the object in. Must not be {@literal null}.
 	 * @return the inserted object.
+	 * @throws IllegalArgumentException in case the {@code objectToSave} is collection-like.
 	 */
 	<T> T insert(T objectToSave, String collectionName);
 
@@ -1286,37 +1315,42 @@ public interface MongoOperations extends FluentMongoOperations {
 	/**
 	 * Save the object to the collection for the entity type of the object to save. This will perform an insert if the
 	 * object is not already present, that is an 'upsert'.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
 	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
 	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
 	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
 	 * Type Conversion"</a> for more details.
+	 * <br />
+	 * The {@code objectToSave} must not be collection-like.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
 	 * @return the saved object.
+	 * @throws IllegalArgumentException in case the {@code objectToSave} is collection-like.
 	 */
 	<T> T save(T objectToSave);
 
 	/**
 	 * Save the object to the specified collection. This will perform an insert if the object is not already present, that
 	 * is an 'upsert'.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
 	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
-	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See <a
-	 * https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation">Spring's Type
-	 * Conversion"</a> for more details.
+	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API.
+	 * See <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation">Spring's Type Conversion</a> for more details.
+	 * <br />
+	 * The {@code objectToSave} must not be collection-like.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
 	 * @param collectionName name of the collection to store the object in. Must not be {@literal null}.
 	 * @return the saved object.
+	 * @throws IllegalArgumentException in case the {@code objectToSave} is collection-like.
 	 */
 	<T> T save(T objectToSave, String collectionName);
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoServerApiFactoryBean.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.core;
+
+import org.springframework.beans.factory.FactoryBean;
+import org.springframework.lang.Nullable;
+import org.springframework.util.ObjectUtils;
+
+import com.mongodb.ServerApi;
+import com.mongodb.ServerApi.Builder;
+import com.mongodb.ServerApiVersion;
+
+/**
+ * {@link FactoryBean} for creating {@link ServerApi} using the {@link ServerApi.Builder}.
+ *
+ * @author Christoph Strobl
+ * @since 3.3
+ */
+public class MongoServerApiFactoryBean implements FactoryBean<ServerApi> {
+
+	private String version;
+	private @Nullable Boolean deprecationErrors;
+	private @Nullable Boolean strict;
+
+	/**
+	 * @param version the version string either as the enum name or the server version value.
+	 * @see ServerApiVersion
+	 */
+	public void setVersion(String version) {
+		this.version = version;
+	}
+
+	/**
+	 * @param deprecationErrors
+	 * @see ServerApi.Builder#deprecationErrors(boolean)
+	 */
+	public void setDeprecationErrors(@Nullable Boolean deprecationErrors) {
+		this.deprecationErrors = deprecationErrors;
+	}
+
+	/**
+	 * @param strict
+	 * @see ServerApi.Builder#strict(boolean)
+	 */
+	public void setStrict(@Nullable Boolean strict) {
+		this.strict = strict;
+	}
+
+	@Nullable
+	@Override
+	public ServerApi getObject() throws Exception {
+
+		Builder builder = ServerApi.builder().version(version());
+
+		if (deprecationErrors != null) {
+			builder = builder.deprecationErrors(deprecationErrors);
+		}
+		if (strict != null) {
+			builder = builder.strict(strict);
+		}
+		return builder.build();
+	}
+
+	@Nullable
+	@Override
+	public Class<?> getObjectType() {
+		return ServerApi.class;
+	}
+
+	private ServerApiVersion version() {
+		try {
+			// lookup by name eg. 'V1'
+			return ObjectUtils.caseInsensitiveValueOf(ServerApiVersion.values(), version);
+		} catch (IllegalArgumentException e) {
+			// or just the version number, eg. just '1'
+			return ServerApiVersion.findByValue(version);
+		}
+	}
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MongoTemplate.java

@@ -47,6 +47,7 @@ import org.springframework.data.geo.Distance;
 import org.springframework.data.geo.GeoResult;
 import org.springframework.data.geo.GeoResults;
 import org.springframework.data.geo.Metric;
+import org.springframework.data.mapping.MappingException;
 import org.springframework.data.mapping.callback.EntityCallbacks;
 import org.springframework.data.mapping.context.MappingContext;
 import org.springframework.data.mongodb.MongoDatabaseFactory;
@@ -55,6 +56,7 @@ import org.springframework.data.mongodb.SessionSynchronization;
 import org.springframework.data.mongodb.core.BulkOperations.BulkMode;
 import org.springframework.data.mongodb.core.DefaultBulkOperations.BulkOperationContext;
 import org.springframework.data.mongodb.core.EntityOperations.AdaptibleEntity;
+import org.springframework.data.mongodb.core.QueryOperations.AggregationDefinition;
 import org.springframework.data.mongodb.core.QueryOperations.CountContext;
 import org.springframework.data.mongodb.core.QueryOperations.DeleteContext;
 import org.springframework.data.mongodb.core.QueryOperations.DistinctQueryContext;
@@ -97,12 +99,12 @@ import org.springframework.data.mongodb.core.query.NearQuery;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.core.query.UpdateDefinition;
 import org.springframework.data.mongodb.core.query.UpdateDefinition.ArrayFilter;
+import org.springframework.data.mongodb.core.timeseries.Granularity;
 import org.springframework.data.mongodb.core.validation.Validator;
 import org.springframework.data.mongodb.util.BsonUtils;
 import org.springframework.data.projection.SpelAwareProxyProjectionFactory;
 import org.springframework.data.util.CloseableIterator;
 import org.springframework.data.util.Optionals;
-import org.springframework.jca.cci.core.ConnectionCallback;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -157,22 +159,12 @@ import com.mongodb.client.result.UpdateResult;
  * @author Roman Puchkovskiy
  * @author Yadhukrishna S Pai
  * @author Anton Barkan
+ * @author Bartłomiej Mazur
  */
 public class MongoTemplate implements MongoOperations, ApplicationContextAware, IndexOperationsProvider {
 
 	private static final Logger LOGGER = LoggerFactory.getLogger(MongoTemplate.class);
 	private static final WriteResultChecking DEFAULT_WRITE_RESULT_CHECKING = WriteResultChecking.NONE;
-	private static final Collection<String> ITERABLE_CLASSES;
-
-	static {
-
-		Set<String> iterableClasses = new HashSet<>();
-		iterableClasses.add(List.class.getName());
-		iterableClasses.add(Collection.class.getName());
-		iterableClasses.add(Iterator.class.getName());
-
-		ITERABLE_CLASSES = Collections.unmodifiableCollection(iterableClasses);
-	}
 
 	private final MongoConverter mongoConverter;
 	private final MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext;
@@ -346,7 +338,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	/**
 	 * Set the {@link EntityCallbacks} instance to use when invoking
 	 * {@link org.springframework.data.mapping.callback.EntityCallback callbacks} like the {@link BeforeSaveCallback}.
-	 * <p />
+	 * <br />
 	 * Overrides potentially existing {@link EntityCallbacks}.
 	 *
 	 * @param entityCallbacks must not be {@literal null}.
@@ -606,7 +598,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @see org.springframework.data.mongodb.core.MongoOperations#createCollection(java.lang.Class)
 	 */
 	public <T> MongoCollection<Document> createCollection(Class<T> entityClass) {
-		return createCollection(entityClass, CollectionOptions.empty());
+		return createCollection(entityClass, operations.forType(entityClass).getCollectionOptions());
 	}
 
 	/*
@@ -715,12 +707,17 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		});
 	}
 
+	@Override
+	public IndexOperations indexOps(String collectionName) {
+		return indexOps(collectionName, null);
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.ExecutableInsertOperation#indexOps(java.lang.String)
 	 */
-	public IndexOperations indexOps(String collectionName) {
-		return new DefaultIndexOperations(this, collectionName, null);
+	public IndexOperations indexOps(String collectionName, @Nullable Class<?> type) {
+		return new DefaultIndexOperations(this, collectionName, type);
 	}
 
 	/*
@@ -728,7 +725,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @see org.springframework.data.mongodb.core.ExecutableInsertOperation#indexOps(java.lang.Class)
 	 */
 	public IndexOperations indexOps(Class<?> entityClass) {
-		return new DefaultIndexOperations(this, getCollectionName(entityClass), entityClass);
+		return indexOps(getCollectionName(entityClass), entityClass);
 	}
 
 	/*
@@ -977,7 +974,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		for (Document element : results) {
 
 			GeoResult<T> geoResult = callback.doWith(element);
-			aggregate = aggregate.add(new BigDecimal(geoResult.getDistance().getValue()));
+			aggregate = aggregate.add(BigDecimal.valueOf(geoResult.getDistance().getValue()));
 			result.add(geoResult);
 		}
 
@@ -1177,11 +1174,28 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		return (T) doInsert(collectionName, objectToSave, this.mongoConverter);
 	}
 
-	protected void ensureNotIterable(@Nullable Object o) {
-		if (o != null) {
-			if (o.getClass().isArray() || ITERABLE_CLASSES.contains(o.getClass().getName())) {
-				throw new IllegalArgumentException("Cannot use a collection here.");
-			}
+	/**
+	 * Ensure the given {@literal source} is not an {@link java.lang.reflect.Array}, {@link Collection} or
+	 * {@link Iterator}.
+	 *
+	 * @param source can be {@literal null}.
+	 * @deprecated since 3.2. Call {@link #ensureNotCollectionLike(Object)} instead.
+	 */
+	protected void ensureNotIterable(@Nullable Object source) {
+		ensureNotCollectionLike(source);
+	}
+
+	/**
+	 * Ensure the given {@literal source} is not an {@link java.lang.reflect.Array}, {@link Collection} or
+	 * {@link Iterator}.
+	 *
+	 * @param source can be {@literal null}.
+	 * @since 3.2.
+	 */
+	protected void ensureNotCollectionLike(@Nullable Object source) {
+
+		if (EntityOperations.isCollectionLike(source)) {
+			throw new IllegalArgumentException("Cannot use a collection here.");
 		}
 	}
 
@@ -1364,13 +1378,13 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 		Assert.notNull(objectToSave, "Object to save must not be null!");
 		Assert.hasText(collectionName, "Collection name must not be null or empty!");
+		ensureNotCollectionLike(objectToSave);
 
 		AdaptibleEntity<T> source = operations.forEntity(objectToSave, mongoConverter.getConversionService());
 
 		return source.isVersionedEntity() //
 				? doSaveVersioned(source, collectionName) //
 				: (T) doSave(collectionName, objectToSave, this.mongoConverter);
-
 	}
 
 	@SuppressWarnings("unchecked")
@@ -1988,7 +2002,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	public <O> AggregationResults<O> aggregate(Aggregation aggregation, Class<?> inputType, Class<O> outputType) {
 
 		return aggregate(aggregation, getCollectionName(inputType), outputType,
-				new TypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper));
+				queryOperations.createAggregation(aggregation, inputType).getAggregationOperationContext());
 	}
 
 	/* (non-Javadoc)
@@ -2095,9 +2109,13 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		Assert.notNull(aggregation, "Aggregation pipeline must not be null!");
 		Assert.notNull(outputType, "Output type must not be null!");
 
-		AggregationOperationContext contextToUse = new AggregationUtil(queryMapper, mappingContext)
-				.prepareAggregationContext(aggregation, context);
-		return doAggregate(aggregation, collectionName, outputType, contextToUse);
+		return doAggregate(aggregation, collectionName, outputType,
+				queryOperations.createAggregation(aggregation, context));
+	}
+
+	private <O> AggregationResults<O> doAggregate(Aggregation aggregation, String collectionName, Class<O> outputType,
+			AggregationDefinition context) {
+		return doAggregate(aggregation, collectionName, outputType, context.getAggregationOperationContext());
 	}
 
 	@SuppressWarnings("ConstantConditions")
@@ -2185,11 +2203,10 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		Assert.notNull(outputType, "Output type must not be null!");
 		Assert.isTrue(!aggregation.getOptions().isExplain(), "Can't use explain option with streaming!");
 
-		AggregationUtil aggregationUtil = new AggregationUtil(queryMapper, mappingContext);
-		AggregationOperationContext rootContext = aggregationUtil.prepareAggregationContext(aggregation, context);
+		AggregationDefinition aggregationDefinition = queryOperations.createAggregation(aggregation, context);
 
 		AggregationOptions options = aggregation.getOptions();
-		List<Document> pipeline = aggregationUtil.createPipeline(aggregation, rootContext);
+		List<Document> pipeline = aggregationDefinition.getAggregationPipeline();
 
 		if (LOGGER.isDebugEnabled()) {
 			LOGGER.debug("Streaming aggregation: {} in collection {}", serializeToJsonSafely(pipeline), collectionName);
@@ -2418,6 +2435,20 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 				co.validationOptions(options);
 			}
 
+			if (collectionOptions.containsKey("timeseries")) {
+
+				Document timeSeries = collectionOptions.get("timeseries", Document.class);
+				com.mongodb.client.model.TimeSeriesOptions options = new com.mongodb.client.model.TimeSeriesOptions(
+						timeSeries.getString("timeField"));
+				if (timeSeries.containsKey("metaField")) {
+					options.metaField(timeSeries.getString("metaField"));
+				}
+				if (timeSeries.containsKey("granularity")) {
+					options.granularity(TimeSeriesGranularity.valueOf(timeSeries.getString("granularity").toUpperCase()));
+				}
+				co.timeSeriesOptions(options);
+			}
+
 			db.createCollection(collectionName, co);
 
 			MongoCollection<Document> coll = db.getCollection(collectionName, Document.class);
@@ -2572,6 +2603,19 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 			collectionOptions.getValidationOptions().ifPresent(it -> it.getValidator() //
 					.ifPresent(val -> doc.put("validator", getMappedValidator(val, targetType))));
+
+			collectionOptions.getTimeSeriesOptions().map(operations.forType(targetType)::mapTimeSeriesOptions)
+					.ifPresent(it -> {
+
+						Document timeseries = new Document("timeField", it.getTimeField());
+						if (StringUtils.hasText(it.getMetaField())) {
+							timeseries.append("metaField", it.getMetaField());
+						}
+						if (!Granularity.DEFAULT.equals(it.getGranularity())) {
+							timeseries.append("granularity", it.getGranularity().name().toLowerCase());
+						}
+						doc.put("timeseries", timeseries);
+					});
 		}
 
 		return doc;
@@ -2619,7 +2663,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	/**
 	 * Map the results of an ad-hoc query on the default MongoDB collection to an object using the template's converter.
 	 * The first document that matches the query is returned and also removed from the collection in the database.
-	 * <p/>
+	 * <br />
 	 * The query document is specified as a standard Document and so is the fields specification.
 	 *
 	 * @param collectionName name of the collection to retrieve the objects from
@@ -2735,25 +2779,24 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * Internal method using callbacks to do queries against the datastore that requires reading a single object from a
 	 * collection of objects. It will take the following steps
 	 * <ol>
-	 * <li>Execute the given {@link ConnectionCallback} for a {@link Document}.</li>
+	 * <li>Execute the given {@link CollectionCallback} for a {@link Document}.</li>
 	 * <li>Apply the given {@link DocumentCallback} to each of the {@link Document}s to obtain the result.</li>
 	 * <ol>
 	 *
 	 * @param <T>
 	 * @param collectionCallback the callback to retrieve the {@link Document} with
-	 * @param objectCallback the {@link DocumentCallback} to transform {@link Document}s into the actual domain type
+	 * @param documentCallback the {@link DocumentCallback} to transform {@link Document}s into the actual domain type
 	 * @param collectionName the collection to be queried
 	 * @return
 	 */
 	@Nullable
 	private <T> T executeFindOneInternal(CollectionCallback<Document> collectionCallback,
-			DocumentCallback<T> objectCallback, String collectionName) {
+			DocumentCallback<T> documentCallback, String collectionName) {
 
 		try {
 
-			T result = objectCallback
-					.doWith(collectionCallback.doInCollection(getAndPrepareCollection(doGetDatabase(), collectionName)));
-			return result;
+			Document document = collectionCallback.doInCollection(getAndPrepareCollection(doGetDatabase(), collectionName));
+			return document != null ? documentCallback.doWith(document) : null;
 		} catch (RuntimeException e) {
 			throw potentiallyConvertRuntimeException(e, exceptionTranslator);
 		}
@@ -2763,7 +2806,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * Internal method using callback to do queries against the datastore that requires reading a collection of objects.
 	 * It will take the following steps
 	 * <ol>
-	 * <li>Execute the given {@link ConnectionCallback} for a {@link FindIterable}.</li>
+	 * <li>Execute the given {@link CollectionCallback} for a {@link FindIterable}.</li>
 	 * <li>Prepare that {@link FindIterable} with the given {@link CursorPreparer} (will be skipped if
 	 * {@link CursorPreparer} is {@literal null}</li>
 	 * <li>Iterate over the {@link FindIterable} and applies the given {@link DocumentCallback} to each of the
@@ -2773,36 +2816,27 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @param <T>
 	 * @param collectionCallback the callback to retrieve the {@link FindIterable} with
 	 * @param preparer the {@link CursorPreparer} to potentially modify the {@link FindIterable} before iterating over it
-	 * @param objectCallback the {@link DocumentCallback} to transform {@link Document}s into the actual domain type
+	 * @param documentCallback the {@link DocumentCallback} to transform {@link Document}s into the actual domain type
 	 * @param collectionName the collection to be queried
 	 * @return
 	 */
 	private <T> List<T> executeFindMultiInternal(CollectionCallback<FindIterable<Document>> collectionCallback,
-			CursorPreparer preparer, DocumentCallback<T> objectCallback, String collectionName) {
+			CursorPreparer preparer, DocumentCallback<T> documentCallback, String collectionName) {
 
 		try {
 
-			MongoCursor<Document> cursor = null;
-
-			try {
-
-				cursor = preparer
-						.initiateFind(getAndPrepareCollection(doGetDatabase(), collectionName), collectionCallback::doInCollection)
-						.iterator();
+			try (MongoCursor<Document> cursor = preparer
+					.initiateFind(getAndPrepareCollection(doGetDatabase(), collectionName), collectionCallback::doInCollection)
+					.iterator()) {
 
 				List<T> result = new ArrayList<>();
 
 				while (cursor.hasNext()) {
 					Document object = cursor.next();
-					result.add(objectCallback.doWith(object));
+					result.add(documentCallback.doWith(object));
 				}
 
 				return result;
-			} finally {
-
-				if (cursor != null) {
-					cursor.close();
-				}
 			}
 		} catch (RuntimeException e) {
 			throw potentiallyConvertRuntimeException(e, exceptionTranslator);
@@ -2812,23 +2846,12 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	private void executeQueryInternal(CollectionCallback<FindIterable<Document>> collectionCallback,
 			CursorPreparer preparer, DocumentCallbackHandler callbackHandler, String collectionName) {
 
-		try {
+		try (MongoCursor<Document> cursor = preparer
+				.initiateFind(getAndPrepareCollection(doGetDatabase(), collectionName), collectionCallback::doInCollection)
+				.iterator()) {
 
-			MongoCursor<Document> cursor = null;
-
-			try {
-
-				cursor = preparer
-						.initiateFind(getAndPrepareCollection(doGetDatabase(), collectionName), collectionCallback::doInCollection)
-						.iterator();
-
-				while (cursor.hasNext()) {
-					callbackHandler.processDocument(cursor.next());
-				}
-			} finally {
-				if (cursor != null) {
-					cursor.close();
-				}
+			while (cursor.hasNext()) {
+				callbackHandler.processDocument(cursor.next());
 			}
 		} catch (RuntimeException e) {
 			throw potentiallyConvertRuntimeException(e, exceptionTranslator);
@@ -3127,8 +3150,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 	interface DocumentCallback<T> {
 
-		@Nullable
-		T doWith(@Nullable Document object);
+		T doWith(Document object);
 	}
 
 	/**
@@ -3152,22 +3174,19 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 			this.collectionName = collectionName;
 		}
 
-		@Nullable
-		public T doWith(@Nullable Document document) {
+		public T doWith(Document document) {
 
-			T source = null;
+			maybeEmitEvent(new AfterLoadEvent<>(document, type, collectionName));
+			T entity = reader.read(type, document);
 
-			if (document != null) {
-				maybeEmitEvent(new AfterLoadEvent<>(document, type, collectionName));
-				source = reader.read(type, document);
+			if (entity == null) {
+				throw new MappingException(String.format("EntityReader %s returned null", reader));
 			}
 
-			if (source != null) {
-				maybeEmitEvent(new AfterConvertEvent<>(document, source, collectionName));
-				source = maybeCallAfterConvert(source, document, collectionName);
-			}
+			maybeEmitEvent(new AfterConvertEvent<>(document, entity, collectionName));
+			entity = maybeCallAfterConvert(entity, document, collectionName);
 
-			return source;
+			return entity;
 		}
 	}
 
@@ -3200,8 +3219,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		 * @see org.springframework.data.mongodb.core.MongoTemplate.DocumentCallback#doWith(org.bson.Document)
 		 */
 		@SuppressWarnings("unchecked")
-		@Nullable
-		public T doWith(@Nullable Document document) {
+		public T doWith(Document document) {
 
 			if (document == null) {
 				return null;
@@ -3212,15 +3230,16 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 			maybeEmitEvent(new AfterLoadEvent<>(document, targetType, collectionName));
 
-			Object source = reader.read(typeToRead, document);
-			Object result = targetType.isInterface() ? projectionFactory.createProjection(targetType, source) : source;
+			Object entity = reader.read(typeToRead, document);
 
-			if (result != null) {
-				maybeEmitEvent(new AfterConvertEvent<>(document, result, collectionName));
-				result = maybeCallAfterConvert(result, document, collectionName);
+			if (entity == null) {
+				throw new MappingException(String.format("EntityReader %s returned null", reader));
 			}
 
-			return (T) result;
+			Object result = targetType.isInterface() ? projectionFactory.createProjection(targetType, entity) : entity;
+
+			maybeEmitEvent(new AfterConvertEvent<>(document, result, collectionName));
+			return (T) maybeCallAfterConvert(result, document, collectionName);
 		}
 	}
 
@@ -3357,8 +3376,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 			this.metric = metric;
 		}
 
-		@Nullable
-		public GeoResult<T> doWith(@Nullable Document object) {
+		public GeoResult<T> doWith(Document object) {
 
 			double distance = Double.NaN;
 			if (object.containsKey(distanceField)) {
@@ -3385,10 +3403,6 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 		/**
 		 * Creates a new {@link CloseableIterableCursorAdapter} backed by the given {@link MongoCollection}.
-		 *
-		 * @param cursor
-		 * @param exceptionTranslator
-		 * @param objectReadCallback
 		 */
 		CloseableIterableCursorAdapter(MongoIterable<Document> cursor, PersistenceExceptionTranslator exceptionTranslator,
 				DocumentCallback<T> objectReadCallback) {
@@ -3432,8 +3446,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 			try {
 				Document item = cursor.next();
-				T converted = objectReadCallback.doWith(item);
-				return converted;
+				return objectReadCallback.doWith(item);
 			} catch (RuntimeException ex) {
 				throw potentiallyConvertRuntimeException(ex, exceptionTranslator);
 			}
@@ -3459,14 +3472,27 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		}
 	}
 
+	/**
+	 * @deprecated since 3.1.4. Use {@link #getMongoDatabaseFactory()} instead.
+	 * @return the {@link MongoDatabaseFactory} in use.
+	 */
+	@Deprecated
 	public MongoDatabaseFactory getMongoDbFactory() {
+		return getMongoDatabaseFactory();
+	}
+
+	/**
+	 * @return the {@link MongoDatabaseFactory} in use.
+	 * @since 3.1.4
+	 */
+	public MongoDatabaseFactory getMongoDatabaseFactory() {
 		return mongoDbFactory;
 	}
 
 	/**
 	 * {@link MongoTemplate} extension bound to a specific {@link ClientSession} that is applied when interacting with the
 	 * server through the driver API.
-	 * <p />
+	 * <br />
 	 * The prepare steps for {@link MongoDatabase} and {@link MongoCollection} proxy the target and invoke the desired
 	 * target method matching the actual arguments plus a {@link ClientSession}.
 	 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/QueryOperations.java

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.core;
 
 import java.util.List;
 import java.util.Map;
+import java.util.Map.Entry;
 import java.util.Optional;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
@@ -31,11 +32,17 @@ import org.springframework.data.mapping.PropertyPath;
 import org.springframework.data.mapping.PropertyReferenceException;
 import org.springframework.data.mapping.context.MappingContext;
 import org.springframework.data.mongodb.CodecRegistryProvider;
+import org.springframework.data.mongodb.MongoExpression;
 import org.springframework.data.mongodb.core.MappedDocument.MappedUpdate;
 import org.springframework.data.mongodb.core.aggregation.Aggregation;
+import org.springframework.data.mongodb.core.aggregation.AggregationExpression;
 import org.springframework.data.mongodb.core.aggregation.AggregationOperationContext;
+import org.springframework.data.mongodb.core.aggregation.AggregationOptions;
+import org.springframework.data.mongodb.core.aggregation.AggregationPipeline;
 import org.springframework.data.mongodb.core.aggregation.AggregationUpdate;
 import org.springframework.data.mongodb.core.aggregation.RelaxedTypeBasedAggregationOperationContext;
+import org.springframework.data.mongodb.core.aggregation.TypeBasedAggregationOperationContext;
+import org.springframework.data.mongodb.core.aggregation.TypedAggregation;
 import org.springframework.data.mongodb.core.convert.QueryMapper;
 import org.springframework.data.mongodb.core.convert.UpdateMapper;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
@@ -48,6 +55,7 @@ import org.springframework.data.mongodb.core.query.UpdateDefinition;
 import org.springframework.data.mongodb.core.query.UpdateDefinition.ArrayFilter;
 import org.springframework.data.mongodb.util.BsonUtils;
 import org.springframework.data.projection.ProjectionFactory;
+import org.springframework.data.util.Lazy;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
@@ -194,9 +202,34 @@ class QueryOperations {
 		return new DeleteContext(query, false);
 	}
 
+	/**
+	 * Create a new {@link AggregationDefinition} for the given {@link Aggregation}.
+	 *
+	 * @param aggregation must not be {@literal null}.
+	 * @param inputType fallback mapping type in case of untyped aggregation. Can be {@literal null}.
+	 * @return new instance of {@link AggregationDefinition}.
+	 * @since 3.2
+	 */
+	AggregationDefinition createAggregation(Aggregation aggregation, @Nullable Class<?> inputType) {
+		return new AggregationDefinition(aggregation, inputType);
+	}
+
+	/**
+	 * Create a new {@link AggregationDefinition} for the given {@link Aggregation}.
+	 *
+	 * @param aggregation must not be {@literal null}.
+	 * @param aggregationOperationContext the {@link AggregationOperationContext} to use. Can be {@literal null}.
+	 * @return new instance of {@link AggregationDefinition}.
+	 * @since 3.2
+	 */
+	AggregationDefinition createAggregation(Aggregation aggregation,
+			@Nullable AggregationOperationContext aggregationOperationContext) {
+		return new AggregationDefinition(aggregation, aggregationOperationContext);
+	}
+
 	/**
 	 * {@link QueryContext} encapsulates common tasks required to convert a {@link Query} into its MongoDB document
-	 * representation, mapping fieldnames, as well as determinging and applying {@link Collation collations}.
+	 * representation, mapping field names, as well as determining and applying {@link Collation collations}.
 	 *
 	 * @author Christoph Strobl
 	 */
@@ -205,7 +238,7 @@ class QueryOperations {
 		private final Query query;
 
 		/**
-		 * Create new a {@link QueryContext} instance from the given {@literal query} (can be eihter a {@link Query} or a
+		 * Create new a {@link QueryContext} instance from the given {@literal query} (can be either a {@link Query} or a
 		 * plain {@link Document}.
 		 *
 		 * @param query can be {@literal null}.
@@ -258,7 +291,21 @@ class QueryOperations {
 		Document getMappedFields(@Nullable MongoPersistentEntity<?> entity, Class<?> targetType,
 				ProjectionFactory projectionFactory) {
 
-			Document fields = query.getFieldsObject();
+			Document fields = new Document();
+
+			for (Entry<String, Object> entry : query.getFieldsObject().entrySet()) {
+
+				if (entry.getValue() instanceof MongoExpression) {
+
+					AggregationOperationContext ctx = entity == null ? Aggregation.DEFAULT_CONTEXT
+							: new RelaxedTypeBasedAggregationOperationContext(entity.getType(), mappingContext, queryMapper);
+
+					fields.put(entry.getKey(), AggregationExpression.from((MongoExpression) entry.getValue()).toDocument(ctx));
+				} else {
+					fields.put(entry.getKey(), entry.getValue());
+				}
+			}
+
 			Document mappedFields = fields;
 
 			if (entity == null) {
@@ -275,7 +322,7 @@ class QueryOperations {
 						mappingContext.getRequiredPersistentEntity(targetType));
 			}
 
-			if (entity != null && entity.hasTextScoreProperty() && !query.getQueryObject().containsKey("$text")) {
+			if (entity.hasTextScoreProperty() && !query.getQueryObject().containsKey("$text")) {
 				mappedFields.remove(entity.getTextScoreProperty().getFieldName());
 			}
 
@@ -341,7 +388,8 @@ class QueryOperations {
 		}
 
 		@Override
-		Document getMappedFields(@Nullable MongoPersistentEntity<?> entity, Class<?> targetType, ProjectionFactory projectionFactory) {
+		Document getMappedFields(@Nullable MongoPersistentEntity<?> entity, Class<?> targetType,
+				ProjectionFactory projectionFactory) {
 			return getMappedFields(entity);
 		}
 
@@ -565,7 +613,7 @@ class QueryOperations {
 
 		UpdateContext(MappedDocument update, boolean upsert) {
 
-			super(new BasicQuery(new Document(BsonUtils.asMap(update.getIdFilter()))));
+			super(new BasicQuery(BsonUtils.asDocument(update.getIdFilter())));
 			this.multi = false;
 			this.upsert = upsert;
 			this.mappedDocument = update;
@@ -658,7 +706,8 @@ class QueryOperations {
 					: mappedDocument != null ? mappedDocument.getDocument() : getMappedUpdate(domainType);
 
 			Document filterWithShardKey = new Document(filter);
-			getMappedShardKeyFields(domainType).forEach(key -> filterWithShardKey.putIfAbsent(key, shardKeySource.get(key)));
+			getMappedShardKeyFields(domainType)
+					.forEach(key -> filterWithShardKey.putIfAbsent(key, BsonUtils.resolveValue(shardKeySource, key)));
 
 			return filterWithShardKey;
 		}
@@ -709,7 +758,8 @@ class QueryOperations {
 
 			Class<?> type = domainType != null ? domainType : Object.class;
 
-			AggregationOperationContext context = new RelaxedTypeBasedAggregationOperationContext(type, mappingContext, queryMapper);
+			AggregationOperationContext context = new RelaxedTypeBasedAggregationOperationContext(type, mappingContext,
+					queryMapper);
 			return aggregationUtil.createPipeline((AggregationUpdate) update, context);
 		}
 
@@ -759,4 +809,105 @@ class QueryOperations {
 			return multi;
 		}
 	}
+
+	/**
+	 * A value object that encapsulates common tasks required when running {@literal aggregations}.
+	 *
+	 * @since 3.2
+	 */
+	class AggregationDefinition {
+
+		private final Aggregation aggregation;
+		private final Lazy<AggregationOperationContext> aggregationOperationContext;
+		private final Lazy<List<Document>> pipeline;
+		private final @Nullable Class<?> inputType;
+
+		/**
+		 * Creates new instance of {@link AggregationDefinition} extracting the input type from either the
+		 * {@link org.springframework.data.mongodb.core.aggregation.Aggregation} in case of a {@link TypedAggregation} or
+		 * the given {@literal aggregationOperationContext} if present. <br />
+		 * Creates a new {@link AggregationOperationContext} if none given, based on the {@link Aggregation} input type and
+		 * the desired {@link AggregationOptions#getDomainTypeMapping() domain type mapping}. <br />
+		 * Pipelines are mapped on first access of {@link #getAggregationPipeline()} and cached for reuse.
+		 *
+		 * @param aggregation the source aggregation.
+		 * @param aggregationOperationContext can be {@literal null}.
+		 */
+		AggregationDefinition(Aggregation aggregation, @Nullable AggregationOperationContext aggregationOperationContext) {
+
+			this.aggregation = aggregation;
+
+			if (aggregation instanceof TypedAggregation) {
+				this.inputType = ((TypedAggregation<?>) aggregation).getInputType();
+			} else if (aggregationOperationContext instanceof TypeBasedAggregationOperationContext) {
+				this.inputType = ((TypeBasedAggregationOperationContext) aggregationOperationContext).getType();
+			} else {
+				this.inputType = null;
+			}
+
+			this.aggregationOperationContext = Lazy.of(() -> aggregationOperationContext != null ? aggregationOperationContext
+					: aggregationUtil.createAggregationContext(aggregation, getInputType()));
+			this.pipeline = Lazy.of(() -> aggregationUtil.createPipeline(this.aggregation, getAggregationOperationContext()));
+		}
+
+		/**
+		 * Creates new instance of {@link AggregationDefinition} extracting the input type from either the
+		 * {@link org.springframework.data.mongodb.core.aggregation.Aggregation} in case of a {@link TypedAggregation} or
+		 * the given {@literal aggregationOperationContext} if present. <br />
+		 * Creates a new {@link AggregationOperationContext} based on the {@link Aggregation} input type and the desired
+		 * {@link AggregationOptions#getDomainTypeMapping() domain type mapping}. <br />
+		 * Pipelines are mapped on first access of {@link #getAggregationPipeline()} and cached for reuse.
+		 *
+		 * @param aggregation the source aggregation.
+		 * @param inputType can be {@literal null}.
+		 */
+		AggregationDefinition(Aggregation aggregation, @Nullable Class<?> inputType) {
+
+			this.aggregation = aggregation;
+
+			if (aggregation instanceof TypedAggregation) {
+				this.inputType = ((TypedAggregation<?>) aggregation).getInputType();
+			} else {
+				this.inputType = inputType;
+			}
+
+			this.aggregationOperationContext = Lazy
+					.of(() -> aggregationUtil.createAggregationContext(aggregation, getInputType()));
+			this.pipeline = Lazy.of(() -> aggregationUtil.createPipeline(this.aggregation, getAggregationOperationContext()));
+		}
+
+		/**
+		 * Obtain the already mapped pipeline.
+		 *
+		 * @return never {@literal null}.
+		 */
+		List<Document> getAggregationPipeline() {
+			return pipeline.get();
+		}
+
+		/**
+		 * @return {@literal true} if the last aggregation stage is either {@literal $out} or {@literal $merge}.
+		 * @see AggregationPipeline#isOutOrMerge()
+		 */
+		boolean isOutOrMerge() {
+			return aggregation.getPipeline().isOutOrMerge();
+		}
+
+		/**
+		 * Obtain the {@link AggregationOperationContext} used for mapping the pipeline.
+		 *
+		 * @return never {@literal null}.
+		 */
+		AggregationOperationContext getAggregationOperationContext() {
+			return aggregationOperationContext.get();
+		}
+
+		/**
+		 * @return the input type to map the pipeline against. Can be {@literal null}.
+		 */
+		@Nullable
+		Class<?> getInputType() {
+			return inputType;
+		}
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveChangeStreamOperation.java

@@ -71,7 +71,7 @@ public interface ReactiveChangeStreamOperation {
 		/**
 		 * Start listening to changes. The stream will not be completed unless the {@link org.reactivestreams.Subscription}
 		 * is {@link org.reactivestreams.Subscription#cancel() canceled}.
-		 * <p />
+		 * <br />
 		 * However, the stream may become dead, or invalid, if all watched collections, databases are dropped.
 		 */
 		Flux<ChangeStreamEvent<T>> listen();

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveFindOperation.java

@@ -91,10 +91,10 @@ public interface ReactiveFindOperation {
 		 * Get all matching elements using a {@link com.mongodb.CursorType#TailableAwait tailable cursor}. The stream will
 		 * not be completed unless the {@link org.reactivestreams.Subscription} is
 		 * {@link org.reactivestreams.Subscription#cancel() canceled}.
-		 * <p />
+		 * <br />
 		 * However, the stream may become dead, or invalid, if either the query returns no match or the cursor returns the
 		 * document at the "end" of the collection and then the application deletes that document.
-		 * <p />
+		 * <br />
 		 * A stream that is no longer in use must be {@link reactor.core.Disposable#dispose()} disposed} otherwise the
 		 * streams will linger and exhaust resources. <br/>
 		 * <strong>NOTE:</strong> Requires a capped collection.
@@ -106,6 +106,12 @@ public interface ReactiveFindOperation {
 
 		/**
 		 * Get the number of matching elements.
+		 * <br />
+		 * This method uses an
+		 * {@link com.mongodb.reactivestreams.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+		 * aggregation execution} even for empty {@link Query queries} which may have an impact on performance, but
+		 * guarantees shard, session and transaction compliance. In case an inaccurate count satisfies the applications
+		 * needs use {@link ReactiveMongoOperations#estimatedCount(String)} for empty queries instead.
 		 *
 		 * @return {@link Mono} emitting total number of matching elements. Never {@literal null}.
 		 */

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveMongoOperations.java

@@ -59,7 +59,7 @@ import com.mongodb.reactivestreams.client.MongoCollection;
  * Implemented by {@link ReactiveMongoTemplate}. Not often used but a useful option for extensibility and testability
  * (as it can be easily mocked, stubbed, or be the target of a JDK proxy). Command execution using
  * {@link ReactiveMongoOperations} is deferred until subscriber subscribes to the {@link Publisher}.
- * <p />
+ * <br />
  * <strong>NOTE:</strong> Some operations cannot be executed within a MongoDB transaction. Please refer to the MongoDB
  * specific documentation to learn more about <a href="https://docs.mongodb.com/manual/core/transactions/">Multi
  * Document Transactions</a>.
@@ -121,7 +121,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Executes a {@link ReactiveDatabaseCallback} translating any exceptions as necessary.
-	 * <p/>
+	 * <br />
 	 * Allows for returning a result object, that is a domain object or a collection of domain objects.
 	 *
 	 * @param action callback object that specifies the MongoDB actions to perform on the passed in DB instance. Must not
@@ -133,7 +133,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Executes the given {@link ReactiveCollectionCallback} on the entity collection of the specified class.
-	 * <p/>
+	 * <br />
 	 * Allows for returning a result object, that is a domain object or a collection of domain objects.
 	 *
 	 * @param entityClass class that determines the collection to use. Must not be {@literal null}.
@@ -145,7 +145,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Executes the given {@link ReactiveCollectionCallback} on the collection of the given name.
-	 * <p/>
+	 * <br />
 	 * Allows for returning a result object, that is a domain object or a collection of domain objects.
 	 *
 	 * @param collectionName the name of the collection that specifies which {@link MongoCollection} instance will be
@@ -159,7 +159,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Obtain a {@link ClientSession session} bound instance of {@link SessionScoped} binding the {@link ClientSession}
 	 * provided by the given {@link Supplier} to each and every command issued against MongoDB.
-	 * <p />
+	 * <br />
 	 * <strong>Note:</strong> It is up to the caller to manage the {@link ClientSession} lifecycle. Use
 	 * {@link ReactiveSessionScoped#execute(ReactiveSessionCallback, Consumer)} to provide a hook for processing the
 	 * {@link ClientSession} when done.
@@ -178,7 +178,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Obtain a {@link ClientSession session} bound instance of {@link SessionScoped} binding a new {@link ClientSession}
 	 * with given {@literal sessionOptions} to each and every command issued against MongoDB.
-	 * <p />
+	 * <br />
 	 * <strong>Note:</strong> It is up to the caller to manage the {@link ClientSession} lifecycle. Use
 	 * {@link ReactiveSessionScoped#execute(ReactiveSessionCallback, Consumer)} to provide a hook for processing the
 	 * {@link ClientSession} when done.
@@ -192,7 +192,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Obtain a {@link ClientSession session} bound instance of {@link ReactiveSessionScoped} binding the
 	 * {@link ClientSession} provided by the given {@link Publisher} to each and every command issued against MongoDB.
-	 * <p />
+	 * <br />
 	 * <strong>Note:</strong> It is up to the caller to manage the {@link ClientSession} lifecycle. Use
 	 * {@link ReactiveSessionScoped#execute(ReactiveSessionCallback, Consumer)} to provide a hook for processing the
 	 * {@link ClientSession} when done.
@@ -205,7 +205,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Obtain a {@link ClientSession} bound instance of {@link ReactiveMongoOperations}.
-	 * <p />
+	 * <br />
 	 * <strong>Note:</strong> It is up to the caller to manage the {@link ClientSession} lifecycle.
 	 *
 	 * @param session must not be {@literal null}.
@@ -218,7 +218,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * Initiate a new {@link ClientSession} and obtain a {@link ClientSession session} bound instance of
 	 * {@link ReactiveSessionScoped}. Starts the transaction and adds the {@link ClientSession} to each and every command
 	 * issued against MongoDB.
-	 * <p/>
+	 * <br />
 	 * Each {@link ReactiveSessionScoped#execute(ReactiveSessionCallback) execution} initiates a new managed transaction
 	 * that is {@link ClientSession#commitTransaction() committed} on success. Transactions are
 	 * {@link ClientSession#abortTransaction() rolled back} upon errors.
@@ -233,7 +233,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * Obtain a {@link ClientSession session} bound instance of {@link ReactiveSessionScoped}, start the transaction and
 	 * bind the {@link ClientSession} provided by the given {@link Publisher} to each and every command issued against
 	 * MongoDB.
-	 * <p/>
+	 * <br />
 	 * Each {@link ReactiveSessionScoped#execute(ReactiveSessionCallback) execution} initiates a new managed transaction
 	 * that is {@link ClientSession#commitTransaction() committed} on success. Transactions are
 	 * {@link ClientSession#abortTransaction() rolled back} upon errors.
@@ -293,7 +293,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * created on first interaction with the server. Collections can be explicitly created via
 	 * {@link #createCollection(Class)}. Please make sure to check if the collection {@link #collectionExists(Class)
 	 * exists} first.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param collectionName name of the collection.
@@ -303,7 +303,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Check to see if a collection with a name indicated by the entity class exists.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param entityClass class that determines the name of the collection. Must not be {@literal null}.
@@ -313,7 +313,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Check to see if a collection with a given name exists.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param collectionName name of the collection. Must not be {@literal null}.
@@ -323,7 +323,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Drop the collection with the name indicated by the entity class.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param entityClass class that determines the collection to drop/delete. Must not be {@literal null}.
@@ -332,7 +332,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Drop the collection with the given name.
-	 * <p/>
+	 * <br />
 	 * Translate any exceptions as necessary.
 	 *
 	 * @param collectionName name of the collection to drop/delete.
@@ -341,10 +341,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Query for a {@link Flux} of objects of type T from the collection used by the entity class.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your collection does not contain a homogeneous collection of types, this operation will not be an efficient way
 	 * to map objects since the test for class type is done in the client and not on the server.
 	 *
@@ -355,10 +355,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Query for a {@link Flux} of objects of type T from the specified collection.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your collection does not contain a homogeneous collection of types, this operation will not be an efficient way
 	 * to map objects since the test for class type is done in the client and not on the server.
 	 *
@@ -371,10 +371,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Map the results of an ad-hoc query on the collection for the entity class to a single instance of an object of the
 	 * specified type.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -388,10 +388,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Map the results of an ad-hoc query on the specified collection to a single instance of an object of the specified
 	 * type.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -435,10 +435,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Map the results of an ad-hoc query on the collection for the entity class to a {@link Flux} of the specified type.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -451,10 +451,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Map the results of an ad-hoc query on the specified collection to a {@link Flux} of the specified type.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -566,10 +566,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Execute an aggregation operation.
-	 * <p/>
+	 * <br />
 	 * The raw results will be mapped to the given entity class and are returned as stream. The name of the
 	 * inputCollection is derived from the {@link TypedAggregation#getInputType() aggregation input type}.
-	 * <p/>
+	 * <br />
 	 * Aggregation streaming cannot be used with {@link AggregationOptions#isExplain() aggregation explain} nor with
 	 * {@link AggregationOptions#getCursorBatchSize()}. Enabling explanation mode or setting batch size cause
 	 * {@link IllegalArgumentException}.
@@ -584,10 +584,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Execute an aggregation operation.
-	 * <p/>
+	 * <br />
 	 * The raw results will be mapped to the given {@code ouputType}. The name of the inputCollection is derived from the
 	 * {@code inputType}.
-	 * <p/>
+	 * <br />
 	 * Aggregation streaming cannot be used with {@link AggregationOptions#isExplain() aggregation explain} nor with
 	 * {@link AggregationOptions#getCursorBatchSize()}. Enabling explanation mode or setting batch size cause
 	 * {@link IllegalArgumentException}.
@@ -604,9 +604,9 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Execute an aggregation operation.
-	 * <p/>
+	 * <br />
 	 * The raw results will be mapped to the given entity class.
-	 * <p/>
+	 * <br />
 	 * Aggregation streaming cannot be used with {@link AggregationOptions#isExplain() aggregation explain} nor with
 	 * {@link AggregationOptions#getCursorBatchSize()}. Enabling explanation mode or setting batch size cause
 	 * {@link IllegalArgumentException}.
@@ -676,7 +676,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	<T> Flux<GeoResult<T>> geoNear(NearQuery near, Class<T> entityClass, String collectionName);
 
 	/**
-	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify<a/>
+	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify</a>
 	 * to apply provided {@link Update} on documents matching {@link Criteria} of given {@link Query}.
 	 *
 	 * @param query the {@link Query} class that specifies the {@link Criteria} used to find a record and also an optional
@@ -691,7 +691,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	<T> Mono<T> findAndModify(Query query, UpdateDefinition update, Class<T> entityClass);
 
 	/**
-	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify<a/>
+	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify</a>
 	 * to apply provided {@link Update} on documents matching {@link Criteria} of given {@link Query}.
 	 *
 	 * @param query the {@link Query} class that specifies the {@link Criteria} used to find a record and also an optional
@@ -707,7 +707,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	<T> Mono<T> findAndModify(Query query, UpdateDefinition update, Class<T> entityClass, String collectionName);
 
 	/**
-	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify<a/>
+	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify</a>
 	 * to apply provided {@link Update} on documents matching {@link Criteria} of given {@link Query} taking
 	 * {@link FindAndModifyOptions} into account.
 	 *
@@ -725,7 +725,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	<T> Mono<T> findAndModify(Query query, UpdateDefinition update, FindAndModifyOptions options, Class<T> entityClass);
 
 	/**
-	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify<a/>
+	 * Triggers <a href="https://docs.mongodb.org/manual/reference/method/db.collection.findAndModify/">findAndModify</a>
 	 * to apply provided {@link Update} on documents matching {@link Criteria} of given {@link Query} taking
 	 * {@link FindAndModifyOptions} into account.
 	 *
@@ -746,7 +746,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement}
 	 * document. <br />
 	 * Options are defaulted to {@link FindAndReplaceOptions#empty()}. <br />
@@ -764,7 +764,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement}
 	 * document. <br />
 	 * Options are defaulted to {@link FindAndReplaceOptions#empty()}. <br />
@@ -783,7 +783,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account. <br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -803,7 +803,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account. <br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -825,7 +825,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account. <br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -849,7 +849,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account. <br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -876,7 +876,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Triggers
-	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace<a/>
+	 * <a href="https://docs.mongodb.com/manual/reference/method/db.collection.findOneAndReplace/">findOneAndReplace</a>
 	 * to replace a single document matching {@link Criteria} of given {@link Query} with the {@code replacement} document
 	 * taking {@link FindAndReplaceOptions} into account. <br />
 	 * <strong>NOTE:</strong> The replacement entity must not hold an {@literal id}.
@@ -902,9 +902,9 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * Map the results of an ad-hoc query on the collection for the entity type to a single instance of an object of the
 	 * specified type. The first document that matches the query is returned and also removed from the collection in the
 	 * database.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -918,10 +918,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Map the results of an ad-hoc query on the specified collection to a single instance of an object of the specified
 	 * type. The first document that matches the query is returned and also removed from the collection in the database.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -940,6 +940,12 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
 	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
 	 * count all matches.
+	 * <br />
+	 * This method uses an
+	 * {@link com.mongodb.reactivestreams.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} even for empty {@link Query queries} which may have an impact on performance, but guarantees
+	 * shard, session and transaction compliance. In case an inaccurate count satisfies the applications needs use
+	 * {@link #estimatedCount(Class)} for empty queries instead.
 	 *
 	 * @param query the {@link Query} class that specifies the criteria used to find documents. Must not be
 	 *          {@literal null}.
@@ -956,6 +962,12 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
 	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
 	 * count all matches.
+	 * <br />
+	 * This method uses an
+	 * {@link com.mongodb.reactivestreams.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} even for empty {@link Query queries} which may have an impact on performance, but guarantees
+	 * shard, session and transaction compliance. In case an inaccurate count satisfies the applications needs use
+	 * {@link #estimatedCount(String)} for empty queries instead.
 	 *
 	 * @param query the {@link Query} class that specifies the criteria used to find documents.
 	 * @param collectionName must not be {@literal null} or empty.
@@ -971,6 +983,12 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * influence on the resulting number of documents found as those values are passed on to the server and potentially
 	 * limit the range and order within which the server performs the count operation. Use an {@literal unpaged} query to
 	 * count all matches.
+	 * <br />
+	 * This method uses an
+	 * {@link com.mongodb.reactivestreams.client.MongoCollection#countDocuments(org.bson.conversions.Bson, com.mongodb.client.model.CountOptions)
+	 * aggregation execution} even for empty {@link Query queries} which may have an impact on performance, but guarantees
+	 * shard, session and transaction compliance. In case an inaccurate count satisfies the applications needs use
+	 * {@link #estimatedCount(String)} for empty queries instead.
 	 *
 	 * @param query the {@link Query} class that specifies the criteria used to find documents. Must not be
 	 *          {@literal null}.
@@ -983,6 +1001,9 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Estimate the number of documents, in the collection {@link #getCollectionName(Class) identified by the given type},
 	 * based on collection statistics.
+	 * <br />
+	 * Please make sure to read the MongoDB reference documentation about limitations on eg. sharded cluster or inside
+	 * transactions.
 	 *
 	 * @param entityClass must not be {@literal null}.
 	 * @return a {@link Mono} emitting the estimated number of documents.
@@ -996,6 +1017,9 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Estimate the number of documents in the given collection based on collection statistics.
+	 * <br />
+	 * Please make sure to read the MongoDB reference documentation about limitations on eg. sharded cluster or inside
+	 * transactions.
 	 *
 	 * @param collectionName must not be {@literal null}.
 	 * @return a {@link Mono} emitting the estimated number of documents.
@@ -1005,34 +1029,39 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Insert the object into the collection for the entity type of the object to save.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}.
-	 * <p/>
+	 * <br />
 	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
 	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
 	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
 	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
 	 * Type Conversion"</a> for more details.
-	 * <p/>
-	 * <p/>
+	 * <br />
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.
+	 * <br />
+	 * The {@code objectToSave} must not be collection-like.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
 	 * @return the inserted object.
+	 * @throws IllegalArgumentException in case the {@code objectToSave} is collection-like.
 	 */
 	<T> Mono<T> insert(T objectToSave);
 
 	/**
 	 * Insert the object into the specified collection.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.
+	 * <br />
+	 * The {@code objectToSave} must not be collection-like.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
 	 * @param collectionName name of the collection to store the object in. Must not be {@literal null}.
 	 * @return the inserted object.
+	 * @throws IllegalArgumentException in case the {@code objectToSave} is collection-like.
 	 */
 	<T> Mono<T> insert(T objectToSave, String collectionName);
 
@@ -1065,16 +1094,15 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 
 	/**
 	 * Insert the object into the collection for the entity type of the object to save.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}.
-	 * <p/>
+	 * <br />
 	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
 	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
 	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
 	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
 	 * Type Conversion"</a> for more details.
-	 * <p/>
-	 * <p/>
+	 * <br />
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
@@ -1112,52 +1140,54 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Save the object to the collection for the entity type of the object to save. This will perform an insert if the
 	 * object is not already present, that is an 'upsert'.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
 	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
 	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
 	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
 	 * Type Conversion"</a> for more details.
+	 * <br />
+	 * The {@code objectToSave} must not be collection-like.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
 	 * @return the saved object.
+	 * @throws IllegalArgumentException in case the {@code objectToSave} is collection-like.
 	 */
 	<T> Mono<T> save(T objectToSave);
 
 	/**
 	 * Save the object to the specified collection. This will perform an insert if the object is not already present, that
 	 * is an 'upsert'.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
 	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
-	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See <a
-	 * https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation">Spring's Type
-	 * Conversion"</a> for more details.
+	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API.
+	 * See <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation">Spring's Type Conversion</a> for more details.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
 	 * @param collectionName name of the collection to store the object in. Must not be {@literal null}.
 	 * @return the saved object.
+	 * @throws IllegalArgumentException in case the {@code objectToSave} is collection-like.
 	 */
 	<T> Mono<T> save(T objectToSave, String collectionName);
 
 	/**
 	 * Save the object to the collection for the entity type of the object to save. This will perform an insert if the
 	 * object is not already present, that is an 'upsert'.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
 	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
-	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See
-	 * <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation" > Spring's
-	 * Type Conversion"</a> for more details.
+	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API.
+	 * See <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation"> Spring's Type Conversion</a> for more details.
 	 *
 	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
 	 * @return the saved object.
@@ -1167,17 +1197,16 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	/**
 	 * Save the object to the specified collection. This will perform an insert if the object is not already present, that
 	 * is an 'upsert'.
-	 * <p/>
+	 * <br />
 	 * The object is converted to the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * If your object has an "Id' property, it will be set with the generated Id from MongoDB. If your Id property is a
 	 * String then MongoDB ObjectId will be used to populate that string. Otherwise, the conversion from ObjectId to your
-	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API. See <a
-	 * https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation">Spring's Type
-	 * Conversion"</a> for more details.
+	 * property type will be handled by Spring's BeanWrapper class that leverages Type Conversion API.
+	 * See <a href="https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#validation">Spring's Type Conversion</a> for more details.
 	 *
-	 * @param objectToSave the object to store in the collection. Must not be {@literal null}.
+	 * @param objectToSave the object to store in the collReactiveMongoOperationsection. Must not be {@literal null}.
 	 * @param collectionName name of the collection to store the object in. Must not be {@literal null}.
 	 * @return the saved object.
 	 */
@@ -1449,10 +1478,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * type. The stream uses a {@link com.mongodb.CursorType#TailableAwait tailable} cursor that may be an infinite
 	 * stream. The stream will not be completed unless the {@link org.reactivestreams.Subscription} is
 	 * {@link Subscription#cancel() canceled}.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -1468,10 +1497,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * type. The stream uses a {@link com.mongodb.CursorType#TailableAwait tailable} cursor that may be an infinite
 	 * stream. The stream will not be completed unless the {@link org.reactivestreams.Subscription} is
 	 * {@link Subscription#cancel() canceled}.
-	 * <p/>
+	 * <br />
 	 * The object is converted from the MongoDB native representation using an instance of {@see MongoConverter}. Unless
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
-	 * <p/>
+	 * <br />
 	 * The query is specified as a {@link Query} which can be created either using the {@link BasicQuery} or the more
 	 * feature rich {@link Query}.
 	 *
@@ -1488,10 +1517,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * the configured default database via the reactive infrastructure. Use the optional provided {@link Aggregation} to
 	 * filter events. The stream will not be completed unless the {@link org.reactivestreams.Subscription} is
 	 * {@link Subscription#cancel() canceled}.
-	 * <p />
+	 * <br />
 	 * The {@link ChangeStreamEvent#getBody()} is mapped to the {@literal resultType} while the
 	 * {@link ChangeStreamEvent#getRaw()} contains the unmodified payload.
-	 * <p />
+	 * <br />
 	 * Use {@link ChangeStreamOptions} to set arguments like {@link ChangeStreamOptions#getResumeToken() the resumseToken}
 	 * for resuming change streams.
 	 *
@@ -1512,10 +1541,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * the given collection via the reactive infrastructure. Use the optional provided {@link Aggregation} to filter
 	 * events. The stream will not be completed unless the {@link org.reactivestreams.Subscription} is
 	 * {@link Subscription#cancel() canceled}.
-	 * <p />
+	 * <br />
 	 * The {@link ChangeStreamEvent#getBody()} is mapped to the {@literal resultType} while the
 	 * {@link ChangeStreamEvent#getRaw()} contains the unmodified payload.
-	 * <p />
+	 * <br />
 	 * Use {@link ChangeStreamOptions} to set arguments like {@link ChangeStreamOptions#getResumeToken() the resumseToken}
 	 * for resuming change streams.
 	 *
@@ -1537,10 +1566,10 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * Subscribe to a MongoDB <a href="https://docs.mongodb.com/manual/changeStreams/">Change Stream</a> via the reactive
 	 * infrastructure. Use the optional provided {@link Aggregation} to filter events. The stream will not be completed
 	 * unless the {@link org.reactivestreams.Subscription} is {@link Subscription#cancel() canceled}.
-	 * <p />
+	 * <br />
 	 * The {@link ChangeStreamEvent#getBody()} is mapped to the {@literal resultType} while the
 	 * {@link ChangeStreamEvent#getRaw()} contains the unmodified payload.
-	 * <p />
+	 * <br />
 	 * Use {@link ChangeStreamOptions} to set arguments like {@link ChangeStreamOptions#getResumeToken() the resumseToken}
 	 * for resuming change streams.
 	 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveMongoTemplate.java

@@ -17,13 +17,20 @@ package org.springframework.data.mongodb.core;
 
 import static org.springframework.data.mongodb.core.query.SerializationUtils.*;
 
-import org.springframework.data.mongodb.core.aggregation.RelaxedTypeBasedAggregationOperationContext;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.util.function.Tuple2;
 import reactor.util.function.Tuples;
 
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
 import java.util.function.Function;
@@ -53,6 +60,7 @@ import org.springframework.data.convert.EntityReader;
 import org.springframework.data.geo.Distance;
 import org.springframework.data.geo.GeoResult;
 import org.springframework.data.geo.Metric;
+import org.springframework.data.mapping.MappingException;
 import org.springframework.data.mapping.PersistentEntity;
 import org.springframework.data.mapping.callback.ReactiveEntityCallbacks;
 import org.springframework.data.mapping.context.MappingContext;
@@ -62,6 +70,7 @@ import org.springframework.data.mongodb.ReactiveMongoDatabaseFactory;
 import org.springframework.data.mongodb.ReactiveMongoDatabaseUtils;
 import org.springframework.data.mongodb.SessionSynchronization;
 import org.springframework.data.mongodb.core.EntityOperations.AdaptibleEntity;
+import org.springframework.data.mongodb.core.QueryOperations.AggregationDefinition;
 import org.springframework.data.mongodb.core.QueryOperations.CountContext;
 import org.springframework.data.mongodb.core.QueryOperations.DeleteContext;
 import org.springframework.data.mongodb.core.QueryOperations.DistinctQueryContext;
@@ -71,6 +80,7 @@ import org.springframework.data.mongodb.core.aggregation.Aggregation;
 import org.springframework.data.mongodb.core.aggregation.AggregationOperationContext;
 import org.springframework.data.mongodb.core.aggregation.AggregationOptions;
 import org.springframework.data.mongodb.core.aggregation.PrefixingDelegatingAggregationOperationContext;
+import org.springframework.data.mongodb.core.aggregation.RelaxedTypeBasedAggregationOperationContext;
 import org.springframework.data.mongodb.core.aggregation.TypeBasedAggregationOperationContext;
 import org.springframework.data.mongodb.core.aggregation.TypedAggregation;
 import org.springframework.data.mongodb.core.convert.DbRefResolver;
@@ -100,6 +110,7 @@ import org.springframework.data.mongodb.core.query.NearQuery;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.core.query.UpdateDefinition;
 import org.springframework.data.mongodb.core.query.UpdateDefinition.ArrayFilter;
+import org.springframework.data.mongodb.core.timeseries.Granularity;
 import org.springframework.data.mongodb.core.validation.Validator;
 import org.springframework.data.mongodb.util.BsonUtils;
 import org.springframework.data.projection.SpelAwareProxyProjectionFactory;
@@ -156,18 +167,6 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 
 	private static final Logger LOGGER = LoggerFactory.getLogger(ReactiveMongoTemplate.class);
 	private static final WriteResultChecking DEFAULT_WRITE_RESULT_CHECKING = WriteResultChecking.NONE;
-	private static final Collection<Class<?>> ITERABLE_CLASSES;
-
-	static {
-
-		Set<Class<?>> iterableClasses = new HashSet<>();
-		iterableClasses.add(List.class);
-		iterableClasses.add(Collection.class);
-		iterableClasses.add(Iterator.class);
-		iterableClasses.add(Publisher.class);
-
-		ITERABLE_CLASSES = Collections.unmodifiableCollection(iterableClasses);
-	}
 
 	private final MongoConverter mongoConverter;
 	private final MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext;
@@ -363,7 +362,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 * Set the {@link ReactiveEntityCallbacks} instance to use when invoking
 	 * {@link org.springframework.data.mapping.callback.EntityCallback callbacks} like the
 	 * {@link ReactiveBeforeSaveCallback}.
-	 * <p />
+	 * <br />
 	 * Overrides potentially existing {@link ReactiveEntityCallbacks}.
 	 *
 	 * @param entityCallbacks must not be {@literal null}.
@@ -667,7 +666,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 * @see org.springframework.data.mongodb.core.ReactiveMongoOperations#createCollection(java.lang.Class)
 	 */
 	public <T> Mono<MongoCollection<Document>> createCollection(Class<T> entityClass) {
-		return createCollection(entityClass, CollectionOptions.empty());
+		return createCollection(entityClass, operations.forType(entityClass).getCollectionOptions());
 	}
 
 	/*
@@ -946,9 +945,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 
 		Assert.notNull(aggregation, "Aggregation pipeline must not be null!");
 
-		AggregationOperationContext context = new TypeBasedAggregationOperationContext(aggregation.getInputType(),
-				mappingContext, queryMapper);
-		return aggregate(aggregation, inputCollectionName, outputType, context);
+		return doAggregate(aggregation, inputCollectionName, aggregation.getInputType(), outputType);
 	}
 
 	/*
@@ -966,9 +963,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 */
 	@Override
 	public <O> Flux<O> aggregate(Aggregation aggregation, Class<?> inputType, Class<O> outputType) {
-
-		return aggregate(aggregation, getCollectionName(inputType), outputType,
-				new TypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper));
+		return doAggregate(aggregation, getCollectionName(inputType), inputType, outputType);
 	}
 
 	/*
@@ -977,45 +972,34 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 */
 	@Override
 	public <O> Flux<O> aggregate(Aggregation aggregation, String collectionName, Class<O> outputType) {
-		return aggregate(aggregation, collectionName, outputType, null);
+		return doAggregate(aggregation, collectionName, null, outputType);
 	}
 
-	/**
-	 * @param aggregation must not be {@literal null}.
-	 * @param collectionName must not be {@literal null}.
-	 * @param outputType must not be {@literal null}.
-	 * @param context can be {@literal null} and will be defaulted to {@link Aggregation#DEFAULT_CONTEXT}.
-	 * @return never {@literal null}.
-	 */
-	protected <O> Flux<O> aggregate(Aggregation aggregation, String collectionName, Class<O> outputType,
-			@Nullable AggregationOperationContext context) {
+	protected <O> Flux<O> doAggregate(Aggregation aggregation, String collectionName, @Nullable Class<?> inputType,
+			Class<O> outputType) {
 
 		Assert.notNull(aggregation, "Aggregation pipeline must not be null!");
 		Assert.hasText(collectionName, "Collection name must not be null or empty!");
 		Assert.notNull(outputType, "Output type must not be null!");
 
-		AggregationUtil aggregationUtil = new AggregationUtil(queryMapper, mappingContext);
-		AggregationOperationContext rootContext = aggregationUtil.prepareAggregationContext(aggregation, context);
-
 		AggregationOptions options = aggregation.getOptions();
-		List<Document> pipeline = aggregationUtil.createPipeline(aggregation, rootContext);
-
 		Assert.isTrue(!options.isExplain(), "Cannot use explain option with streaming!");
 
+		AggregationDefinition ctx = queryOperations.createAggregation(aggregation, inputType);
+
 		if (LOGGER.isDebugEnabled()) {
-			LOGGER.debug("Streaming aggregation: {} in collection {}", serializeToJsonSafely(pipeline), collectionName);
+			LOGGER.debug("Streaming aggregation: {} in collection {}", serializeToJsonSafely(ctx.getAggregationPipeline()),
+					collectionName);
 		}
 
 		ReadDocumentCallback<O> readCallback = new ReadDocumentCallback<>(mongoConverter, outputType, collectionName);
-		return execute(collectionName,
-				collection -> aggregateAndMap(collection, pipeline, aggregation.getPipeline().isOutOrMerge(), options,
-						readCallback,
-						aggregation instanceof TypedAggregation ? ((TypedAggregation<?>) aggregation).getInputType() : null));
+		return execute(collectionName, collection -> aggregateAndMap(collection, ctx.getAggregationPipeline(),
+				ctx.isOutOrMerge(), options, readCallback, ctx.getInputType()));
 	}
 
 	private <O> Flux<O> aggregateAndMap(MongoCollection<Document> collection, List<Document> pipeline,
-			boolean isOutOrMerge,
-			AggregationOptions options, ReadDocumentCallback<O> readCallback, @Nullable Class<?> inputType) {
+			boolean isOutOrMerge, AggregationOptions options, ReadDocumentCallback<O> readCallback,
+			@Nullable Class<?> inputType) {
 
 		AggregatePublisher<Document> cursor = collection.aggregate(pipeline, Document.class)
 				.allowDiskUse(options.isAllowDiskUse());
@@ -2522,6 +2506,20 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 			result.validationOptions(validationOptions);
 		});
 
+		collectionOptions.getTimeSeriesOptions().map(operations.forType(entityType)::mapTimeSeriesOptions).ifPresent(it -> {
+
+			TimeSeriesOptions options = new TimeSeriesOptions(it.getTimeField());
+
+			if (StringUtils.hasText(it.getMetaField())) {
+				options.metaField(it.getMetaField());
+			}
+			if (!Granularity.DEFAULT.equals(it.getGranularity())) {
+				options.granularity(TimeSeriesGranularity.valueOf(it.getGranularity().name().toUpperCase()));
+			}
+
+			result.timeSeriesOptions(options);
+		});
+
 		return result;
 	}
 
@@ -2539,7 +2537,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	/**
 	 * Map the results of an ad-hoc query on the default MongoDB collection to an object using the template's converter.
 	 * The first document that matches the query is returned and also removed from the collection in the database.
-	 * <p/>
+	 * <br />
 	 * The query document is specified as a standard Document and so is the fields specification.
 	 *
 	 * @param collectionName name of the collection to retrieve the objects from
@@ -2682,13 +2680,27 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 		}
 	}
 
-	protected void ensureNotIterable(Object o) {
+	/**
+	 * Ensure the given {@literal source} is not an {@link java.lang.reflect.Array}, {@link Collection} or
+	 * {@link Iterator}.
+	 *
+	 * @param source can be {@literal null}.
+	 * @deprecated since 3.2. Call {@link #ensureNotCollectionLike(Object)} instead.
+	 */
+	protected void ensureNotIterable(@Nullable Object source) {
+		ensureNotCollectionLike(source);
+	}
 
-		boolean isIterable = o.getClass().isArray()
-				|| ITERABLE_CLASSES.stream().anyMatch(iterableClass -> iterableClass.isAssignableFrom(o.getClass())
-						|| o.getClass().getName().equals(iterableClass.getName()));
+	/**
+	 * Ensure the given {@literal source} is not an {@link java.lang.reflect.Array}, {@link Collection} or
+	 * {@link Iterator}.
+	 *
+	 * @param source can be {@literal null}.
+	 * @since 3.2.
+	 */
+	protected void ensureNotCollectionLike(@Nullable Object source) {
 
-		if (isIterable) {
+		if (EntityOperations.isCollectionLike(source) || source instanceof Publisher) {
 			throw new IllegalArgumentException("Cannot use a collection here.");
 		}
 	}
@@ -2730,6 +2742,14 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 		return potentiallyForceAcknowledgedWrite(wc);
 	}
 
+	/**
+	 * @return the {@link MongoDatabaseFactory} in use.
+	 * @since 3.1.4
+	 */
+	public ReactiveMongoDatabaseFactory getMongoDatabaseFactory() {
+		return mongoDatabaseFactory;
+	}
+
 	@Nullable
 	private WriteConcern potentiallyForceAcknowledgedWrite(@Nullable WriteConcern wc) {
 
@@ -3157,13 +3177,14 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 
 			maybeEmitEvent(new AfterLoadEvent<>(document, type, collectionName));
 
-			T source = reader.read(type, document);
-			if (source != null) {
-				maybeEmitEvent(new AfterConvertEvent<>(document, source, collectionName));
-				return maybeCallAfterConvert(source, document, collectionName);
+			T entity = reader.read(type, document);
+
+			if (entity == null) {
+				throw new MappingException(String.format("EntityReader %s returned null", reader));
 			}
 
-			return Mono.empty();
+			maybeEmitEvent(new AfterConvertEvent<>(document, entity, collectionName));
+			return maybeCallAfterConvert(entity, document, collectionName);
 		}
 	}
 
@@ -3201,16 +3222,17 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 
 			maybeEmitEvent(new AfterLoadEvent<>(document, typeToRead, collectionName));
 
-			Object source = reader.read(typeToRead, document);
-			Object result = targetType.isInterface() ? projectionFactory.createProjection(targetType, source) : source;
+			Object entity = reader.read(typeToRead, document);
 
-			T castEntity = (T) result;
-			if (castEntity != null) {
-				maybeEmitEvent(new AfterConvertEvent<>(document, castEntity, collectionName));
-				return maybeCallAfterConvert(castEntity, document, collectionName);
+			if (entity == null) {
+				throw new MappingException(String.format("EntityReader %s returned null", reader));
 			}
 
-			return Mono.empty();
+			Object result = targetType.isInterface() ? projectionFactory.createProjection(targetType, entity) : entity;
+
+			T castEntity = (T) result;
+			maybeEmitEvent(new AfterConvertEvent<>(document, castEntity, collectionName));
+			return maybeCallAfterConvert(castEntity, document, collectionName);
 		}
 	}
 
@@ -3368,7 +3390,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	/**
 	 * {@link MongoTemplate} extension bound to a specific {@link ClientSession} that is applied when interacting with the
 	 * server through the driver API.
-	 * <p />
+	 * <br />
 	 * The prepare steps for {@link MongoDatabase} and {@link MongoCollection} proxy the target and invoke the desired
 	 * target method matching the actual arguments plus a {@link ClientSession}.
 	 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveSessionCallback.java

@@ -32,7 +32,7 @@ public interface ReactiveSessionCallback<T> {
 	/**
 	 * Execute operations against a MongoDB instance via session bound {@link ReactiveMongoOperations}. The session is
 	 * inferred directly into the operation so that no further interaction is necessary.
-	 * <p />
+	 * <br />
 	 * Please note that only Spring Data-specific abstractions like {@link ReactiveMongoOperations#find(Query, Class)} and
 	 * others are enhanced with the {@link com.mongodb.session.ClientSession}. When obtaining plain MongoDB gateway
 	 * objects like {@link com.mongodb.reactivestreams.client.MongoCollection} or

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ReactiveSessionScoped.java

@@ -33,7 +33,7 @@ public interface ReactiveSessionScoped {
 
 	/**
 	 * Executes the given {@link ReactiveSessionCallback} within the {@link com.mongodb.session.ClientSession}.
-	 * <p/>
+	 * <br />
 	 * It is up to the caller to make sure the {@link com.mongodb.session.ClientSession} is {@link ClientSession#close()
 	 * closed} when done.
 	 *
@@ -47,7 +47,7 @@ public interface ReactiveSessionScoped {
 
 	/**
 	 * Executes the given {@link ReactiveSessionCallback} within the {@link com.mongodb.session.ClientSession}.
-	 * <p/>
+	 * <br />
 	 * It is up to the caller to make sure the {@link com.mongodb.session.ClientSession} is {@link ClientSession#close()
 	 * closed} when done.
 	 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/ScriptOperations.java

@@ -23,7 +23,7 @@ import org.springframework.lang.Nullable;
 
 
 /**
- * Script operations on {@link com.mongodb.DB} level. Allows interaction with server side JavaScript functions.
+ * Script operations on {@link com.mongodb.client.MongoDatabase} level. Allows interaction with server side JavaScript functions.
  *
  * @author Christoph Strobl
  * @author Oliver Gierke
@@ -72,10 +72,10 @@ public interface ScriptOperations {
 	Object call(String scriptName, Object... args);
 
 	/**
-	 * Checks {@link DB} for existence of {@link ServerSideJavaScript} with given name.
+	 * Checks {@link com.mongodb.client.MongoDatabase} for existence of {@literal ServerSideJavaScript} with given name.
 	 *
 	 * @param scriptName must not be {@literal null} or empty.
-	 * @return false if no {@link ServerSideJavaScript} with given name exists.
+	 * @return false if no {@literal ServerSideJavaScript} with given name exists.
 	 */
 	boolean exists(String scriptName);
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/SessionCallback.java

@@ -31,7 +31,7 @@ public interface SessionCallback<T> {
 	/**
 	 * Execute operations against a MongoDB instance via session bound {@link MongoOperations}. The session is inferred
 	 * directly into the operation so that no further interaction is necessary.
-	 * <p />
+	 * <br />
 	 * Please note that only Spring Data-specific abstractions like {@link MongoOperations#find(Query, Class)} and others
 	 * are enhanced with the {@link com.mongodb.session.ClientSession}. When obtaining plain MongoDB gateway objects like
 	 * {@link com.mongodb.client.MongoCollection} or {@link com.mongodb.client.MongoDatabase} via eg.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/SessionScoped.java

@@ -23,7 +23,7 @@ import com.mongodb.client.ClientSession;
 
 /**
  * Gateway interface to execute {@link ClientSession} bound operations against MongoDB via a {@link SessionCallback}.
- * <p />
+ * <br />
  * The very same bound {@link ClientSession} is used for all invocations of {@code execute} on the instance.
  *
  * @author Christoph Strobl
@@ -34,7 +34,7 @@ public interface SessionScoped {
 
 	/**
 	 * Executes the given {@link SessionCallback} within the {@link com.mongodb.session.ClientSession}.
-	 * <p/>
+	 * <br />
 	 * It is up to the caller to make sure the {@link com.mongodb.session.ClientSession} is {@link ClientSession#close()
 	 * closed} when done.
 	 *
@@ -49,7 +49,7 @@ public interface SessionScoped {
 
 	/**
 	 * Executes the given {@link SessionCallback} within the {@link com.mongodb.session.ClientSession}.
-	 * <p/>
+	 * <br />
 	 * It is up to the caller to make sure the {@link com.mongodb.session.ClientSession} is {@link ClientSession#close()
 	 * closed} when done.
 	 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AccumulatorOperators.java

@@ -142,11 +142,118 @@ public class AccumulatorOperators {
 			return usesFieldRef() ? StdDevSamp.stdDevSampOf(fieldReference) : StdDevSamp.stdDevSampOf(expression);
 		}
 
+		/**
+		 * Creates new {@link AggregationExpression} that uses the previous input (field/expression) and the value of the
+		 * given field to calculate the population covariance of the two.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link CovariancePop}.
+		 * @since 3.3
+		 */
+		public CovariancePop covariancePop(String fieldReference) {
+			return covariancePop().and(fieldReference);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that uses the previous input (field/expression) and the result of the
+		 * given {@link AggregationExpression expression} to calculate the population covariance of the two.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link CovariancePop}.
+		 * @since 3.3
+		 */
+		public CovariancePop covariancePop(AggregationExpression expression) {
+			return covariancePop().and(expression);
+		}
+
+		private CovariancePop covariancePop() {
+			return usesFieldRef() ? CovariancePop.covariancePopOf(fieldReference) : CovariancePop.covariancePopOf(expression);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that uses the previous input (field/expression) and the value of the
+		 * given field to calculate the sample covariance of the two.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link CovariancePop}.
+		 * @since 3.3
+		 */
+		public CovarianceSamp covarianceSamp(String fieldReference) {
+			return covarianceSamp().and(fieldReference);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that uses the previous input (field/expression) and the result of the
+		 * given {@link AggregationExpression expression} to calculate the sample covariance of the two.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link CovariancePop}.
+		 * @since 3.3
+		 */
+		public CovarianceSamp covarianceSamp(AggregationExpression expression) {
+			return covarianceSamp().and(expression);
+		}
+
+		private CovarianceSamp covarianceSamp() {
+			return usesFieldRef() ? CovarianceSamp.covarianceSampOf(fieldReference)
+					: CovarianceSamp.covarianceSampOf(expression);
+		}
+
+		/**
+		 * Creates new {@link ExpMovingAvgBuilder} that to build {@link AggregationExpression expMovingAvg} that calculates
+		 * the exponential moving average of numeric values
+		 *
+		 * @return new instance of {@link ExpMovingAvg}.
+		 * @since 3.3
+		 */
+		public ExpMovingAvgBuilder expMovingAvg() {
+
+			ExpMovingAvg expMovingAvg = usesFieldRef() ? ExpMovingAvg.expMovingAvgOf(fieldReference)
+					: ExpMovingAvg.expMovingAvgOf(expression);
+			return new ExpMovingAvgBuilder() {
+
+				@Override
+				public ExpMovingAvg historicalDocuments(int numberOfHistoricalDocuments) {
+					return expMovingAvg.n(numberOfHistoricalDocuments);
+				}
+
+				@Override
+				public ExpMovingAvg alpha(double exponentialDecayValue) {
+					return expMovingAvg.alpha(exponentialDecayValue);
+				}
+			};
+		}
+
 		private boolean usesFieldRef() {
 			return fieldReference != null;
 		}
 	}
 
+	/**
+	 * Builder for {@link ExpMovingAvg}.
+	 *
+	 * @since 3.3
+	 */
+	public interface ExpMovingAvgBuilder {
+
+		/**
+		 * Define the number of historical documents with significant mathematical weight.
+		 *
+		 * @param numberOfHistoricalDocuments
+		 * @return new instance of {@link ExpMovingAvg}.
+		 */
+		ExpMovingAvg historicalDocuments(int numberOfHistoricalDocuments);
+
+		/**
+		 * Define the exponential decay value.
+		 *
+		 * @param exponentialDecayValue
+		 * @return new instance of {@link ExpMovingAvg}.
+		 */
+		ExpMovingAvg alpha(double exponentialDecayValue);
+
+	}
+
 	/**
 	 * {@link AggregationExpression} for {@code $sum}.
 	 *
@@ -658,4 +765,185 @@ public class AccumulatorOperators {
 			return super.toDocument(value, context);
 		}
 	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $covariancePop}.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class CovariancePop extends AbstractAggregationExpression {
+
+		private CovariancePop(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates new {@link CovariancePop}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link CovariancePop}.
+		 */
+		public static CovariancePop covariancePopOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+			return new CovariancePop(asFields(fieldReference));
+		}
+
+		/**
+		 * Creates new {@link CovariancePop}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link CovariancePop}.
+		 */
+		public static CovariancePop covariancePopOf(AggregationExpression expression) {
+			return new CovariancePop(Collections.singletonList(expression));
+		}
+
+		/**
+		 * Creates new {@link CovariancePop} with all previously added arguments appending the given one.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link CovariancePop}.
+		 */
+		public CovariancePop and(String fieldReference) {
+			return new CovariancePop(append(asFields(fieldReference)));
+		}
+
+		/**
+		 * Creates new {@link CovariancePop} with all previously added arguments appending the given one.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link CovariancePop}.
+		 */
+		public CovariancePop and(AggregationExpression expression) {
+			return new CovariancePop(append(expression));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$covariancePop";
+		}
+	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $covarianceSamp}.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class CovarianceSamp extends AbstractAggregationExpression {
+
+		private CovarianceSamp(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates new {@link CovarianceSamp}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link CovarianceSamp}.
+		 */
+		public static CovarianceSamp covarianceSampOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+			return new CovarianceSamp(asFields(fieldReference));
+		}
+
+		/**
+		 * Creates new {@link CovarianceSamp}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link CovarianceSamp}.
+		 */
+		public static CovarianceSamp covarianceSampOf(AggregationExpression expression) {
+			return new CovarianceSamp(Collections.singletonList(expression));
+		}
+
+		/**
+		 * Creates new {@link CovarianceSamp} with all previously added arguments appending the given one.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link CovarianceSamp}.
+		 */
+		public CovarianceSamp and(String fieldReference) {
+			return new CovarianceSamp(append(asFields(fieldReference)));
+		}
+
+		/**
+		 * Creates new {@link CovarianceSamp} with all previously added arguments appending the given one.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link CovarianceSamp}.
+		 */
+		public CovarianceSamp and(AggregationExpression expression) {
+			return new CovarianceSamp(append(expression));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$covarianceSamp";
+		}
+	}
+
+	/**
+	 * {@link ExpMovingAvg} calculates the exponential moving average of numeric values.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class ExpMovingAvg extends AbstractAggregationExpression {
+
+		private ExpMovingAvg(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Create a new {@link ExpMovingAvg} by defining the field holding the value to be used as input.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link ExpMovingAvg}.
+		 */
+		public static ExpMovingAvg expMovingAvgOf(String fieldReference) {
+			return new ExpMovingAvg(Collections.singletonMap("input", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Create a new {@link ExpMovingAvg} by defining the {@link AggregationExpression expression} to compute the value
+		 * to be used as input.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link ExpMovingAvg}.
+		 */
+		public static ExpMovingAvg expMovingAvgOf(AggregationExpression expression) {
+			return new ExpMovingAvg(Collections.singletonMap("input", expression));
+		}
+
+		/**
+		 * Define the number of historical documents with significant mathematical weight. <br />
+		 * Specify either {@link #n(int) N} or {@link #alpha(double) aplha}. Not both!
+		 *
+		 * @param numberOfHistoricalDocuments
+		 * @return new instance of {@link ExpMovingAvg}.
+		 */
+		public ExpMovingAvg n/*umber of historical documents*/(int numberOfHistoricalDocuments) {
+			return new ExpMovingAvg(append("N", numberOfHistoricalDocuments));
+		}
+
+		/**
+		 * Define the exponential decay value. <br />
+		 * Specify either {@link #alpha(double) aplha} or {@link #n(int) N}. Not both!
+		 *
+		 * @param exponentialDecayValue
+		 * @return new instance of {@link ExpMovingAvg}.
+		 */
+		public ExpMovingAvg alpha(double exponentialDecayValue) {
+			return new ExpMovingAvg(append("alpha", exponentialDecayValue));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$expMovingAvg";
+		}
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AddFieldsOperation.java

@@ -201,4 +201,5 @@ public class AddFieldsOperation extends DocumentEnhancingOperation {
 			AddFieldsOperationBuilder withValueOfExpression(String operation, Object... values);
 		}
 	}
+
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/Aggregation.java

@@ -227,7 +227,7 @@ public class Aggregation {
 
 	/**
 	 * Obtain an {@link AddFieldsOperationBuilder builder} instance to create a new {@link AddFieldsOperation}.
-	 * <p/>
+	 * <br />
 	 * Starting in version 4.2, MongoDB adds a new aggregation pipeline stage {@link AggregationUpdate#set $set} that is
 	 * an alias for {@code $addFields}.
 	 *
@@ -499,6 +499,17 @@ public class Aggregation {
 		return new MatchOperation(criteria);
 	}
 
+	/**
+	 * Creates a new {@link MatchOperation} using the given {@link AggregationExpression}.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @return new instance of {@link MatchOperation}.
+	 * @since 3.3
+	 */
+	public static MatchOperation match(AggregationExpression expression) {
+		return new MatchOperation(expression);
+	}
+
 	/**
 	 * Creates a new {@link GeoNearOperation} instance from the given {@link NearQuery} and the {@code distanceField}. The
 	 * {@code distanceField} defines output field that contains the calculated distance.
@@ -715,7 +726,7 @@ public class Aggregation {
 
 	/**
 	 * Converts this {@link Aggregation} specification to a {@link Document}.
-	 * <p/>
+	 * <br />
 	 * MongoDB requires as of 3.6 cursor-based aggregation. Use {@link #toPipeline(AggregationOperationContext)} to render
 	 * an aggregation pipeline.
 	 *

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AggregationExpression.java

@@ -16,6 +16,7 @@
 package org.springframework.data.mongodb.core.aggregation;
 
 import org.bson.Document;
+import org.springframework.data.mongodb.MongoExpression;
 
 /**
  * An {@link AggregationExpression} can be used with field expressions in aggregation pipeline stages like
@@ -25,7 +26,37 @@ import org.bson.Document;
  * @author Oliver Gierke
  * @author Christoph Strobl
  */
-public interface AggregationExpression {
+public interface AggregationExpression extends MongoExpression {
+
+	/**
+	 * Create an {@link AggregationExpression} out of a given {@link MongoExpression} to ensure the resulting
+	 * {@link MongoExpression#toDocument() Document} is mapped against the {@link AggregationOperationContext}. <br />
+	 * If the given expression is already an {@link AggregationExpression} the very same instance is returned.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @return never {@literal null}.
+	 * @since 3.2
+	 */
+	static AggregationExpression from(MongoExpression expression) {
+
+		if (expression instanceof AggregationExpression) {
+			return AggregationExpression.class.cast(expression);
+		}
+
+		return (context) -> context.getMappedObject(expression.toDocument());
+	}
+
+	/**
+	 * Obtain the as is (unmapped) representation of the {@link AggregationExpression}. Use
+	 * {@link #toDocument(AggregationOperationContext)} with a matching {@link AggregationOperationContext context} to
+	 * engage domain type mapping including field name resolution.
+	 *
+	 * @see org.springframework.data.mongodb.MongoExpression#toDocument()
+	 */
+	@Override
+	default Document toDocument() {
+		return toDocument(Aggregation.DEFAULT_CONTEXT);
+	}
 
 	/**
 	 * Turns the {@link AggregationExpression} into a {@link Document} within the given

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AggregationOptions.java

@@ -56,6 +56,7 @@ public class AggregationOptions {
 	private final Optional<Document> hint;
 	private Duration maxTime = Duration.ZERO;
 	private ResultOptions resultOptions = ResultOptions.READ;
+	private DomainTypeMapping domainTypeMapping = DomainTypeMapping.RELAXED;
 
 	/**
 	 * Creates a new {@link AggregationOptions}.
@@ -261,6 +262,14 @@ public class AggregationOptions {
 		return ResultOptions.SKIP.equals(resultOptions);
 	}
 
+	/**
+	 * @return the domain type mapping strategy do apply. Never {@literal null}.
+	 * @since 3.2
+	 */
+	public DomainTypeMapping getDomainTypeMapping() {
+		return domainTypeMapping;
+	}
+
 	/**
 	 * Returns a new potentially adjusted copy for the given {@code aggregationCommandObject} with the configuration
 	 * applied.
@@ -358,6 +367,7 @@ public class AggregationOptions {
 		private @Nullable Document hint;
 		private @Nullable Duration maxTime;
 		private @Nullable ResultOptions resultOptions;
+		private @Nullable DomainTypeMapping domainTypeMapping;
 
 		/**
 		 * Defines whether to off-load intensive sort-operations to disk.
@@ -475,6 +485,44 @@ public class AggregationOptions {
 			return this;
 		}
 
+		/**
+		 * Apply a strict domain type mapping considering {@link org.springframework.data.mongodb.core.mapping.Field}
+		 * annotations throwing errors for non-existent, but referenced fields.
+		 *
+		 * @return this.
+		 * @since 3.2
+		 */
+		public Builder strictMapping() {
+
+			this.domainTypeMapping = DomainTypeMapping.STRICT;
+			return this;
+		}
+
+		/**
+		 * Apply a relaxed domain type mapping considering {@link org.springframework.data.mongodb.core.mapping.Field}
+		 * annotations using the user provided name if a referenced field does not exist.
+		 *
+		 * @return this.
+		 * @since 3.2
+		 */
+		public Builder relaxedMapping() {
+
+			this.domainTypeMapping = DomainTypeMapping.RELAXED;
+			return this;
+		}
+
+		/**
+		 * Apply no domain type mapping at all taking the pipeline as-is.
+		 *
+		 * @return this.
+		 * @since 3.2
+		 */
+		public Builder noMapping() {
+
+			this.domainTypeMapping = DomainTypeMapping.NONE;
+			return this;
+		}
+
 		/**
 		 * Returns a new {@link AggregationOptions} instance with the given configuration.
 		 *
@@ -489,6 +537,9 @@ public class AggregationOptions {
 			if (resultOptions != null) {
 				options.resultOptions = resultOptions;
 			}
+			if (domainTypeMapping != null) {
+				options.domainTypeMapping = domainTypeMapping;
+			}
 
 			return options;
 		}
@@ -508,4 +559,27 @@ public class AggregationOptions {
 		 */
 		READ;
 	}
+
+	/**
+	 * Aggregation pipeline Domain type mappings supported by the mapping layer.
+	 *
+	 * @since 3.2
+	 */
+	public enum DomainTypeMapping {
+
+		/**
+		 * Mapping throws errors for non-existent, but referenced fields.
+		 */
+		STRICT,
+
+		/**
+		 * Fields that do not exist in the model are treated as-is.
+		 */
+		RELAXED,
+
+		/**
+		 * Do not attempt to map fields against the model and treat the entire pipeline as-is.
+		 */
+		NONE
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AggregationSpELExpression.java

@@ -24,15 +24,15 @@ import org.springframework.util.Assert;
  * expression</a>. <br />
  * <br />
  * <strong>Samples:</strong> <br />
- * <code>
  * <pre>
+ * <code>
  * // { $and: [ { $gt: [ "$qty", 100 ] }, { $lt: [ "$qty", 250 ] } ] }
  * expressionOf("qty > 100 && qty < 250);
  *
  * // { $cond : { if : { $gte : [ "$a", 42 ]}, then : "answer", else : "no-answer" } }
  * expressionOf("cond(a >= 42, 'answer', 'no-answer')");
- * </pre>
  * </code>
+ * </pre>
  *
  * @author Christoph Strobl
  * @author Mark Paluch

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AggregationUpdate.java

@@ -71,8 +71,7 @@ import org.springframework.util.Assert;
  *
  * @author Christoph Strobl
  * @author Mark Paluch
- * @see <a href=
- *      "https://docs.mongodb.com/manual/reference/method/db.collection.update/#update-with-aggregation-pipeline">MongoDB
+ * @see <a href="https://docs.mongodb.com/manual/reference/method/db.collection.update/#update-with-aggregation-pipeline">MongoDB
  *      Reference Documentation</a>
  * @since 3.0
  */

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/BucketAutoOperation.java

@@ -28,8 +28,7 @@ import org.springframework.util.Assert;
  * We recommend to use the static factory method {@link Aggregation#bucketAuto(String, int)} instead of creating
  * instances of this class directly.
  *
- * @see <a href=
- *      "https://docs.mongodb.org/manual/reference/aggregation/bucketAuto/">https://docs.mongodb.org/manual/reference/aggregation/bucketAuto/</a>
+ * @see <a href="https://docs.mongodb.org/manual/reference/aggregation/bucketAuto/">https://docs.mongodb.org/manual/reference/aggregation/bucketAuto/</a>
  * @see BucketOperationSupport
  * @author Mark Paluch
  * @author Christoph Strobl
@@ -248,8 +247,7 @@ public class BucketAutoOperation extends BucketOperationSupport<BucketAutoOperat
 	/**
 	 * Supported MongoDB granularities.
 	 *
-	 * @see <a
-	 *      href="https://docs.mongodb.com/manual/reference/operator/aggregation/bucketAuto/#granularity>https://docs.mongodb.com/manual/reference/operator/aggregation/bucketAuto/#granularity</a>
+	 * @see <a href="https://docs.mongodb.com/manual/reference/operator/aggregation/bucketAuto/#granularity">https://docs.mongodb.com/manual/reference/operator/aggregation/bucketAuto/#granularity</a>
 	 * @author Mark Paluch
 	 */
 	public enum Granularities implements Granularity {

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/BucketOperation.java

@@ -31,8 +31,7 @@ import org.springframework.util.Assert;
  * We recommend to use the static factory method {@link Aggregation#bucket(String)} instead of creating instances of
  * this class directly.
  *
- * @see <a href=
- *      "https://docs.mongodb.org/manual/reference/aggregation/bucket/">https://docs.mongodb.org/manual/reference/aggregation/bucket/</a>
+ * @see <a href="https://docs.mongodb.org/manual/reference/aggregation/bucket/">https://docs.mongodb.org/manual/reference/aggregation/bucket/</a>
  * @see BucketOperationSupport
  * @author Mark Paluch
  * @since 1.10

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ConditionalOperators.java

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.core.aggregation;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 
@@ -235,7 +236,7 @@ public class ConditionalOperators {
 	 *
 	 * @author Mark Paluch
 	 * @see <a href=
-	 * "https://docs.mongodb.com/manual/reference/operator/aggregation/ifNull/">https://docs.mongodb.com/manual/reference/operator/aggregation/ifNull/</a>
+	 *      "https://docs.mongodb.com/manual/reference/operator/aggregation/ifNull/">https://docs.mongodb.com/manual/reference/operator/aggregation/ifNull/</a>
 	 */
 	public static class IfNull implements AggregationExpression {
 
@@ -251,7 +252,8 @@ public class ConditionalOperators {
 		/**
 		 * Creates new {@link IfNull}.
 		 *
-		 * @param fieldReference the field to check for a {@literal null} value, field reference must not be {@literal null}.
+		 * @param fieldReference the field to check for a {@literal null} value, field reference must not be
+		 *          {@literal null}.
 		 * @return never {@literal null}.
 		 */
 		public static ThenBuilder ifNull(String fieldReference) {
@@ -264,7 +266,7 @@ public class ConditionalOperators {
 		 * Creates new {@link IfNull}.
 		 *
 		 * @param expression the expression to check for a {@literal null} value, field reference must not be
-		 * {@literal null}.
+		 *          {@literal null}.
 		 * @return never {@literal null}.
 		 */
 		public static ThenBuilder ifNull(AggregationExpression expression) {
@@ -282,19 +284,29 @@ public class ConditionalOperators {
 
 			List<Object> list = new ArrayList<Object>();
 
-			if (condition instanceof Field) {
-				list.add(context.getReference((Field) condition).toString());
-			} else if (condition instanceof AggregationExpression) {
-				list.add(((AggregationExpression) condition).toDocument(context));
+			if (condition instanceof Collection) {
+				for (Object val : ((Collection) this.condition)) {
+					list.add(mapCondition(val, context));
+				}
 			} else {
-				list.add(condition);
+				list.add(mapCondition(condition, context));
 			}
 
 			list.add(resolve(value, context));
-
 			return new Document("$ifNull", list);
 		}
 
+		private Object mapCondition(Object condition, AggregationOperationContext context) {
+
+			if (condition instanceof Field) {
+				return context.getReference((Field) condition).toString();
+			} else if (condition instanceof AggregationExpression) {
+				return ((AggregationExpression) condition).toDocument(context);
+			} else {
+				return condition;
+			}
+		}
+
 		private Object resolve(Object value, AggregationOperationContext context) {
 
 			if (value instanceof Field) {
@@ -315,28 +327,48 @@ public class ConditionalOperators {
 
 			/**
 			 * @param fieldReference the field to check for a {@literal null} value, field reference must not be
-			 * {@literal null}.
+			 *          {@literal null}.
 			 * @return the {@link ThenBuilder}
 			 */
 			ThenBuilder ifNull(String fieldReference);
 
 			/**
 			 * @param expression the expression to check for a {@literal null} value, field name must not be {@literal null}
-			 * or empty.
-			 * @return the {@link ThenBuilder}
+			 *          or empty.
+			 * @return the {@link ThenBuilder}.
 			 */
 			ThenBuilder ifNull(AggregationExpression expression);
 		}
 
+		/**
+		 * @author Christoph Strobl
+		 * @since 3.3
+		 */
+		public interface OrBuilder {
+
+			/**
+			 * @param fieldReference the field to check for a {@literal null} value, field reference must not be
+			 *          {@literal null}.
+			 * @return the {@link ThenBuilder}
+			 */
+			ThenBuilder orIfNull(String fieldReference);
+
+			/**
+			 * @param expression the expression to check for a {@literal null} value,
+			 * @return the {@link ThenBuilder}.
+			 */
+			ThenBuilder orIfNull(AggregationExpression expression);
+		}
+
 		/**
 		 * @author Mark Paluch
 		 */
-		public interface ThenBuilder {
+		public interface ThenBuilder extends OrBuilder {
 
 			/**
 			 * @param value the value to be used if the {@code $ifNull} condition evaluates {@literal true}. Can be a
-			 * {@link Document}, a value that is supported by MongoDB or a value that can be converted to a MongoDB
-			 * representation but must not be {@literal null}.
+			 *          {@link Document}, a value that is supported by MongoDB or a value that can be converted to a MongoDB
+			 *          representation but must not be {@literal null}.
 			 * @return new instance of {@link IfNull}.
 			 */
 			IfNull then(Object value);
@@ -361,9 +393,10 @@ public class ConditionalOperators {
 		 */
 		static final class IfNullOperatorBuilder implements IfNullBuilder, ThenBuilder {
 
-			private @Nullable Object condition;
+			private @Nullable List<Object> conditions;
 
 			private IfNullOperatorBuilder() {
+				conditions = new ArrayList<>();
 			}
 
 			/**
@@ -381,7 +414,7 @@ public class ConditionalOperators {
 			public ThenBuilder ifNull(String fieldReference) {
 
 				Assert.hasText(fieldReference, "FieldReference name must not be null or empty!");
-				this.condition = Fields.field(fieldReference);
+				this.conditions.add(Fields.field(fieldReference));
 				return this;
 			}
 
@@ -392,15 +425,25 @@ public class ConditionalOperators {
 			public ThenBuilder ifNull(AggregationExpression expression) {
 
 				Assert.notNull(expression, "AggregationExpression name must not be null or empty!");
-				this.condition = expression;
+				this.conditions.add(expression);
 				return this;
 			}
 
+			@Override
+			public ThenBuilder orIfNull(String fieldReference) {
+				return ifNull(fieldReference);
+			}
+
+			@Override
+			public ThenBuilder orIfNull(AggregationExpression expression) {
+				return ifNull(expression);
+			}
+
 			/* (non-Javadoc)
 			 * @see org.springframework.data.mongodb.core.aggregation.ConditionalOperators.IfNull.ThenBuilder#then(java.lang.Object)
 			 */
 			public IfNull then(Object value) {
-				return new IfNull(condition, value);
+				return new IfNull(conditions, value);
 			}
 
 			/* (non-Javadoc)
@@ -409,7 +452,7 @@ public class ConditionalOperators {
 			public IfNull thenValueOf(String fieldReference) {
 
 				Assert.notNull(fieldReference, "FieldReference must not be null!");
-				return new IfNull(condition, Fields.field(fieldReference));
+				return new IfNull(conditions, Fields.field(fieldReference));
 			}
 
 			/* (non-Javadoc)
@@ -418,7 +461,7 @@ public class ConditionalOperators {
 			public IfNull thenValueOf(AggregationExpression expression) {
 
 				Assert.notNull(expression, "Expression must not be null!");
-				return new IfNull(condition, expression);
+				return new IfNull(conditions, expression);
 			}
 		}
 	}
@@ -458,7 +501,7 @@ public class ConditionalOperators {
 		public static Switch switchCases(List<CaseOperator> conditions) {
 
 			Assert.notNull(conditions, "Conditions must not be null!");
-			return new Switch(Collections.<String, Object>singletonMap("branches", new ArrayList<CaseOperator>(conditions)));
+			return new Switch(Collections.<String, Object> singletonMap("branches", new ArrayList<CaseOperator>(conditions)));
 		}
 
 		/**
@@ -545,7 +588,7 @@ public class ConditionalOperators {
 	 * @author Mark Paluch
 	 * @author Christoph Strobl
 	 * @see <a href=
-	 * "https://docs.mongodb.com/manual/reference/operator/aggregation/cond/">https://docs.mongodb.com/manual/reference/operator/aggregation/cond/</a>
+	 *      "https://docs.mongodb.com/manual/reference/operator/aggregation/cond/">https://docs.mongodb.com/manual/reference/operator/aggregation/cond/</a>
 	 */
 	public static class Cond implements AggregationExpression {
 
@@ -806,8 +849,8 @@ public class ConditionalOperators {
 
 			/**
 			 * @param value the value to be used if the condition evaluates {@literal true}. Can be a {@link Document}, a
-			 * value that is supported by MongoDB or a value that can be converted to a MongoDB representation but
-			 * must not be {@literal null}.
+			 *          value that is supported by MongoDB or a value that can be converted to a MongoDB representation but
+			 *          must not be {@literal null}.
 			 * @return the {@link OtherwiseBuilder}
 			 */
 			OtherwiseBuilder then(Object value);
@@ -832,8 +875,8 @@ public class ConditionalOperators {
 
 			/**
 			 * @param value the value to be used if the condition evaluates {@literal false}. Can be a {@link Document}, a
-			 * value that is supported by MongoDB or a value that can be converted to a MongoDB representation but
-			 * must not be {@literal null}.
+			 *          value that is supported by MongoDB or a value that can be converted to a MongoDB representation but
+			 *          must not be {@literal null}.
 			 * @return the {@link Cond}
 			 */
 			Cond otherwise(Object value);
@@ -861,8 +904,7 @@ public class ConditionalOperators {
 			private @Nullable Object condition;
 			private @Nullable Object thenValue;
 
-			private ConditionalExpressionBuilder() {
-			}
+			private ConditionalExpressionBuilder() {}
 
 			/**
 			 * Creates a new builder for {@link Cond}.

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ConvertOperators.java

@@ -231,6 +231,17 @@ public class ConvertOperators {
 			return ToString.toString(valueObject());
 		}
 
+		/**
+		 * {@link AggregationExpression} for {@code $degreesToRadians} that converts an input value measured in degrees to
+		 * radians.
+		 *
+		 * @return new instance of {@link DegreesToRadians}.
+		 * @since 3.3
+		 */
+		public DegreesToRadians convertDegreesToRadians() {
+			return DegreesToRadians.degreesToRadians(valueObject());
+		}
+
 		private Convert createConvert() {
 			return usesFieldRef() ? Convert.convertValueOf(fieldReference) : Convert.convertValueOf(expression);
 		}
@@ -317,9 +328,9 @@ public class ConvertOperators {
 		 * <dt>1</dt>
 		 * <dd>double</dd>
 		 * <dt>2</dt>
-		 * <dd>string</li>
+		 * <dd>string</dd>
 		 * <dt>7</dt>
-		 * <dd>objectId</li>
+		 * <dd>objectId</dd>
 		 * <dt>8</dt>
 		 * <dd>bool</dd>
 		 * <dt>9</dt>
@@ -692,4 +703,52 @@ public class ConvertOperators {
 			return "$toString";
 		}
 	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $degreesToRadians} that converts an input value measured in degrees to radians.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class DegreesToRadians extends AbstractAggregationExpression {
+
+		private DegreesToRadians(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Create a new instance of {@link DegreesToRadians} that converts the value of the given field, measured in degrees, to radians.
+		 *
+		 * @param fieldName must not be {@literal null}.
+		 * @return new instance of {@link DegreesToRadians}.
+		 */
+		public static DegreesToRadians degreesToRadiansOf(String fieldName) {
+			return degreesToRadians(Fields.field(fieldName));
+		}
+
+		/**
+		 * Create a new instance of {@link DegreesToRadians} that converts the result of the given {@link AggregationExpression expression}, measured in degrees, to radians.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link DegreesToRadians}.
+		 */
+		public static DegreesToRadians degreesToRadiansOf(AggregationExpression expression) {
+			return degreesToRadians(expression);
+		}
+
+		/**
+		 * Create a new instance of {@link DegreesToRadians} that converts the given value, measured in degrees, to radians.
+		 *
+		 * @param value must not be {@literal null}.
+		 * @return new instance of {@link DegreesToRadians}.
+		 */
+		public static DegreesToRadians degreesToRadians(Object value) {
+			return new DegreesToRadians(value);
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$degreesToRadians";
+		}
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/CountOperation.java

@@ -24,8 +24,7 @@ import org.springframework.util.Assert;
  * We recommend to use the static factory method {@link Aggregation#count()} instead of creating instances of this class
  * directly.
  *
- * @see <a href=
- *      "https://docs.mongodb.com/manual/reference/operator/aggregation/count/#pipe._S_count">https://docs.mongodb.com/manual/reference/operator/aggregation/count/</a>
+ * @see <a href="https://docs.mongodb.com/manual/reference/operator/aggregation/count/#pipe._S_count">https://docs.mongodb.com/manual/reference/operator/aggregation/count/</a>
  * @author Mark Paluch
  * @since 1.10
  */

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/DateOperators.java

@@ -15,9 +15,16 @@
  */
 package org.springframework.data.mongodb.core.aggregation;
 
+import java.time.ZoneId;
+import java.time.ZoneOffset;
+import java.time.temporal.ChronoUnit;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.LinkedHashMap;
+import java.util.Locale;
 import java.util.Map;
+import java.util.TimeZone;
+import java.util.concurrent.TimeUnit;
 
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
@@ -45,6 +52,19 @@ public class DateOperators {
 		return new DateOperatorFactory(fieldReference);
 	}
 
+	/**
+	 * Take the date referenced by given {@literal fieldReference}.
+	 *
+	 * @param fieldReference must not be {@literal null}.
+	 * @return new instance of {@link DateOperatorFactory}.
+	 * @since 3.3
+	 */
+	public static DateOperatorFactory zonedDateOf(String fieldReference, Timezone timezone) {
+
+		Assert.notNull(fieldReference, "FieldReference must not be null!");
+		return new DateOperatorFactory(fieldReference).withTimezone(timezone);
+	}
+
 	/**
 	 * Take the date resulting from the given {@link AggregationExpression}.
 	 *
@@ -57,9 +77,22 @@ public class DateOperators {
 		return new DateOperatorFactory(expression);
 	}
 
+	/**
+	 * Take the date resulting from the given {@link AggregationExpression}.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @return new instance of {@link DateOperatorFactory}.
+	 * @since 3.3
+	 */
+	public static DateOperatorFactory zonedDateOf(AggregationExpression expression, Timezone timezone) {
+
+		Assert.notNull(expression, "Expression must not be null!");
+		return new DateOperatorFactory(expression).withTimezone(timezone);
+	}
+
 	/**
 	 * Take the given value as date.
-	 * <p/>
+	 * <br />
 	 * This can be one of:
 	 * <ul>
 	 * <li>{@link java.util.Date}</li>
@@ -109,7 +142,7 @@ public class DateOperators {
 	 * Timezone represents a MongoDB timezone abstraction which can be represented with a timezone ID or offset as a
 	 * {@link String}. Also accepts a {@link AggregationExpression} or {@link Field} that resolves to a {@link String} of
 	 * either Olson Timezone Identifier or a UTC Offset.<br />
-	 * <table valign="top">
+	 * <table>
 	 * <tr>
 	 * <th>Format</th>
 	 * <th>Example</th>
@@ -130,6 +163,7 @@ public class DateOperators {
 	 * <strong>NOTE: </strong>Support for timezones in aggregations Requires MongoDB 3.6 or later.
 	 *
 	 * @author Christoph Strobl
+	 * @author Mark Paluch
 	 * @since 2.1
 	 */
 	public static class Timezone {
@@ -156,7 +190,7 @@ public class DateOperators {
 		 * representing an Olson Timezone Identifier or UTC Offset.
 		 *
 		 * @param value the plain timezone {@link String}, a {@link Field} holding the timezone or an
-		 *          {@link AggregationExpression} resulting in the timezone.
+		 * {@link AggregationExpression} resulting in the timezone.
 		 * @return new instance of {@link Timezone}.
 		 */
 		public static Timezone valueOf(Object value) {
@@ -165,6 +199,61 @@ public class DateOperators {
 			return new Timezone(value);
 		}
 
+		/**
+		 * Create a {@link Timezone} for the given {@link TimeZone} rendering the offset as UTC offset.
+		 *
+		 * @param timeZone {@link TimeZone} rendering the offset as UTC offset.
+		 * @return new instance of {@link Timezone}.
+		 * @since 3.3
+		 */
+		public static Timezone fromOffset(TimeZone timeZone) {
+
+			Assert.notNull(timeZone, "TimeZone must not be null!");
+
+			return fromOffset(
+					ZoneOffset.ofTotalSeconds(Math.toIntExact(TimeUnit.MILLISECONDS.toSeconds(timeZone.getRawOffset()))));
+		}
+
+		/**
+		 * Create a {@link Timezone} for the given {@link ZoneOffset} rendering the offset as UTC offset.
+		 *
+		 * @param offset {@link ZoneOffset} rendering the offset as UTC offset.
+		 * @return new instance of {@link Timezone}.
+		 * @since 3.3
+		 */
+		public static Timezone fromOffset(ZoneOffset offset) {
+
+			Assert.notNull(offset, "ZoneOffset must not be null!");
+			return new Timezone(offset.toString());
+		}
+
+		/**
+		 * Create a {@link Timezone} for the given {@link TimeZone} rendering the offset as UTC offset.
+		 *
+		 * @param timeZone {@link Timezone} rendering the offset as zone identifier.
+		 * @return new instance of {@link Timezone}.
+		 * @since 3.3
+		 */
+		public static Timezone fromZone(TimeZone timeZone) {
+
+			Assert.notNull(timeZone, "TimeZone must not be null!");
+
+			return valueOf(timeZone.getID());
+		}
+
+		/**
+		 * Create a {@link Timezone} for the given {@link java.time.ZoneId} rendering the offset as UTC offset.
+		 *
+		 * @param zoneId {@link ZoneId} rendering the offset as zone identifier.
+		 * @return new instance of {@link Timezone}.
+		 * @since 3.3
+		 */
+		public static Timezone fromZone(ZoneId zoneId) {
+
+			Assert.notNull(zoneId, "ZoneId must not be null!");
+			return new Timezone(zoneId.toString());
+		}
+
 		/**
 		 * Create a {@link Timezone} for the {@link Field} reference holding the Olson Timezone Identifier or UTC Offset.
 		 *
@@ -185,6 +274,11 @@ public class DateOperators {
 		public static Timezone ofExpression(AggregationExpression expression) {
 			return valueOf(expression);
 		}
+
+		@Nullable
+		Object getValue() {
+			return value;
+		}
 	}
 
 	/**
@@ -240,7 +334,7 @@ public class DateOperators {
 
 		/**
 		 * Creates new {@link DateOperatorFactory} for given {@code value} that resolves to a Date.
-		 * <p/>
+		 * <br />
 		 * <ul>
 		 * <li>{@link java.util.Date}</li>
 		 * <li>{@link java.util.Calendar}</li>
@@ -274,6 +368,89 @@ public class DateOperators {
 			return new DateOperatorFactory(fieldReference, expression, dateValue, timezone);
 		}
 
+		/**
+		 * Creates new {@link AggregationExpression} that adds the value of the given {@link AggregationExpression
+		 * expression} (in {@literal units}).
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateAdd addValueOf(AggregationExpression expression, String unit) {
+			return applyTimezone(DateAdd.addValueOf(expression, unit).toDate(dateReference()), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that adds the value of the given {@link AggregationExpression
+		 * expression} (in {@literal units}).
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateAdd addValueOf(AggregationExpression expression, TemporalUnit unit) {
+
+			Assert.notNull(unit, "TemporalUnit must not be null");
+			return applyTimezone(DateAdd.addValueOf(expression, unit.name().toLowerCase(Locale.ROOT)).toDate(dateReference()),
+					timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that adds the value stored at the given {@literal field} (in
+		 * {@literal units}).
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateAdd addValueOf(String fieldReference, String unit) {
+			return applyTimezone(DateAdd.addValueOf(fieldReference, unit).toDate(dateReference()), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that adds the value stored at the given {@literal field} (in
+		 * {@literal units}).
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateAdd addValueOf(String fieldReference, TemporalUnit unit) {
+
+			Assert.notNull(unit, "TemporalUnit must not be null");
+
+			return applyTimezone(
+					DateAdd.addValueOf(fieldReference, unit.name().toLowerCase(Locale.ROOT)).toDate(dateReference()), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that adds the given value (in {@literal units}).
+		 *
+		 * @param value must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return
+		 * @since 3.3 new instance of {@link DateAdd}.
+		 */
+		public DateAdd add(Object value, String unit) {
+			return applyTimezone(DateAdd.addValue(value, unit).toDate(dateReference()), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that adds the given value (in {@literal units}).
+		 *
+		 * @param value must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return
+		 * @since 3.3 new instance of {@link DateAdd}.
+		 */
+		public DateAdd add(Object value, TemporalUnit unit) {
+
+			Assert.notNull(unit, "TemporalUnit must not be null");
+
+			return applyTimezone(DateAdd.addValue(value, unit.name().toLowerCase(Locale.ROOT)).toDate(dateReference()),
+					timezone);
+		}
+
 		/**
 		 * Creates new {@link AggregationExpression} that returns the day of the year for a date as a number between 1 and
 		 * 366.
@@ -304,6 +481,90 @@ public class DateOperators {
 			return applyTimezone(DayOfWeek.dayOfWeek(dateReference()), timezone);
 		}
 
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the difference (in {@literal units}) to the date
+		 * computed by the given {@link AggregationExpression expression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateDiff diffValueOf(AggregationExpression expression, String unit) {
+			return applyTimezone(DateDiff.diffValueOf(expression, unit).toDate(dateReference()), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the difference (in {@literal units}) to the date
+		 * computed by the given {@link AggregationExpression expression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateDiff diffValueOf(AggregationExpression expression, TemporalUnit unit) {
+
+			Assert.notNull(unit, "TemporalUnit must not be null");
+
+			return applyTimezone(
+					DateDiff.diffValueOf(expression, unit.name().toLowerCase(Locale.ROOT)).toDate(dateReference()), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the difference (in {@literal units}) to the date stored
+		 * at the given {@literal field}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateDiff diffValueOf(String fieldReference, String unit) {
+			return applyTimezone(DateDiff.diffValueOf(fieldReference, unit).toDate(dateReference()), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the difference (in {@literal units}) to the date stored
+		 * at the given {@literal field}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateDiff diffValueOf(String fieldReference, TemporalUnit unit) {
+
+			Assert.notNull(unit, "TemporalUnit must not be null");
+
+			return applyTimezone(
+					DateDiff.diffValueOf(fieldReference, unit.name().toLowerCase(Locale.ROOT)).toDate(dateReference()), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the difference (in {@literal units}) to the date given
+		 * {@literal value}.
+		 *
+		 * @param value anything the resolves to a valid date. Must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateDiff diff(Object value, String unit) {
+			return applyTimezone(DateDiff.diffValue(value, unit).toDate(dateReference()), timezone);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that calculates the difference (in {@literal units}) to the date given
+		 * {@literal value}.
+		 *
+		 * @param value anything the resolves to a valid date. Must not be {@literal null}.
+		 * @param unit the unit of measure. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}. @since 3.3
+		 */
+		public DateDiff diff(Object value, TemporalUnit unit) {
+
+			Assert.notNull(unit, "TemporalUnit must not be null");
+
+			return applyTimezone(DateDiff.diffValue(value, unit.name().toLowerCase(Locale.ROOT)).toDate(dateReference()),
+					timezone);
+		}
+
 		/**
 		 * Creates new {@link AggregationExpression} that returns the year portion of a date.
 		 *
@@ -1480,7 +1741,6 @@ public class DateOperators {
 				} else {
 					clone.put("timezone", ((Timezone) value).value);
 				}
-
 			} else {
 				clone.put(key, value);
 			}
@@ -1911,7 +2171,7 @@ public class DateOperators {
 	 * @author Matt Morrissette
 	 * @author Christoph Strobl
 	 * @see <a href=
-	 *      "https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromParts/">https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromParts/</a>
+	 * "https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromParts/">https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromParts/</a>
 	 * @since 2.1
 	 */
 	public static class DateFromParts extends TimezonedDateAggregationExpression implements DateParts<DateFromParts> {
@@ -2086,7 +2346,7 @@ public class DateOperators {
 	 * @author Matt Morrissette
 	 * @author Christoph Strobl
 	 * @see <a href=
-	 *      "https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromParts/">https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromParts/</a>
+	 * "https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromParts/">https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromParts/</a>
 	 * @since 2.1
 	 */
 	public static class IsoDateFromParts extends TimezonedDateAggregationExpression
@@ -2262,7 +2522,7 @@ public class DateOperators {
 	 * @author Matt Morrissette
 	 * @author Christoph Strobl
 	 * @see <a href=
-	 *      "https://docs.mongodb.com/manual/reference/operator/aggregation/dateToParts/">https://docs.mongodb.com/manual/reference/operator/aggregation/dateToParts/</a>
+	 * "https://docs.mongodb.com/manual/reference/operator/aggregation/dateToParts/">https://docs.mongodb.com/manual/reference/operator/aggregation/dateToParts/</a>
 	 * @since 2.1
 	 */
 	public static class DateToParts extends TimezonedDateAggregationExpression {
@@ -2343,7 +2603,7 @@ public class DateOperators {
 	 * @author Matt Morrissette
 	 * @author Christoph Strobl
 	 * @see <a href=
-	 *      "https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromString/">https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromString/</a>
+	 * "https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromString/">https://docs.mongodb.com/manual/reference/operator/aggregation/dateFromString/</a>
 	 * @since 2.1
 	 */
 	public static class DateFromString extends TimezonedDateAggregationExpression {
@@ -2418,6 +2678,290 @@ public class DateOperators {
 		}
 	}
 
+	/**
+	 * {@link AggregationExpression} for {@code $dateAdd}.<br />
+	 * <strong>NOTE:</strong> Requires MongoDB 5.0 or later.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class DateAdd extends TimezonedDateAggregationExpression {
+
+		private DateAdd(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Add the number of {@literal units} of the result of the given {@link AggregationExpression expression} to a
+		 * {@link #toDate(Object) start date}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @param unit must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public static DateAdd addValueOf(AggregationExpression expression, String unit) {
+			return addValue(expression, unit);
+		}
+
+		/**
+		 * Add the number of {@literal units} from a {@literal field} to a {@link #toDate(Object) start date}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @param unit must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public static DateAdd addValueOf(String fieldReference, String unit) {
+			return addValue(Fields.field(fieldReference), unit);
+		}
+
+		/**
+		 * Add the number of {@literal units} to a {@link #toDate(Object) start date}.
+		 *
+		 * @param value must not be {@literal null}.
+		 * @param unit must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public static DateAdd addValue(Object value, String unit) {
+
+			Map<String, Object> args = new HashMap<>();
+			args.put("unit", unit);
+			args.put("amount", value);
+			return new DateAdd(args);
+		}
+
+		/**
+		 * Define the start date, in UTC, for the addition operation.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public DateAdd toDateOf(AggregationExpression expression) {
+			return toDate(expression);
+		}
+
+		/**
+		 * Define the start date, in UTC, for the addition operation.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public DateAdd toDateOf(String fieldReference) {
+			return toDate(Fields.field(fieldReference));
+		}
+
+		/**
+		 * Define the start date, in UTC, for the addition operation.
+		 *
+		 * @param dateExpression anything that evaluates to a valid date. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public DateAdd toDate(Object dateExpression) {
+			return new DateAdd(append("startDate", dateExpression));
+		}
+
+		/**
+		 * Optionally set the {@link Timezone} to use. If not specified {@literal UTC} is used.
+		 *
+		 * @param timezone must not be {@literal null}. Consider {@link Timezone#none()} instead.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public DateAdd withTimezone(Timezone timezone) {
+			return new DateAdd(appendTimezone(argumentMap(), timezone));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$dateAdd";
+		}
+	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $dateDiff}.<br />
+	 * <strong>NOTE:</strong> Requires MongoDB 5.0 or later.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class DateDiff extends TimezonedDateAggregationExpression {
+
+		private DateDiff(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Add the number of {@literal units} of the result of the given {@link AggregationExpression expression} to a
+		 * {@link #toDate(Object) start date}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @param unit must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public static DateDiff diffValueOf(AggregationExpression expression, String unit) {
+			return diffValue(expression, unit);
+		}
+
+		/**
+		 * Add the number of {@literal units} from a {@literal field} to a {@link #toDate(Object) start date}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @param unit must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public static DateDiff diffValueOf(String fieldReference, String unit) {
+			return diffValue(Fields.field(fieldReference), unit);
+		}
+
+		/**
+		 * Add the number of {@literal units} to a {@link #toDate(Object) start date}.
+		 *
+		 * @param value must not be {@literal null}.
+		 * @param unit must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public static DateDiff diffValue(Object value, String unit) {
+
+			Map<String, Object> args = new HashMap<>();
+			args.put("unit", unit);
+			args.put("endDate", value);
+			return new DateDiff(args);
+		}
+
+		/**
+		 * Define the start date, in UTC, for the addition operation.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public DateDiff toDateOf(AggregationExpression expression) {
+			return toDate(expression);
+		}
+
+		/**
+		 * Define the start date, in UTC, for the addition operation.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public DateDiff toDateOf(String fieldReference) {
+			return toDate(Fields.field(fieldReference));
+		}
+
+		/**
+		 * Define the start date, in UTC, for the addition operation.
+		 *
+		 * @param dateExpression anything that evaluates to a valid date. Must not be {@literal null}.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public DateDiff toDate(Object dateExpression) {
+			return new DateDiff(append("startDate", dateExpression));
+		}
+
+		/**
+		 * Optionally set the {@link Timezone} to use. If not specified {@literal UTC} is used.
+		 *
+		 * @param timezone must not be {@literal null}. Consider {@link Timezone#none()} instead.
+		 * @return new instance of {@link DateAdd}.
+		 */
+		public DateDiff withTimezone(Timezone timezone) {
+			return new DateDiff(appendTimezone(argumentMap(), timezone));
+		}
+
+		/**
+		 * Set the start day of the week if the unit if measure is set to {@literal week}. Uses {@literal Sunday} by
+		 * default.
+		 *
+		 * @param day must not be {@literal null}.
+		 * @return new instance of {@link DateDiff}.
+		 */
+		public DateDiff startOfWeek(Object day) {
+			return new DateDiff(append("startOfWeek", day));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$dateDiff";
+		}
+	}
+
+	/**
+	 * Interface defining a temporal unit for date operators.
+	 *
+	 * @author Mark Paluch
+	 * @since 3.3
+	 */
+	public interface TemporalUnit {
+
+		String name();
+
+		/**
+		 * Converts the given time unit into a {@link TemporalUnit}. Supported units are: days, hours, minutes, seconds, and
+		 * milliseconds.
+		 *
+		 * @param timeUnit the time unit to convert, must not be {@literal null}.
+		 * @return
+		 * @throws IllegalArgumentException if the {@link TimeUnit} is {@literal null} or not supported for conversion.
+		 */
+		static TemporalUnit from(TimeUnit timeUnit) {
+
+			Assert.notNull(timeUnit, "TimeUnit must not be null");
+
+			switch (timeUnit) {
+				case DAYS:
+					return TemporalUnits.DAY;
+				case HOURS:
+					return TemporalUnits.HOUR;
+				case MINUTES:
+					return TemporalUnits.MINUTE;
+				case SECONDS:
+					return TemporalUnits.SECOND;
+				case MILLISECONDS:
+					return TemporalUnits.MILLISECOND;
+			}
+
+			throw new IllegalArgumentException(String.format("Cannot create TemporalUnit from %s", timeUnit));
+		}
+
+		/**
+		 * Converts the given chrono unit into a {@link TemporalUnit}. Supported units are: years, weeks, months, days,
+		 * hours, minutes, seconds, and millis.
+		 *
+		 * @param chronoUnit the chrono unit to convert, must not be {@literal null}.
+		 * @return
+		 * @throws IllegalArgumentException if the {@link TimeUnit} is {@literal null} or not supported for conversion.
+		 */
+		static TemporalUnit from(ChronoUnit chronoUnit) {
+
+			switch (chronoUnit) {
+				case YEARS:
+					return TemporalUnits.YEAR;
+				case WEEKS:
+					return TemporalUnits.WEEK;
+				case MONTHS:
+					return TemporalUnits.MONTH;
+				case DAYS:
+					return TemporalUnits.DAY;
+				case HOURS:
+					return TemporalUnits.HOUR;
+				case MINUTES:
+					return TemporalUnits.MINUTE;
+				case SECONDS:
+					return TemporalUnits.SECOND;
+				case MILLIS:
+					return TemporalUnits.MILLISECOND;
+			}
+
+			throw new IllegalArgumentException(String.format("Cannot create TemporalUnit from %s", chronoUnit));
+		}
+	}
+
+	/**
+	 * Supported temporal units.
+	 */
+	enum TemporalUnits implements TemporalUnit {
+		YEAR, QUARTER, WEEK, MONTH, DAY, HOUR, MINUTE, SECOND, MILLISECOND
+
+	}
+
 	@SuppressWarnings("unchecked")
 	private static <T extends TimezonedDateAggregationExpression> T applyTimezone(T instance, Timezone timezone) {
 		return !ObjectUtils.nullSafeEquals(Timezone.none(), timezone) && !instance.hasTimezone()

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/DocumentOperators.java

@@ -0,0 +1,222 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.core.aggregation;
+
+import java.util.Collections;
+
+import org.bson.Document;
+
+/**
+ * Gateway to {@literal document expressions} such as {@literal $rank, $documentNumber, etc.}
+ *
+ * @author Christoph Strobl
+ * @since 3.3
+ */
+public class DocumentOperators {
+
+	/**
+	 * Obtain the document position (including gaps) relative to others (rank).
+	 *
+	 * @return new instance of {@link Rank}.
+	 * @since 3.3
+	 */
+	public static Rank rank() {
+		return new Rank();
+	}
+
+	/**
+	 * Obtain the document position (without gaps) relative to others (rank).
+	 *
+	 * @return new instance of {@link DenseRank}.
+	 * @since 3.3
+	 */
+	public static DenseRank denseRank() {
+		return new DenseRank();
+	}
+
+	/**
+	 * Take the field referenced by given {@literal fieldReference}.
+	 *
+	 * @param fieldReference must not be {@literal null}.
+	 * @return new instance of {@link DocumentOperatorsFactory}.
+	 */
+	public static DocumentOperatorsFactory valueOf(String fieldReference) {
+		return new DocumentOperatorsFactory(fieldReference);
+	}
+
+	/**
+	 * Take the value resulting from the given {@link AggregationExpression}.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @return new instance of {@link DocumentOperatorsFactory}.
+	 */
+	public static DocumentOperatorsFactory valueOf(AggregationExpression expression) {
+		return new DocumentOperatorsFactory(expression);
+	}
+
+	/**
+	 * Obtain the current document position.
+	 *
+	 * @return new instance of {@link DocumentNumber}.
+	 * @since 3.3
+	 */
+	public static DocumentNumber documentNumber() {
+		return new DocumentNumber();
+	}
+
+	/**
+	 * @author Christoph Strobl
+	 */
+	public static class DocumentOperatorsFactory {
+
+		private final Object target;
+
+		public DocumentOperatorsFactory(Object target) {
+			this.target = target;
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that applies the expression to a document at specified position
+		 * relative to the current document.
+		 *
+		 * @param by the value to add to the current position.
+		 * @return new instance of {@link Shift}.
+		 */
+		public Shift shift(int by) {
+
+			Shift shift = usesExpression() ? Shift.shift((AggregationExpression) target) : Shift.shift(target.toString());
+			return shift.by(by);
+		}
+
+		private boolean usesExpression() {
+			return target instanceof AggregationExpression;
+		}
+	}
+
+	/**
+	 * {@link Rank} resolves the current document position (the rank) relative to other documents. If multiple documents
+	 * occupy the same rank, {@literal $rank} places the document with the subsequent value at a rank with a gap.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class Rank implements AggregationExpression {
+
+		@Override
+		public Document toDocument(AggregationOperationContext context) {
+			return new Document("$rank", new Document());
+		}
+	}
+
+	/**
+	 * {@link DenseRank} resolves the current document position (the rank) relative to other documents. If multiple
+	 * documents occupy the same rank, {@literal $denseRank} places the document with the subsequent value at the next
+	 * rank without any gaps.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class DenseRank implements AggregationExpression {
+
+		@Override
+		public Document toDocument(AggregationOperationContext context) {
+			return new Document("$denseRank", new Document());
+		}
+	}
+
+	/**
+	 * {@link DocumentNumber} resolves the current document position.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class DocumentNumber implements AggregationExpression {
+
+		@Override
+		public Document toDocument(AggregationOperationContext context) {
+			return new Document("$documentNumber", new Document());
+		}
+	}
+
+	/**
+	 * Shift applies an expression to a document in a specified position relative to the current document.
+	 *
+	 * @author Christoph Strobl
+	 * @since 3.3
+	 */
+	public static class Shift extends AbstractAggregationExpression {
+
+		private Shift(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Specifies the field to evaluate and return.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link Shift}.
+		 */
+		public static Shift shift(String fieldReference) {
+			return new Shift(Collections.singletonMap("output", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Specifies the {@link AggregationExpression expression} to evaluate and return.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link Shift}.
+		 */
+		public static Shift shift(AggregationExpression expression) {
+			return new Shift(Collections.singletonMap("output", expression));
+		}
+
+		/**
+		 * Shift the document position relative to the current. Use a positive value for follow up documents (eg. 1 for the
+		 * next) or a negative value for the predecessor documents (eg. -1 for the previous).
+		 *
+		 * @param shiftBy value to add to the current position.
+		 * @return new instance of {@link Shift}.
+		 */
+		public Shift by(int shiftBy) {
+			return new Shift(append("by", shiftBy));
+		}
+
+		/**
+		 * Define the default value if the target document is out of range.
+		 *
+		 * @param value must not be {@literal null}.
+		 * @return new instance of {@link Shift}.
+		 */
+		public Shift defaultTo(Object value) {
+			return new Shift(append("default", value));
+		}
+
+		/**
+		 * Define the {@link AggregationExpression expression} to evaluate if the target document is out of range.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link Shift}.
+		 */
+		public Shift defaultToValueOf(AggregationExpression expression) {
+			return defaultTo(expression);
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$shift";
+		}
+	}
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/EvaluationOperators.java

@@ -0,0 +1,155 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.core.aggregation;
+
+import org.bson.Document;
+
+import org.springframework.data.mongodb.core.query.CriteriaDefinition;
+import org.springframework.util.Assert;
+
+/**
+ * Gateway to {@literal evaluation operators} such as {@literal $expr}.
+ *
+ * @author Divya Srivastava
+ * @since 3.3
+ */
+public class EvaluationOperators {
+
+	/**
+	 * Take the value resulting from the given fieldReference.
+	 *
+	 * @param fieldReference must not be {@literal null}.
+	 * @return new instance of {@link EvaluationOperatorFactory}.
+	 */
+	public static EvaluationOperatorFactory valueOf(String fieldReference) {
+		return new EvaluationOperatorFactory(fieldReference);
+	}
+
+	/**
+	 * Take the value resulting from the given {@link AggregationExpression}.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @return new instance of {@link EvaluationOperatorFactory}.
+	 */
+	public static EvaluationOperatorFactory valueOf(AggregationExpression expression) {
+		return new EvaluationOperatorFactory(expression);
+	}
+
+	public static class EvaluationOperatorFactory {
+
+		private final String fieldReference;
+		private final AggregationExpression expression;
+
+		/**
+		 * Creates new {@link EvaluationOperatorFactory} for given {@literal fieldReference}.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 */
+		public EvaluationOperatorFactory(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+			this.fieldReference = fieldReference;
+			this.expression = null;
+		}
+
+		/**
+		 * Creates new {@link EvaluationOperatorFactory} for given {@link AggregationExpression}.
+		 *
+		 * @param expression must not be {@literal null}.
+		 */
+		public EvaluationOperatorFactory(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+			this.fieldReference = null;
+			this.expression = expression;
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that is a valid aggregation expression.
+		 *
+		 * @return new instance of {@link Expr}.
+		 */
+		public Expr expr() {
+			return usesFieldRef() ? Expr.valueOf(fieldReference) : Expr.valueOf(expression);
+		}
+
+		/**
+		 * Allows the use of aggregation expressions within the query language.
+		 */
+		public static class Expr extends AbstractAggregationExpression {
+
+			private Expr(Object value) {
+				super(value);
+			}
+
+			@Override
+			protected String getMongoMethod() {
+				return "$expr";
+			}
+
+			/**
+			 * Creates new {@link Expr}.
+			 *
+			 * @param fieldReference must not be {@literal null}.
+			 * @return new instance of {@link Expr}.
+			 */
+			public static Expr valueOf(String fieldReference) {
+
+				Assert.notNull(fieldReference, "FieldReference must not be null!");
+				return new Expr(Fields.field(fieldReference));
+			}
+
+			/**
+			 * Creates new {@link Expr}.
+			 *
+			 * @param expression must not be {@literal null}.
+			 * @return new instance of {@link Expr}.
+			 */
+			public static Expr valueOf(AggregationExpression expression) {
+
+				Assert.notNull(expression, "Expression must not be null!");
+				return new Expr(expression);
+			}
+
+			/**
+			 * Creates {@code $expr} as {@link CriteriaDefinition}.
+			 *
+			 * @return the {@link CriteriaDefinition} from this expression.
+			 */
+			public CriteriaDefinition toCriteriaDefinition(AggregationOperationContext context) {
+
+				Document criteriaObject = toDocument(context);
+
+				return new CriteriaDefinition() {
+					@Override
+					public Document getCriteriaObject() {
+						return criteriaObject;
+					}
+
+					@Override
+					public String getKey() {
+						return getMongoMethod();
+					}
+				};
+			}
+		}
+
+		private boolean usesFieldRef() {
+			return fieldReference != null;
+		}
+	}
+
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/GraphLookupOperation.java

@@ -36,8 +36,7 @@ import org.springframework.util.ClassUtils;
  * We recommend to use the static factory method {@link Aggregation#graphLookup(String)} instead of creating instances
  * of this class directly.
  *
- * @see <a href=
- *      "https://docs.mongodb.org/manual/reference/aggregation/graphLookup/">https://docs.mongodb.org/manual/reference/aggregation/graphLookup/</a>
+ * @see <a href="https://docs.mongodb.org/manual/reference/aggregation/graphLookup/">https://docs.mongodb.org/manual/reference/aggregation/graphLookup/</a>
  * @author Mark Paluch
  * @author Christoph Strobl
  * @since 1.10

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/GroupOperation.java

@@ -139,7 +139,7 @@ public class GroupOperation implements FieldsExposingAggregationOperation {
 	 * Generates an {@link GroupOperationBuilder} for a {@code $sum}-expression.
 	 * <p>
 	 * Count expressions are emulated via {@code $sum: 1}.
-	 * <p>
+	 * </p>
 	 *
 	 * @return
 	 */

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/MatchOperation.java

@@ -16,6 +16,7 @@
 package org.springframework.data.mongodb.core.aggregation;
 
 import org.bson.Document;
+
 import org.springframework.data.mongodb.core.query.CriteriaDefinition;
 import org.springframework.util.Assert;
 
@@ -29,6 +30,7 @@ import org.springframework.util.Assert;
  * @author Sebastian Herold
  * @author Thomas Darimont
  * @author Oliver Gierke
+ * @author Divya Srivastava
  * @since 1.3
  * @see <a href="https://docs.mongodb.com/manual/reference/operator/aggregation/match/">MongoDB Aggregation Framework:
  *      $match</a>
@@ -36,6 +38,7 @@ import org.springframework.util.Assert;
 public class MatchOperation implements AggregationOperation {
 
 	private final CriteriaDefinition criteriaDefinition;
+	private final AggregationExpression expression;
 
 	/**
 	 * Creates a new {@link MatchOperation} for the given {@link CriteriaDefinition}.
@@ -45,7 +48,23 @@ public class MatchOperation implements AggregationOperation {
 	public MatchOperation(CriteriaDefinition criteriaDefinition) {
 
 		Assert.notNull(criteriaDefinition, "Criteria must not be null!");
+
 		this.criteriaDefinition = criteriaDefinition;
+		this.expression = null;
+	}
+
+	/**
+	 * Creates a new {@link MatchOperation} for the given {@link AggregationExpression}.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @since 3.3
+	 */
+	public MatchOperation(AggregationExpression expression) {
+
+		Assert.notNull(expression, "Expression must not be null!");
+
+		this.criteriaDefinition = null;
+		this.expression = expression;
 	}
 
 	/*
@@ -54,7 +73,9 @@ public class MatchOperation implements AggregationOperation {
 	 */
 	@Override
 	public Document toDocument(AggregationOperationContext context) {
-		return new Document(getOperator(), context.getMappedObject(criteriaDefinition.getCriteriaObject()));
+
+		return new Document(getOperator(),
+				context.getMappedObject(expression != null ? expression.toDocument() : criteriaDefinition.getCriteriaObject()));
 	}
 
 	/*

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/PrefixingDelegatingAggregationOperationContext.java

@@ -30,7 +30,7 @@ import org.springframework.lang.Nullable;
 /**
  * {@link AggregationOperationContext} implementation prefixing non-command keys on root level with the given prefix.
  * Useful when mapping fields to domain specific types while having to prefix keys for query purpose.
- * <p />
+ * <br />
  * Fields to be excluded from prefixing my be added to a {@literal denylist}.
  *
  * @author Christoph Strobl

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/RedactOperation.java

@@ -33,8 +33,7 @@ import org.springframework.util.Assert;
  * </pre>
  *
  * @author Christoph Strobl
- * @see <a href=
- *      "https://docs.mongodb.com/manual/reference/operator/aggregation/redact/">https://docs.mongodb.com/manual/reference/operator/aggregation/redact/</a>
+ * @see <a href="https://docs.mongodb.com/manual/reference/operator/aggregation/redact/">https://docs.mongodb.com/manual/reference/operator/aggregation/redact/</a>
  * @since 3.0
  */
 public class RedactOperation implements AggregationOperation {

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/RelaxedTypeBasedAggregationOperationContext.java

@@ -15,6 +15,7 @@
  */
 package org.springframework.data.mongodb.core.aggregation;
 
+import org.springframework.data.mapping.MappingException;
 import org.springframework.data.mapping.context.InvalidPersistentPropertyPath;
 import org.springframework.data.mapping.context.MappingContext;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.DirectFieldReference;
@@ -55,7 +56,7 @@ public class RelaxedTypeBasedAggregationOperationContext extends TypeBasedAggreg
 
 		try {
 			return super.getReferenceFor(field);
-		} catch (InvalidPersistentPropertyPath e) {
+		} catch (MappingException e) {
 			return new DirectFieldReference(new ExposedField(field, true));
 		}
 	}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ReplaceRootOperation.java

@@ -21,6 +21,7 @@ import java.util.Collections;
 import java.util.List;
 
 import org.bson.Document;
+
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.ExposedField;
 import org.springframework.expression.spel.ast.Projection;
 import org.springframework.util.Assert;

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/ScriptOperators.java

@@ -30,7 +30,7 @@ import org.springframework.util.CollectionUtils;
 
 /**
  * Gateway to {@literal $function} and {@literal $accumulator} aggregation operations.
- * <p />
+ * <br />
  * Using {@link ScriptOperators} as part of the {@link Aggregation} requires MongoDB server to have
  * <a href="https://docs.mongodb.com/master/core/server-side-javascript/">server-side JavaScript</a> execution
  * <a href="https://docs.mongodb.com/master/reference/configuration-options/#security.javascriptEnabled">enabled</a>.
@@ -43,7 +43,7 @@ public class ScriptOperators {
 
 	/**
 	 * Create a custom aggregation
-	 * <a href="https://docs.mongodb.com/master/reference/operator/aggregation/function/">$function<a /> in JavaScript.
+	 * <a href="https://docs.mongodb.com/master/reference/operator/aggregation/function/">$function</a> in JavaScript.
 	 *
 	 * @param body The function definition. Must not be {@literal null}.
 	 * @return new instance of {@link Function}.
@@ -53,8 +53,8 @@ public class ScriptOperators {
 	}
 
 	/**
-	 * Create a custom <a href="https://docs.mongodb.com/master/reference/operator/aggregation/accumulator/">$accumulator
-	 * operator</a> in Javascript.
+	 * Create a custom <a href="https://docs.mongodb.com/master/reference/operator/aggregation/accumulator/">$accumulator operator</a>
+	 * in Javascript.
 	 *
 	 * @return new instance of {@link AccumulatorInitBuilder}.
 	 */
@@ -65,7 +65,7 @@ public class ScriptOperators {
 	/**
 	 * {@link Function} defines a custom aggregation
 	 * <a href="https://docs.mongodb.com/master/reference/operator/aggregation/function/">$function</a> in JavaScript.
-	 * <p />
+	 * <br />
 	 * <code class="java">
 	 * {
 	 *   $function: {
@@ -75,7 +75,7 @@ public class ScriptOperators {
 	 *   }
 	 * }
 	 * </code>
-	 * <p />
+	 * <br />
 	 * {@link Function} cannot be used as part of {@link org.springframework.data.mongodb.core.schema.MongoJsonSchema
 	 * schema} validation query expression. <br />
 	 * <b>NOTE:</b> <a href="https://docs.mongodb.com/master/core/server-side-javascript/">Server-Side JavaScript</a>
@@ -179,7 +179,7 @@ public class ScriptOperators {
 	 * <a href="https://docs.mongodb.com/master/reference/operator/aggregation/accumulator/">$accumulator operator</a>,
 	 * one that maintains its state (e.g. totals, maximums, minimums, and related data) as documents progress through the
 	 * pipeline, in JavaScript.
-	 * <p />
+	 * <br />
 	 * <code class="java">
 	 * {
 	 *   $accumulator: {
@@ -193,7 +193,7 @@ public class ScriptOperators {
 	 *   }
 	 * }
 	 * </code>
-	 * <p />
+	 * <br />
 	 * {@link Accumulator} can be used as part of {@link GroupOperation $group}, {@link BucketOperation $bucket} and
 	 * {@link BucketAutoOperation $bucketAuto} pipeline stages. <br />
 	 * <b>NOTE:</b> <a href="https://docs.mongodb.com/master/core/server-side-javascript/">Server-Side JavaScript</a>
@@ -241,7 +241,7 @@ public class ScriptOperators {
 			/**
 			 * Define the {@code init} {@link Function} for the {@link Accumulator accumulators} initial state. The function
 			 * receives its arguments from the {@link Function#args(Object...) initArgs} array expression.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(initArg1, initArg2, ...) {
 			 *   ...
@@ -259,7 +259,7 @@ public class ScriptOperators {
 			/**
 			 * Define the {@code init} function for the {@link Accumulator accumulators} initial state. The function receives
 			 * its arguments from the {@link AccumulatorInitArgsBuilder#initArgs(Object...)} array expression.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(initArg1, initArg2, ...) {
 			 *   ...
@@ -308,7 +308,7 @@ public class ScriptOperators {
 			 * Set the {@code accumulate} {@link Function} that updates the state for each document. The functions first
 			 * argument is the current {@code state}, additional arguments can be defined via {@link Function#args(Object...)
 			 * accumulateArgs}.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(state, accumArg1, accumArg2, ...) {
 			 *   ...
@@ -327,7 +327,7 @@ public class ScriptOperators {
 			 * Set the {@code accumulate} function that updates the state for each document. The functions first argument is
 			 * the current {@code state}, additional arguments can be defined via
 			 * {@link AccumulatorAccumulateArgsBuilder#accumulateArgs(Object...)}.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(state, accumArg1, accumArg2, ...) {
 			 *   ...
@@ -370,7 +370,7 @@ public class ScriptOperators {
 			 * Set the {@code merge} function used to merge two internal states. <br />
 			 * This might be required because the operation is run on a sharded cluster or when the operator exceeds its
 			 * memory limit.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(state1, state2) {
 			 *   ...
@@ -389,7 +389,7 @@ public class ScriptOperators {
 			/**
 			 * Set the {@code finalize} function used to update the result of the accumulation when all documents have been
 			 * processed.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(state) {
 			 *   ...
@@ -425,7 +425,7 @@ public class ScriptOperators {
 			/**
 			 * Define the {@code init} function for the {@link Accumulator accumulators} initial state. The function receives
 			 * its arguments from the {@link #initArgs(Object...)} array expression.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(initArg1, initArg2, ...) {
 			 *   ...
@@ -461,7 +461,7 @@ public class ScriptOperators {
 			/**
 			 * Set the {@code accumulate} function that updates the state for each document. The functions first argument is
 			 * the current {@code state}, additional arguments can be defined via {@link #accumulateArgs(Object...)}.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(state, accumArg1, accumArg2, ...) {
 			 *   ...
@@ -500,7 +500,7 @@ public class ScriptOperators {
 			 * Set the {@code merge} function used to merge two internal states. <br />
 			 * This might be required because the operation is run on a sharded cluster or when the operator exceeds its
 			 * memory limit.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(state1, state2) {
 			 *   ...
@@ -537,7 +537,7 @@ public class ScriptOperators {
 			/**
 			 * Set the {@code finalize} function used to update the result of the accumulation when all documents have been
 			 * processed.
-			 * <p />
+			 * <br />
 			 * <code class="java">
 			 * function(state) {
 			 *   ...

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/SetOperation.java

@@ -193,5 +193,6 @@ public class SetOperation extends DocumentEnhancingOperation {
 			 */
 			SetOperation withValueOfExpression(String operation, Object... values);
 		}
+
 	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/SetWindowFieldsOperation.java

@@ -0,0 +1,873 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.core.aggregation;
+
+import java.time.temporal.ChronoUnit;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.concurrent.TimeUnit;
+
+import org.bson.Document;
+import org.springframework.data.domain.Sort;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * Encapsulates the {@code setWindowFields}-operation.
+ *
+ * @author Christoph Strobl
+ * @since 3.3
+ * @see <a href="https://docs.mongodb.com/manual/reference/operator/aggregation/setWindowFields/">https://docs.mongodb.com/manual/reference/operator/aggregation/setWindowFields/</a>
+ */
+public class SetWindowFieldsOperation
+		implements AggregationOperation, FieldsExposingAggregationOperation.InheritsFieldsAggregationOperation {
+
+	private static final String CURRENT = "current";
+	private static final String UNBOUNDED = "unbounded";
+
+	private final @Nullable Object partitionBy;
+	private final @Nullable AggregationOperation sortBy;
+	private final WindowOutput output;
+
+	/**
+	 * Create a new {@link SetWindowFieldsOperation} with given args.
+	 *
+	 * @param partitionBy The field or {@link AggregationExpression} to group by.
+	 * @param sortBy the {@link SortOperation operation} to sort the documents by in the partition.
+	 * @param output the {@link WindowOutput} containing the fields to add and the rules to calculate their respective
+	 *          values.
+	 */
+	protected SetWindowFieldsOperation(@Nullable Object partitionBy, @Nullable AggregationOperation sortBy,
+			WindowOutput output) {
+
+		this.partitionBy = partitionBy;
+		this.sortBy = sortBy;
+		this.output = output;
+	}
+
+	/**
+	 * Obtain a {@link SetWindowFieldsOperationBuilder builder} to create a {@link SetWindowFieldsOperation}.
+	 *
+	 * @return new instance of {@link SetWindowFieldsOperationBuilder}.
+	 */
+	public static SetWindowFieldsOperationBuilder builder() {
+		return new SetWindowFieldsOperationBuilder();
+	}
+
+	@Override
+	public ExposedFields getFields() {
+		return ExposedFields.nonSynthetic(Fields.from(output.fields.toArray(new Field[0])));
+	}
+
+	@Override
+	public Document toDocument(AggregationOperationContext context) {
+
+		Document $setWindowFields = new Document();
+		if (partitionBy != null) {
+			if (partitionBy instanceof AggregationExpression) {
+				$setWindowFields.append("partitionBy", ((AggregationExpression) partitionBy).toDocument(context));
+			} else if (partitionBy instanceof Field) {
+				$setWindowFields.append("partitionBy", context.getReference((Field) partitionBy).toString());
+			} else {
+				$setWindowFields.append("partitionBy", partitionBy);
+			}
+		}
+
+		if (sortBy != null) {
+			$setWindowFields.append("sortBy", sortBy.toDocument(context).get(sortBy.getOperator()));
+		}
+
+		Document output = new Document();
+		for (ComputedField field : this.output.fields) {
+
+			Document fieldOperation = field.getWindowOperator().toDocument(context);
+			if (field.window != null) {
+				fieldOperation.put("window", field.window.toDocument(context));
+			}
+			output.append(field.getName(), fieldOperation);
+		}
+		$setWindowFields.append("output", output);
+
+		return new Document(getOperator(), $setWindowFields);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#getOperator()
+	 */
+	@Override
+	public String getOperator() {
+		return "$setWindowFields";
+	}
+
+	/**
+	 * {@link WindowOutput} defines output of {@literal $setWindowFields} stage by defining the {@link ComputedField
+	 * field(s)} to append to the documents in the output.
+	 */
+	public static class WindowOutput {
+
+		private final List<ComputedField> fields;
+
+		/**
+		 * Create a new output containing the single given {@link ComputedField field}.
+		 *
+		 * @param outputField must not be {@literal null}.
+		 */
+		public WindowOutput(ComputedField outputField) {
+
+			Assert.notNull(outputField, "OutputField must not be null!");
+
+			this.fields = new ArrayList<>();
+			this.fields.add(outputField);
+		}
+
+		/**
+		 * Append the given {@link ComputedField field} to the outptut.
+		 *
+		 * @param field must not be {@literal null}.
+		 * @return this.
+		 */
+		public WindowOutput append(ComputedField field) {
+
+			Assert.notNull(field, "Field must not be null!");
+
+			fields.add(field);
+			return this;
+		}
+
+		/**
+		 * Append the given {@link AggregationExpression} as a {@link ComputedField field} in a fluent way.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link ComputedFieldAppender}.
+		 * @see #append(ComputedField)
+		 */
+		public ComputedFieldAppender append(AggregationExpression expression) {
+
+			return new ComputedFieldAppender() {
+
+				@Nullable private Window window;
+
+				@Override
+				public WindowOutput as(String fieldname) {
+
+					return WindowOutput.this.append(new ComputedField(fieldname, expression, window));
+				}
+
+				@Override
+				public ComputedFieldAppender within(Window window) {
+					this.window = window;
+					return this;
+				}
+			};
+		}
+
+		/**
+		 * Tiny little helper to allow fluent API usage for {@link #append(ComputedField)}.
+		 */
+		interface ComputedFieldAppender {
+
+			/**
+			 * Specify the target field name.
+			 *
+			 * @param fieldname the name of field to add to the target document.
+			 * @return the {@link WindowOutput} that started the append operation.
+			 */
+			WindowOutput as(String fieldname);
+
+			/**
+			 * Specify the window boundaries.
+			 *
+			 * @param window must not be {@literal null}.
+			 * @return this.
+			 */
+			ComputedFieldAppender within(Window window);
+		}
+	}
+
+	/**
+	 * A {@link Field} that the result of a computation done via an {@link AggregationExpression}.
+	 *
+	 * @author Christoph Strobl
+	 */
+	public static class ComputedField implements Field {
+
+		private final String name;
+		private final AggregationExpression windowOperator;
+		private final @Nullable Window window;
+
+		/**
+		 * Create a new {@link ComputedField}.
+		 *
+		 * @param name the target field name.
+		 * @param windowOperator the expression to calculate the field value.
+		 */
+		public ComputedField(String name, AggregationExpression windowOperator) {
+			this(name, windowOperator, null);
+		}
+
+		/**
+		 * Create a new {@link ComputedField}.
+		 *
+		 * @param name the target field name.
+		 * @param windowOperator the expression to calculate the field value.
+		 * @param window the boundaries to operate within. Can be {@literal null}.
+		 */
+		public ComputedField(String name, AggregationExpression windowOperator, @Nullable Window window) {
+
+			this.name = name;
+			this.windowOperator = windowOperator;
+			this.window = window;
+		}
+
+		@Override
+		public String getName() {
+			return name;
+		}
+
+		@Override
+		public String getTarget() {
+			return getName();
+		}
+
+		@Override
+		public boolean isAliased() {
+			return false;
+		}
+
+		public AggregationExpression getWindowOperator() {
+			return windowOperator;
+		}
+
+		public Window getWindow() {
+			return window;
+		}
+	}
+
+	/**
+	 * Quick access to {@link DocumentWindow documents} and {@literal RangeWindow range} {@link Window windows}.
+	 *
+	 * @author Christoph Strobl
+	 */
+	public interface Windows {
+
+		/**
+		 * Create a document window relative to the position of the current document.
+		 *
+		 * @param lower an integer for a position relative to the current document, {@literal current} or
+		 *          {@literal unbounded}.
+		 * @param upper an integer for a position relative to the current document, {@literal current} or
+		 *          {@literal unbounded}.
+		 * @return new instance of {@link DocumentWindow}.
+		 */
+		static DocumentWindow documents(Object lower, Object upper) {
+			return new DocumentWindow(lower, upper);
+		}
+
+		/**
+		 * Create a range window defined based on sort expression.
+		 *
+		 * @param lower a numeric value to add the sort by field value of the current document, {@literal current} or
+		 *          {@literal unbounded}.
+		 * @param upper a numeric value to add the sort by field value of the current document, {@literal current} or
+		 *          {@literal unbounded}.
+		 * @return new instance of {@link RangeWindow}.
+		 */
+		static RangeWindow range(Object lower, Object upper, @Nullable WindowUnit unit) {
+			return new RangeWindow(lower, upper, unit == null ? WindowUnits.DEFAULT : unit);
+		}
+
+		/**
+		 * Create a range window based on the {@link Sort sort value} of the current document via a fluent API.
+		 *
+		 * @return new instance of {@link RangeWindowBuilder}.
+		 */
+		static RangeWindowBuilder range() {
+			return new RangeWindowBuilder();
+		}
+
+		/**
+		 * Create a document window relative to the position of the current document via a fluent API.
+		 *
+		 * @return new instance of {@link DocumentWindowBuilder}.
+		 */
+		static DocumentWindowBuilder documents() {
+			return new DocumentWindowBuilder();
+		}
+	}
+
+	/**
+	 * A {@link Window} to be used for {@link ComputedField#getWindow() ComputedField}.
+	 */
+	public interface Window {
+
+		/**
+		 * The lower (inclusive) boundary.
+		 *
+		 * @return
+		 */
+		Object getLower();
+
+		/**
+		 * The upper (inclusive) boundary.
+		 *
+		 * @return
+		 */
+		Object getUpper();
+
+		/**
+		 * Obtain the document representation of the window in a default {@link AggregationOperationContext context}.
+		 *
+		 * @return never {@literal null}.
+		 */
+		default Document toDocument() {
+			return toDocument(Aggregation.DEFAULT_CONTEXT);
+		}
+
+		/**
+		 * Obtain the document representation of the window in the given {@link AggregationOperationContext context}.
+		 *
+		 * @return never {@literal null}.
+		 */
+		Document toDocument(AggregationOperationContext ctx);
+	}
+
+	/**
+	 * Builder API for a {@link RangeWindow}.
+	 *
+	 * @author Christoph Strobl
+	 */
+	public static class RangeWindowBuilder {
+
+		private @Nullable Object lower;
+		private @Nullable Object upper;
+		private @Nullable WindowUnit unit;
+
+		/**
+		 * The lower (inclusive) range limit based on the sortBy field.
+		 *
+		 * @param lower eg. {@literal current} or {@literal unbounded}.
+		 * @return this.
+		 */
+		public RangeWindowBuilder from(String lower) {
+
+			this.lower = lower;
+			return this;
+		}
+
+		/**
+		 * The upper (inclusive) range limit based on the sortBy field.
+		 *
+		 * @param upper eg. {@literal current} or {@literal unbounded}.
+		 * @return this.
+		 */
+		public RangeWindowBuilder to(String upper) {
+
+			this.upper = upper;
+			return this;
+		}
+
+		/**
+		 * The lower (inclusive) range limit value to add to the value based on the sortBy field. Use a negative integer for
+		 * a position before the current document. Use a positive integer for a position after the current document.
+		 * {@code 0} is the current document position.
+		 *
+		 * @param lower
+		 * @return this.
+		 */
+		public RangeWindowBuilder from(Number lower) {
+
+			this.lower = lower;
+			return this;
+		}
+
+		/**
+		 * The upper (inclusive) range limit value to add to the value based on the sortBy field. Use a negative integer for
+		 * a position before the current document. Use a positive integer for a position after the current document.
+		 * {@code 0} is the current document position.
+		 *
+		 * @param upper
+		 * @return this.
+		 */
+		public RangeWindowBuilder to(Number upper) {
+
+			this.upper = upper;
+			return this;
+		}
+
+		/**
+		 * Use {@literal current} as {@link #from(String) lower} limit.
+		 *
+		 * @return this.
+		 */
+		public RangeWindowBuilder fromCurrent() {
+			return from(CURRENT);
+		}
+
+		/**
+		 * Use {@literal unbounded} as {@link #from(String) lower} limit.
+		 *
+		 * @return this.
+		 */
+		public RangeWindowBuilder fromUnbounded() {
+			return from(UNBOUNDED);
+		}
+
+		/**
+		 * Use {@literal current} as {@link #to(String) upper} limit.
+		 *
+		 * @return this.
+		 */
+		public RangeWindowBuilder toCurrent() {
+			return to(CURRENT);
+		}
+
+		/**
+		 * Use {@literal unbounded} as {@link #to(String) upper} limit.
+		 *
+		 * @return this.
+		 */
+		public RangeWindowBuilder toUnbounded() {
+			return to(UNBOUNDED);
+		}
+
+		/**
+		 * Set the {@link WindowUnit unit} or measure for the given {@link Window}.
+		 *
+		 * @param windowUnit must not be {@literal null}. Can be on of {@link Windows}.
+		 * @return this.
+		 */
+		public RangeWindowBuilder unit(WindowUnit windowUnit) {
+
+			Assert.notNull(windowUnit, "WindowUnit must not be null");
+			this.unit = windowUnit;
+			return this;
+		}
+
+		/**
+		 * Build the {@link RangeWindow}.
+		 *
+		 * @return new instance of {@link RangeWindow}.
+		 */
+		public RangeWindow build() {
+
+			Assert.notNull(lower, "Lower bound must not be null");
+			Assert.notNull(upper, "Upper bound must not be null");
+			Assert.notNull(unit, "WindowUnit bound must not be null");
+
+			return new RangeWindow(lower, upper, unit);
+		}
+	}
+
+	/**
+	 * Builder API for a {@link RangeWindow}.
+	 *
+	 * @author Christoph Strobl
+	 */
+	public static class DocumentWindowBuilder {
+
+		private @Nullable Object lower;
+		private @Nullable Object upper;
+
+		/**
+		 * The lower (inclusive) range limit based on current document. Use a negative integer for a position before the
+		 * current document. Use a positive integer for a position after the current document. {@code 0} is the current
+		 * document position.
+		 *
+		 * @param lower
+		 * @return this.
+		 */
+		public DocumentWindowBuilder from(Number lower) {
+
+			this.lower = lower;
+			return this;
+		}
+
+		public DocumentWindowBuilder fromCurrent() {
+			return from(CURRENT);
+		}
+
+		public DocumentWindowBuilder fromUnbounded() {
+			return from(UNBOUNDED);
+		}
+
+		public DocumentWindowBuilder to(String upper) {
+
+			this.upper = upper;
+			return this;
+		}
+
+		/**
+		 * The lower (inclusive) range limit based on current document.
+		 *
+		 * @param lower eg. {@literal current} or {@literal unbounded}.
+		 * @return this.
+		 */
+		public DocumentWindowBuilder from(String lower) {
+
+			this.lower = lower;
+			return this;
+		}
+
+		/**
+		 * The upper (inclusive) range limit based on current document. Use a negative integer for a position before the
+		 * current document. Use a positive integer for a position after the current document. {@code 0} is the current
+		 * document position.
+		 *
+		 * @param upper
+		 * @return this.
+		 */
+		public DocumentWindowBuilder to(Number upper) {
+
+			this.upper = upper;
+			return this;
+		}
+
+		public DocumentWindowBuilder toCurrent() {
+			return to(CURRENT);
+		}
+
+		public DocumentWindowBuilder toUnbounded() {
+			return to(UNBOUNDED);
+		}
+
+		public DocumentWindow build() {
+
+			Assert.notNull(lower, "Lower bound must not be null");
+			Assert.notNull(upper, "Upper bound must not be null");
+
+			return new DocumentWindow(lower, upper);
+		}
+	}
+
+	/**
+	 * Common base class for {@link Window} implementation.
+	 *
+	 * @author Christoph Strobl
+	 */
+	static abstract class WindowImpl implements Window {
+
+		private final Object lower;
+		private final Object upper;
+
+		protected WindowImpl(Object lower, Object upper) {
+			this.lower = lower;
+			this.upper = upper;
+		}
+
+		@Override
+		public Object getLower() {
+			return lower;
+		}
+
+		@Override
+		public Object getUpper() {
+			return upper;
+		}
+	}
+
+	/**
+	 * {@link Window} implementation based on the current document.
+	 *
+	 * @author Christoph Strobl
+	 */
+	public static class DocumentWindow extends WindowImpl {
+
+		DocumentWindow(Object lower, Object upper) {
+			super(lower, upper);
+		}
+
+		@Override
+		public Document toDocument(AggregationOperationContext ctx) {
+			return new Document("documents", Arrays.asList(getLower(), getUpper()));
+		}
+	}
+
+	/**
+	 * {@link Window} implementation based on the sort fields.
+	 *
+	 * @author Christoph Strobl
+	 */
+	public static class RangeWindow extends WindowImpl {
+
+		private final WindowUnit unit;
+
+		protected RangeWindow(Object lower, Object upper, WindowUnit unit) {
+
+			super(lower, upper);
+			this.unit = unit;
+		}
+
+		@Override
+		public Document toDocument(AggregationOperationContext ctx) {
+
+			Document range = new Document("range", new Object[] { getLower(), getUpper() });
+			if (unit != null && !WindowUnits.DEFAULT.equals(unit)) {
+				range.append("unit", unit.name().toLowerCase());
+			}
+			return range;
+		}
+	}
+
+	/**
+	 * The actual time unit to apply to a {@link Window}.
+	 */
+	public interface WindowUnit {
+
+		String name();
+
+		/**
+		 * Converts the given time unit into a {@link WindowUnit}. Supported units are: days, hours, minutes, seconds, and
+		 * milliseconds.
+		 *
+		 * @param timeUnit the time unit to convert, must not be {@literal null}.
+		 * @return
+		 * @throws IllegalArgumentException if the {@link TimeUnit} is {@literal null} or not supported for conversion.
+		 */
+		static WindowUnit from(TimeUnit timeUnit) {
+
+			Assert.notNull(timeUnit, "TimeUnit must not be null");
+
+			switch (timeUnit) {
+				case DAYS:
+					return WindowUnits.DAY;
+				case HOURS:
+					return WindowUnits.HOUR;
+				case MINUTES:
+					return WindowUnits.MINUTE;
+				case SECONDS:
+					return WindowUnits.SECOND;
+				case MILLISECONDS:
+					return WindowUnits.MILLISECOND;
+			}
+
+			throw new IllegalArgumentException(String.format("Cannot create WindowUnit from %s", timeUnit));
+		}
+
+		/**
+		 * Converts the given chrono unit into a {@link WindowUnit}. Supported units are: years, weeks, months, days, hours,
+		 * minutes, seconds, and millis.
+		 *
+		 * @param chronoUnit the chrono unit to convert, must not be {@literal null}.
+		 * @return
+		 * @throws IllegalArgumentException if the {@link TimeUnit} is {@literal null} or not supported for conversion.
+		 */
+		static WindowUnit from(ChronoUnit chronoUnit) {
+
+			switch (chronoUnit) {
+				case YEARS:
+					return WindowUnits.YEAR;
+				case WEEKS:
+					return WindowUnits.WEEK;
+				case MONTHS:
+					return WindowUnits.MONTH;
+				case DAYS:
+					return WindowUnits.DAY;
+				case HOURS:
+					return WindowUnits.HOUR;
+				case MINUTES:
+					return WindowUnits.MINUTE;
+				case SECONDS:
+					return WindowUnits.SECOND;
+				case MILLIS:
+					return WindowUnits.MILLISECOND;
+			}
+
+			throw new IllegalArgumentException(String.format("Cannot create WindowUnit from %s", chronoUnit));
+		}
+	}
+
+	/**
+	 * Quick access to available {@link WindowUnit units}.
+	 */
+	public enum WindowUnits implements WindowUnit {
+		DEFAULT, YEAR, QUARTER, MONTH, WEEK, DAY, HOUR, MINUTE, SECOND, MILLISECOND
+	}
+
+	/**
+	 * A fluent builder to create a {@link SetWindowFieldsOperation}.
+	 *
+	 * @author Christoph Strobl
+	 */
+	public static class SetWindowFieldsOperationBuilder {
+
+		private Object partitionBy;
+		private SortOperation sortOperation;
+		private WindowOutput output;
+
+		/**
+		 * Specify the field to group by.
+		 *
+		 * @param fieldName must not be {@literal null} or null.
+		 * @return this.
+		 */
+		public SetWindowFieldsOperationBuilder partitionByField(String fieldName) {
+
+			Assert.hasText(fieldName, "Field name must not be empty or null");
+			return partitionBy(Fields.field("$" + fieldName, fieldName));
+		}
+
+		/**
+		 * Specify the {@link AggregationExpression expression} to group by.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return this.
+		 */
+		public SetWindowFieldsOperationBuilder partitionByExpression(AggregationExpression expression) {
+			return partitionBy(expression);
+		}
+
+		/**
+		 * Sort {@link Sort.Direction#ASC ascending} by the given fields.
+		 *
+		 * @param fields must not be {@literal null}.
+		 * @return this.
+		 */
+		public SetWindowFieldsOperationBuilder sortBy(String... fields) {
+			return sortBy(Sort.by(fields));
+		}
+
+		/**
+		 * Set the sort order.
+		 *
+		 * @param sort must not be {@literal null}.
+		 * @return this.
+		 */
+		public SetWindowFieldsOperationBuilder sortBy(Sort sort) {
+			return sortBy(new SortOperation(sort));
+		}
+
+		/**
+		 * Set the {@link SortOperation} to use.
+		 *
+		 * @param sort must not be {@literal null}.
+		 * @return this.
+		 */
+		public SetWindowFieldsOperationBuilder sortBy(SortOperation sort) {
+
+			Assert.notNull(sort, "SortOperation must not be null");
+
+			this.sortOperation = sort;
+			return this;
+		}
+
+		/**
+		 * Define the actual output computation.
+		 *
+		 * @param output must not be {@literal null}.
+		 * @return this.
+		 */
+		public SetWindowFieldsOperationBuilder output(WindowOutput output) {
+
+			Assert.notNull(output, "WindowOutput must not be null");
+
+			this.output = output;
+			return this;
+		}
+
+		/**
+		 * Add a field capturing the result of the given {@link AggregationExpression expression} to the output.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link WindowChoice}.
+		 */
+		public WindowChoice output(AggregationExpression expression) {
+
+			return new WindowChoice() {
+
+				@Nullable private Window window;
+
+				@Override
+				public As within(Window window) {
+
+					Assert.notNull(window, "Window must not be null");
+
+					this.window = window;
+					return this;
+				}
+
+				@Override
+				public SetWindowFieldsOperationBuilder as(String targetFieldName) {
+
+					Assert.hasText(targetFieldName, "Target field name must not be empty or null");
+
+					ComputedField computedField = new ComputedField(targetFieldName, expression, window);
+
+					if (SetWindowFieldsOperationBuilder.this.output == null) {
+						SetWindowFieldsOperationBuilder.this.output = new WindowOutput(computedField);
+					} else {
+						SetWindowFieldsOperationBuilder.this.output.append(computedField);
+					}
+
+					return SetWindowFieldsOperationBuilder.this;
+				}
+			};
+		}
+
+		/**
+		 * Interface to capture field name used to capture the computation result.
+		 */
+		public interface As {
+
+			/**
+			 * Define the target name field name to hold the computation result.
+			 *
+			 * @param targetFieldName must not be {@literal null} or empty.
+			 * @return the starting point {@link SetWindowFieldsOperationBuilder builder} instance.
+			 */
+			SetWindowFieldsOperationBuilder as(String targetFieldName);
+		}
+
+		/**
+		 * Interface to capture an optional {@link Window} applicable to the field computation.
+		 */
+		public interface WindowChoice extends As {
+
+			/**
+			 * Specify calculation boundaries.
+			 *
+			 * @param window must not be {@literal null}.
+			 * @return never {@literal null}.
+			 */
+			As within(Window window);
+
+		}
+
+		/**
+		 * Partition by a value that translates to a valid mongodb expression.
+		 *
+		 * @param value must not be {@literal null}.
+		 * @return this.
+		 */
+		public SetWindowFieldsOperationBuilder partitionBy(Object value) {
+
+			Assert.notNull(value, "Partition By must not be null");
+
+			partitionBy = value;
+			return this;
+		}
+
+		/**
+		 * Obtain a new instance of {@link SetWindowFieldsOperation} with previously set arguments.
+		 *
+		 * @return new instance of {@link SetWindowFieldsOperation}.
+		 */
+		public SetWindowFieldsOperation build() {
+			return new SetWindowFieldsOperation(partitionBy, sortOperation, output);
+		}
+	}
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/SortByCountOperation.java

@@ -21,17 +21,16 @@ import org.springframework.util.Assert;
 
 /**
  * Encapsulates the aggregation framework {@code $sortByCount}-operation.
- * <p/>
+ * <br />
  * {@code $sortByCount} stage is typically used with {@link Aggregation} and {@code $facet}. Groups incoming documents
  * based on the value of a specified expression and computes the count of documents in each distinct group.
  * {@link SortByCountOperation} is equivalent to {@code { $group: { _id: <expression>, count: { $sum: 1 } } }, { $sort:
  * { count: -1 } }}.
- * <p/>
+ * <br />
  * We recommend to use the static factory method {@link Aggregation#sortByCount(String)} instead of creating instances
  * of this class directly.
  *
- * @see <a href=
- *      "https://docs.mongodb.com/manual/reference/operator/aggregation/sortByCount/">https://docs.mongodb.com/manual/reference/operator/aggregation/sortByCount/</a>
+ * @see <a href="https://docs.mongodb.com/manual/reference/operator/aggregation/sortByCount/">https://docs.mongodb.com/manual/reference/operator/aggregation/sortByCount/</a>
  * @author Jérôme Guyon
  * @author Mark Paluch
  * @since 2.1

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/SpelExpressionTransformer.java

@@ -102,7 +102,7 @@ class SpelExpressionTransformer implements AggregationExpressionTransformer {
 		ExpressionState state = new ExpressionState(new StandardEvaluationContext(params), CONFIG);
 		ExpressionNode node = ExpressionNode.from(spelExpression.getAST(), state);
 
-		return transform(new AggregationExpressionTransformationContext<ExpressionNode>(node, null, null, context));
+		return transform(new AggregationExpressionTransformationContext<>(node, null, null, context));
 	}
 
 	/*
@@ -500,7 +500,10 @@ class SpelExpressionTransformer implements AggregationExpressionTransformer {
 					dbo.put(methodReference.getArgumentMap()[i++], transform(child, context));
 				}
 				args = dbo;
-			} else {
+			} else if (ObjectUtils.nullSafeEquals(methodReference.getArgumentType(), ArgumentType.EMPTY_DOCUMENT)) {
+				args = new Document();
+			}
+			else {
 
 				List<Object> argList = new ArrayList<Object>();
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/StringOperators.java

@@ -18,8 +18,11 @@ package org.springframework.data.mongodb.core.aggregation;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Map;
+import java.util.regex.Pattern;
 
 import org.springframework.data.domain.Range;
+import org.springframework.data.mongodb.util.RegexFlags;
 import org.springframework.util.Assert;
 
 /**
@@ -27,6 +30,7 @@ import org.springframework.util.Assert;
  *
  * @author Christoph Strobl
  * @author Mark Paluch
+ * @author Divya Srivastava
  * @since 1.10
  */
 public class StringOperators {
@@ -516,6 +520,173 @@ public class StringOperators {
 			return usesFieldRef() ? RTrim.valueOf(fieldReference) : RTrim.valueOf(expression);
 		}
 
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and applies the given
+		 * regular expression to find the document with the first match.<br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param regex must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 * @since 3.3
+		 */
+		public RegexFind regexFind(String regex) {
+			return createRegexFind().regex(regex);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and applies the regular
+		 * expression resulting from the given {@link AggregationExpression} to find the document with the first
+		 * match.<br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 * @since 3.3
+		 */
+		public RegexFind regexFind(AggregationExpression expression) {
+			return createRegexFind().regexOf(expression);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the {@link Pattern} and applies the regular expression with
+		 * the options specified in the argument to find the document with the first match.
+		 *
+		 * @param pattern the pattern object to apply.
+		 * @return new instance of {@link RegexFind}.
+		 * @since 3.3
+		 */
+		public RegexFind regexFind(Pattern pattern) {
+			return createRegexFind().pattern(pattern);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and applies the regular
+		 * expression with the options specified in the argument to find the document with the first match.
+		 *
+		 * @param regex the regular expression to apply.
+		 * @param options the options to use.
+		 * @return new instance of {@link RegexFind}.
+		 * @since 3.3
+		 */
+		public RegexFind regexFind(String regex, String options) {
+			return createRegexFind().regex(regex).options(options);
+		}
+
+		private RegexFind createRegexFind() {
+			return usesFieldRef() ? RegexFind.valueOf(fieldReference) : RegexFind.valueOf(expression);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and applies the given
+		 * regular expression to find all the documents with the match.<br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param regex must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 * @since 3.3
+		 */
+		public RegexFindAll regexFindAll(String regex) {
+			return createRegexFindAll().regex(regex);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and applies the regular
+		 * expression resulting from the given {@link AggregationExpression} to find all the documents with the
+		 * match..<br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 * @since 3.3
+		 */
+		public RegexFindAll regexFindAll(AggregationExpression expression) {
+			return createRegexFindAll().regexOf(expression);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes a {@link Pattern} and applies the regular expression with
+		 * the options specified in the argument to find all the documents with the match.
+		 *
+		 * @param pattern the pattern object to apply.
+		 * @return new instance of {@link RegexFindAll}.
+		 * @since 3.3
+		 */
+		public RegexFindAll regexFindAll(Pattern pattern) {
+			return createRegexFindAll().pattern(pattern);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and applies the regular
+		 * expression with the options specified in the argument to find all the documents with the match.
+		 *
+		 * @param regex the regular expression to apply.
+		 * @param options the options to use.
+		 * @return new instance of {@link RegexFindAll}.
+		 * @since 3.3
+		 */
+		public RegexFindAll regexFindAll(String regex, String options) {
+			return createRegexFindAll().regex(regex).options(options);
+		}
+
+		private RegexFindAll createRegexFindAll() {
+			return usesFieldRef() ? RegexFindAll.valueOf(fieldReference) : RegexFindAll.valueOf(expression);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and applies the given
+		 * regular expression to find if a match is found or not.<br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param regex must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 * @since 3.3
+		 */
+		public RegexMatch regexMatch(String regex) {
+			return createRegexMatch().regex(regex);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and applies the regular
+		 * expression resulting from the given {@link AggregationExpression} to find if a match is found or not.<br />
+		 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 * @since 3.3
+		 */
+		public RegexMatch regexMatch(AggregationExpression expression) {
+			return createRegexMatch().regexOf(expression);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes a {@link Pattern} and applies the regular expression with
+		 * the options specified in the argument to find if a match is found or not.
+		 *
+		 * @param pattern the pattern object to apply.
+		 * @return new instance of {@link RegexMatch}.
+		 * @since 3.3
+		 */
+		public RegexMatch regexMatch(Pattern pattern) {
+			return createRegexMatch().pattern(pattern);
+		}
+
+		/**
+		 * Creates new {@link AggregationExpression} that takes the associated string representation and applies the regular
+		 * expression with the options specified in the argument to find if a match is found or not.
+		 *
+		 * @param regex the regular expression to apply.
+		 * @param options the options to use.
+		 * @return new instance of {@link RegexMatch}.
+		 * @since 3.3
+		 */
+		public RegexMatch regexMatch(String regex, String options) {
+			return createRegexMatch().regex(regex).options(options);
+		}
+
+		private RegexMatch createRegexMatch() {
+			return usesFieldRef() ? RegexMatch.valueOf(fieldReference) : RegexMatch.valueOf(expression);
+		}
+
 		private boolean usesFieldRef() {
 			return fieldReference != null;
 		}
@@ -1477,4 +1648,434 @@ public class StringOperators {
 			return "$rtrim";
 		}
 	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $regexFind} which applies a regular expression (regex) to a string and
+	 * returns information on the first matched substring. <br />
+	 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+	 *
+	 * @author Divya Srivastava
+	 * @since 3.3
+	 */
+	public static class RegexFind extends AbstractAggregationExpression {
+
+		protected RegexFind(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates new {@link RegexFind} using the value of the provided {@link Field fieldReference} as {@literal input}
+		 * value.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 */
+		public static RegexFind valueOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+
+			return new RegexFind(Collections.singletonMap("input", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Creates new {@link RegexFind} using the result of the provided {@link AggregationExpression} as {@literal input}
+		 * value.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 */
+		public static RegexFind valueOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+
+			return new RegexFind(Collections.singletonMap("input", expression));
+		}
+
+		/**
+		 * Optional specify the options to use with the regular expression.
+		 *
+		 * @param options must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 */
+		public RegexFind options(String options) {
+
+			Assert.notNull(options, "Options must not be null!");
+
+			return new RegexFind(append("options", options));
+		}
+
+		/**
+		 * Optional specify the reference to the {@link Field field} holding the options values to use with the regular
+		 * expression.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 */
+		public RegexFind optionsOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+
+			return new RegexFind(append("options", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Optional specify the {@link AggregationExpression} evaluating to the options values to use with the regular
+		 * expression.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 */
+		public RegexFind optionsOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+
+			return new RegexFind(append("options", expression));
+		}
+
+		/**
+		 * Specify the regular expression to apply.
+		 *
+		 * @param regex must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 */
+		public RegexFind regex(String regex) {
+
+			Assert.notNull(regex, "Regex must not be null!");
+
+			return new RegexFind(append("regex", regex));
+		}
+
+		/**
+		 * Apply a {@link Pattern} into {@code regex} and {@code options} fields.
+		 *
+		 * @param pattern must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 */
+		public RegexFind pattern(Pattern pattern) {
+
+			Assert.notNull(pattern, "Pattern must not be null!");
+
+			Map<String, Object> regex = append("regex", pattern.pattern());
+			regex.put("options", RegexFlags.toRegexOptions(pattern.flags()));
+
+			return new RegexFind(regex);
+		}
+
+		/**
+		 * Specify the reference to the {@link Field field} holding the regular expression to apply.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 */
+		public RegexFind regexOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "fieldReference must not be null!");
+
+			return new RegexFind(append("regex", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Specify the {@link AggregationExpression} evaluating to the regular expression to apply.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexFind}.
+		 */
+		public RegexFind regexOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+
+			return new RegexFind(append("regex", expression));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$regexFind";
+		}
+	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $regexFindAll} which applies a regular expression (regex) to a string and
+	 * returns information on all the matched substrings. <br />
+	 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+	 *
+	 * @author Divya Srivastava
+	 * @since 3.3
+	 */
+	public static class RegexFindAll extends AbstractAggregationExpression {
+
+		protected RegexFindAll(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates new {@link RegexFindAll} using the value of the provided {@link Field fieldReference} as {@literal input}
+		 * value.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 */
+		public static RegexFindAll valueOf(String fieldReference) {
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+			return new RegexFindAll(Collections.singletonMap("input", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Creates new {@link RegexFindAll} using the result of the provided {@link AggregationExpression} as
+		 * {@literal input} value.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 */
+		public static RegexFindAll valueOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+
+			return new RegexFindAll(Collections.singletonMap("input", expression));
+		}
+
+		/**
+		 * Optional specify the options to use with the regular expression.
+		 *
+		 * @param options must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 */
+		public RegexFindAll options(String options) {
+
+			Assert.notNull(options, "Options must not be null!");
+
+			return new RegexFindAll(append("options", options));
+		}
+
+		/**
+		 * Optional specify the reference to the {@link Field field} holding the options values to use with the regular
+		 * expression.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 */
+		public RegexFindAll optionsOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "fieldReference must not be null!");
+
+			return new RegexFindAll(append("options", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Optional specify the {@link AggregationExpression} evaluating to the options values to use with the regular
+		 * expression.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 */
+		public RegexFindAll optionsOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+
+			return new RegexFindAll(append("options", expression));
+		}
+
+		/**
+		 * Apply a {@link Pattern} into {@code regex} and {@code options} fields.
+		 *
+		 * @param pattern must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 */
+		public RegexFindAll pattern(Pattern pattern) {
+
+			Assert.notNull(pattern, "Pattern must not be null!");
+
+			Map<String, Object> regex = append("regex", pattern.pattern());
+			regex.put("options", RegexFlags.toRegexOptions(pattern.flags()));
+
+			return new RegexFindAll(regex);
+		}
+
+		/**
+		 * Specify the regular expression to apply.
+		 *
+		 * @param regex must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 */
+		public RegexFindAll regex(String regex) {
+
+			Assert.notNull(regex, "Regex must not be null!");
+
+			return new RegexFindAll(append("regex", regex));
+		}
+
+		/**
+		 * Specify the reference to the {@link Field field} holding the regular expression to apply.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 */
+		public RegexFindAll regexOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "fieldReference must not be null!");
+
+			return new RegexFindAll(append("regex", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Specify the {@link AggregationExpression} evaluating to the regular expression to apply.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexFindAll}.
+		 */
+		public RegexFindAll regexOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+
+			return new RegexFindAll(append("regex", expression));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$regexFindAll";
+		}
+	}
+
+	/**
+	 * {@link AggregationExpression} for {@code $regexMatch} which applies a regular expression (regex) to a string and
+	 * returns a boolean that indicates if a match is found or not. <br />
+	 * <strong>NOTE:</strong> Requires MongoDB 4.0 or later.
+	 *
+	 * @author Divya Srivastava
+	 * @since 3.3
+	 */
+	public static class RegexMatch extends AbstractAggregationExpression {
+
+		protected RegexMatch(Object value) {
+			super(value);
+		}
+
+		/**
+		 * Creates new {@link RegexMatch} using the value of the provided {@link Field fieldReference} as {@literal input}
+		 * value.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 */
+		public static RegexMatch valueOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+
+			return new RegexMatch(Collections.singletonMap("input", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Creates new {@link RegexMatch} using the result of the provided {@link AggregationExpression} as {@literal input}
+		 * value.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 */
+		public static RegexMatch valueOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+
+			return new RegexMatch(Collections.singletonMap("input", expression));
+		}
+
+		/**
+		 * Optional specify the options to use with the regular expression.
+		 *
+		 * @param options must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 */
+		public RegexMatch options(String options) {
+
+			Assert.notNull(options, "Options must not be null!");
+
+			return new RegexMatch(append("options", options));
+		}
+
+		/**
+		 * Optional specify the reference to the {@link Field field} holding the options values to use with the regular
+		 * expression.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 */
+		public RegexMatch optionsOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+
+			return new RegexMatch(append("options", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Optional specify the {@link AggregationExpression} evaluating to the options values to use with the regular
+		 * expression.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 */
+		public RegexMatch optionsOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+
+			return new RegexMatch(append("options", expression));
+		}
+
+		/**
+		 * Apply a {@link Pattern} into {@code regex} and {@code options} fields.
+		 *
+		 * @param pattern must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 */
+		public RegexMatch pattern(Pattern pattern) {
+
+			Assert.notNull(pattern, "Pattern must not be null!");
+
+			Map<String, Object> regex = append("regex", pattern.pattern());
+			regex.put("options", RegexFlags.toRegexOptions(pattern.flags()));
+
+			return new RegexMatch(regex);
+		}
+
+		/**
+		 * Specify the regular expression to apply.
+		 *
+		 * @param regex must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 */
+		public RegexMatch regex(String regex) {
+
+			Assert.notNull(regex, "Regex must not be null!");
+
+			return new RegexMatch(append("regex", regex));
+		}
+
+		/**
+		 * Specify the reference to the {@link Field field} holding the regular expression to apply.
+		 *
+		 * @param fieldReference must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 */
+		public RegexMatch regexOf(String fieldReference) {
+
+			Assert.notNull(fieldReference, "FieldReference must not be null!");
+
+			return new RegexMatch(append("regex", Fields.field(fieldReference)));
+		}
+
+		/**
+		 * Optional specify the {@link AggregationExpression} evaluating to the regular expression to apply.
+		 *
+		 * @param expression must not be {@literal null}.
+		 * @return new instance of {@link RegexMatch}.
+		 */
+		public RegexMatch regexOf(AggregationExpression expression) {
+
+			Assert.notNull(expression, "Expression must not be null!");
+
+			return new RegexMatch(append("regex", expression));
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$regexMatch";
+		}
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/TypeBasedAggregationOperationContext.java

@@ -166,4 +166,8 @@ public class TypeBasedAggregationOperationContext implements AggregationOperatio
 
 		return new DirectFieldReference(new ExposedField(mappedField, true));
 	}
+
+	public Class<?> getType() {
+		return type;
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/UnionWithOperation.java

@@ -28,7 +28,7 @@ import org.springframework.util.Assert;
  * containing duplicates, into a single result set that is handed over to the next stage. <br />
  * In order to remove duplicates it is possible to append a {@link GroupOperation} right after
  * {@link UnionWithOperation}.
- * <p />
+ * <br />
  * If the {@link UnionWithOperation} uses a
  * <a href="https://docs.mongodb.com/master/reference/operator/aggregation/unionWith/#unionwith-pipeline">pipeline</a>
  * to process documents, field names within the pipeline will be treated as is. In order to map domain type property

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/DbRefResolver.java

@@ -35,7 +35,7 @@ import com.mongodb.DBRef;
  * @author Mark Paluch
  * @since 1.4
  */
-public interface DbRefResolver {
+public interface DbRefResolver extends ReferenceResolver {
 
 	/**
 	 * Resolves the given {@link DBRef} into an object of the given {@link MongoPersistentProperty}'s type. The method

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/DefaultDbRefResolver.java

@@ -15,13 +15,6 @@
  */
 package org.springframework.data.mongodb.core.convert;
 
-import static org.springframework.util.ReflectionUtils.*;
-
-import java.io.IOException;
-import java.io.ObjectInputStream;
-import java.io.ObjectOutputStream;
-import java.io.Serializable;
-import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -29,28 +22,18 @@ import java.util.List;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
-import org.aopalliance.intercept.MethodInterceptor;
-import org.aopalliance.intercept.MethodInvocation;
 import org.bson.Document;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-import org.springframework.aop.framework.ProxyFactory;
-import org.springframework.cglib.proxy.Callback;
-import org.springframework.cglib.proxy.Enhancer;
-import org.springframework.cglib.proxy.Factory;
-import org.springframework.cglib.proxy.MethodProxy;
-import org.springframework.dao.DataAccessException;
+
 import org.springframework.dao.InvalidDataAccessApiUsageException;
-import org.springframework.dao.support.PersistenceExceptionTranslator;
-import org.springframework.data.mongodb.ClientSessionException;
-import org.springframework.data.mongodb.LazyLoadingException;
 import org.springframework.data.mongodb.MongoDatabaseFactory;
 import org.springframework.data.mongodb.MongoDatabaseUtils;
+import org.springframework.data.mongodb.core.convert.ReferenceLoader.DocumentReferenceQuery;
+import org.springframework.data.mongodb.core.mapping.BasicMongoPersistentProperty;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.lang.Nullable;
-import org.springframework.objenesis.ObjenesisStd;
 import org.springframework.util.Assert;
-import org.springframework.util.ReflectionUtils;
 import org.springframework.util.StringUtils;
 
 import com.mongodb.DBRef;
@@ -67,13 +50,11 @@ import com.mongodb.client.model.Filters;
  * @author Mark Paluch
  * @since 1.4
  */
-public class DefaultDbRefResolver implements DbRefResolver {
+public class DefaultDbRefResolver extends DefaultReferenceResolver implements DbRefResolver, ReferenceResolver {
 
 	private static final Logger LOGGER = LoggerFactory.getLogger(DefaultDbRefResolver.class);
 
 	private final MongoDatabaseFactory mongoDbFactory;
-	private final PersistenceExceptionTranslator exceptionTranslator;
-	private final ObjenesisStd objenesis;
 
 	/**
 	 * Creates a new {@link DefaultDbRefResolver} with the given {@link MongoDatabaseFactory}.
@@ -82,11 +63,11 @@ public class DefaultDbRefResolver implements DbRefResolver {
 	 */
 	public DefaultDbRefResolver(MongoDatabaseFactory mongoDbFactory) {
 
+		super(new MongoDatabaseFactoryReferenceLoader(mongoDbFactory), mongoDbFactory.getExceptionTranslator());
+
 		Assert.notNull(mongoDbFactory, "MongoDbFactory translator must not be null!");
 
 		this.mongoDbFactory = mongoDbFactory;
-		this.exceptionTranslator = mongoDbFactory.getExceptionTranslator();
-		this.objenesis = new ObjenesisStd(true);
 	}
 
 	/*
@@ -114,17 +95,8 @@ public class DefaultDbRefResolver implements DbRefResolver {
 	 */
 	@Override
 	public Document fetch(DBRef dbRef) {
-
-		MongoCollection<Document> mongoCollection = getCollection(dbRef);
-
-		if (LOGGER.isTraceEnabled()) {
-			LOGGER.trace("Fetching DBRef '{}' from {}.{}.", dbRef.getId(),
-					StringUtils.hasText(dbRef.getDatabaseName()) ? dbRef.getDatabaseName()
-							: mongoCollection.getNamespace().getDatabaseName(),
-					dbRef.getCollectionName());
-		}
-
-		return mongoCollection.find(Filters.eq("_id", dbRef.getId())).first();
+		return getReferenceLoader().fetchOne(DocumentReferenceQuery.forSingleDocument(Filters.eq("_id", dbRef.getId())),
+				ReferenceCollection.fromDBRef(dbRef));
 	}
 
 	/*
@@ -165,7 +137,7 @@ public class DefaultDbRefResolver implements DbRefResolver {
 		}
 
 		List<Document> result = mongoCollection //
-				.find(new Document("_id", new Document("$in", ids))) //
+				.find(new Document(BasicMongoPersistentProperty.ID_FIELD_NAME, new Document("$in", ids))) //
 				.into(new ArrayList<>());
 
 		return ids.stream() //
@@ -185,44 +157,9 @@ public class DefaultDbRefResolver implements DbRefResolver {
 	private Object createLazyLoadingProxy(MongoPersistentProperty property, @Nullable DBRef dbref,
 			DbRefResolverCallback callback, DbRefProxyHandler handler) {
 
-		Class<?> propertyType = property.getType();
-		LazyLoadingInterceptor interceptor = new LazyLoadingInterceptor(property, dbref, exceptionTranslator, callback);
+		Object lazyLoadingProxy = getProxyFactory().createLazyLoadingProxy(property, callback, dbref);
 
-		if (!propertyType.isInterface()) {
-
-			Factory factory = (Factory) objenesis.newInstance(getEnhancedTypeFor(propertyType));
-			factory.setCallbacks(new Callback[] { interceptor });
-
-			return handler.populateId(property, dbref, factory);
-		}
-
-		ProxyFactory proxyFactory = new ProxyFactory();
-
-		for (Class<?> type : propertyType.getInterfaces()) {
-			proxyFactory.addInterface(type);
-		}
-
-		proxyFactory.addInterface(LazyLoadingProxy.class);
-		proxyFactory.addInterface(propertyType);
-		proxyFactory.addAdvice(interceptor);
-
-		return handler.populateId(property, dbref, proxyFactory.getProxy(LazyLoadingProxy.class.getClassLoader()));
-	}
-
-	/**
-	 * Returns the CGLib enhanced type for the given source type.
-	 *
-	 * @param type
-	 * @return
-	 */
-	private Class<?> getEnhancedTypeFor(Class<?> type) {
-
-		Enhancer enhancer = new Enhancer();
-		enhancer.setSuperclass(type);
-		enhancer.setCallbackType(org.springframework.cglib.proxy.MethodInterceptor.class);
-		enhancer.setInterfaces(new Class[] { LazyLoadingProxy.class });
-
-		return enhancer.createClass();
+		return handler.populateId(property, dbref, lazyLoadingProxy);
 	}
 
 	/**
@@ -245,253 +182,10 @@ public class DefaultDbRefResolver implements DbRefResolver {
 	private static Stream<Document> documentWithId(Object identifier, Collection<Document> documents) {
 
 		return documents.stream() //
-				.filter(it -> it.get("_id").equals(identifier)) //
+				.filter(it -> it.get(BasicMongoPersistentProperty.ID_FIELD_NAME).equals(identifier)) //
 				.limit(1);
 	}
 
-	/**
-	 * A {@link MethodInterceptor} that is used within a lazy loading proxy. The property resolving is delegated to a
-	 * {@link DbRefResolverCallback}. The resolving process is triggered by a method invocation on the proxy and is
-	 * guaranteed to be performed only once.
-	 *
-	 * @author Thomas Darimont
-	 * @author Oliver Gierke
-	 * @author Christoph Strobl
-	 */
-	static class LazyLoadingInterceptor
-			implements MethodInterceptor, org.springframework.cglib.proxy.MethodInterceptor, Serializable {
-
-		private static final Method INITIALIZE_METHOD, TO_DBREF_METHOD, FINALIZE_METHOD;
-
-		private final DbRefResolverCallback callback;
-		private final MongoPersistentProperty property;
-		private final PersistenceExceptionTranslator exceptionTranslator;
-
-		private volatile boolean resolved;
-		private final @Nullable DBRef dbref;
-		private @Nullable Object result;
-
-		static {
-			try {
-				INITIALIZE_METHOD = LazyLoadingProxy.class.getMethod("getTarget");
-				TO_DBREF_METHOD = LazyLoadingProxy.class.getMethod("toDBRef");
-				FINALIZE_METHOD = Object.class.getDeclaredMethod("finalize");
-			} catch (Exception e) {
-				throw new RuntimeException(e);
-			}
-		}
-
-		/**
-		 * Creates a new {@link LazyLoadingInterceptor} for the given {@link MongoPersistentProperty},
-		 * {@link PersistenceExceptionTranslator} and {@link DbRefResolverCallback}.
-		 *
-		 * @param property must not be {@literal null}.
-		 * @param dbref can be {@literal null}.
-		 * @param callback must not be {@literal null}.
-		 */
-		public LazyLoadingInterceptor(MongoPersistentProperty property, @Nullable DBRef dbref,
-				PersistenceExceptionTranslator exceptionTranslator, DbRefResolverCallback callback) {
-
-			Assert.notNull(property, "Property must not be null!");
-			Assert.notNull(exceptionTranslator, "Exception translator must not be null!");
-			Assert.notNull(callback, "Callback must not be null!");
-
-			this.dbref = dbref;
-			this.callback = callback;
-			this.exceptionTranslator = exceptionTranslator;
-			this.property = property;
-		}
-
-		/*
-		 * (non-Javadoc)
-		 * @see org.aopalliance.intercept.MethodInterceptor#invoke(org.aopalliance.intercept.MethodInvocation)
-		 */
-		@Override
-		public Object invoke(@Nullable MethodInvocation invocation) throws Throwable {
-			return intercept(invocation.getThis(), invocation.getMethod(), invocation.getArguments(), null);
-		}
-
-		/*
-		 * (non-Javadoc)
-		 * @see org.springframework.cglib.proxy.MethodInterceptor#intercept(java.lang.Object, java.lang.reflect.Method, java.lang.Object[], org.springframework.cglib.proxy.MethodProxy)
-		 */
-		@Nullable
-		@Override
-		public Object intercept(Object obj, Method method, Object[] args, @Nullable MethodProxy proxy) throws Throwable {
-
-			if (INITIALIZE_METHOD.equals(method)) {
-				return ensureResolved();
-			}
-
-			if (TO_DBREF_METHOD.equals(method)) {
-				return this.dbref;
-			}
-
-			if (isObjectMethod(method) && Object.class.equals(method.getDeclaringClass())) {
-
-				if (ReflectionUtils.isToStringMethod(method)) {
-					return proxyToString(proxy);
-				}
-
-				if (ReflectionUtils.isEqualsMethod(method)) {
-					return proxyEquals(proxy, args[0]);
-				}
-
-				if (ReflectionUtils.isHashCodeMethod(method)) {
-					return proxyHashCode(proxy);
-				}
-
-				// DATAMONGO-1076 - finalize methods should not trigger proxy initialization
-				if (FINALIZE_METHOD.equals(method)) {
-					return null;
-				}
-			}
-
-			Object target = ensureResolved();
-
-			if (target == null) {
-				return null;
-			}
-
-			ReflectionUtils.makeAccessible(method);
-
-			return method.invoke(target, args);
-		}
-
-		/**
-		 * Returns a to string representation for the given {@code proxy}.
-		 *
-		 * @param proxy
-		 * @return
-		 */
-		private String proxyToString(@Nullable Object proxy) {
-
-			StringBuilder description = new StringBuilder();
-			if (dbref != null) {
-				description.append(dbref.getCollectionName());
-				description.append(":");
-				description.append(dbref.getId());
-			} else {
-				description.append(System.identityHashCode(proxy));
-			}
-			description.append("$").append(LazyLoadingProxy.class.getSimpleName());
-
-			return description.toString();
-		}
-
-		/**
-		 * Returns the hashcode for the given {@code proxy}.
-		 *
-		 * @param proxy
-		 * @return
-		 */
-		private int proxyHashCode(@Nullable Object proxy) {
-			return proxyToString(proxy).hashCode();
-		}
-
-		/**
-		 * Performs an equality check for the given {@code proxy}.
-		 *
-		 * @param proxy
-		 * @param that
-		 * @return
-		 */
-		private boolean proxyEquals(@Nullable Object proxy, Object that) {
-
-			if (!(that instanceof LazyLoadingProxy)) {
-				return false;
-			}
-
-			if (that == proxy) {
-				return true;
-			}
-
-			return proxyToString(proxy).equals(that.toString());
-		}
-
-		/**
-		 * Will trigger the resolution if the proxy is not resolved already or return a previously resolved result.
-		 *
-		 * @return
-		 */
-		@Nullable
-		private Object ensureResolved() {
-
-			if (!resolved) {
-				this.result = resolve();
-				this.resolved = true;
-			}
-
-			return this.result;
-		}
-
-		/**
-		 * Callback method for serialization.
-		 *
-		 * @param out
-		 * @throws IOException
-		 */
-		private void writeObject(ObjectOutputStream out) throws IOException {
-
-			ensureResolved();
-			out.writeObject(this.result);
-		}
-
-		/**
-		 * Callback method for deserialization.
-		 *
-		 * @param in
-		 * @throws IOException
-		 */
-		private void readObject(ObjectInputStream in) throws IOException {
-
-			try {
-				this.resolved = true;
-				this.result = in.readObject();
-			} catch (ClassNotFoundException e) {
-				throw new LazyLoadingException("Could not deserialize result", e);
-			}
-		}
-
-		/**
-		 * Resolves the proxy into its backing object.
-		 *
-		 * @return
-		 */
-		@Nullable
-		private synchronized Object resolve() {
-
-			if (resolved) {
-
-				if (LOGGER.isTraceEnabled()) {
-					LOGGER.trace("Accessing already resolved lazy loading property {}.{}",
-							property.getOwner() != null ? property.getOwner().getName() : "unknown", property.getName());
-				}
-				return result;
-			}
-
-			try {
-				if (LOGGER.isTraceEnabled()) {
-					LOGGER.trace("Resolving lazy loading property {}.{}",
-							property.getOwner() != null ? property.getOwner().getName() : "unknown", property.getName());
-				}
-
-				return callback.resolve(property);
-
-			} catch (RuntimeException ex) {
-
-				DataAccessException translatedException = this.exceptionTranslator.translateExceptionIfPossible(ex);
-
-				if (translatedException instanceof ClientSessionException) {
-					throw new LazyLoadingException("Unable to lazily resolve DBRef! Invalid session state.", ex);
-				}
-
-				throw new LazyLoadingException("Unable to lazily resolve DBRef!",
-						translatedException != null ? translatedException : ex);
-			}
-		}
-	}
-
 	/**
 	 * Customization hook for obtaining the {@link MongoCollection} for a given {@link DBRef}.
 	 *
@@ -504,4 +198,10 @@ public class DefaultDbRefResolver implements DbRefResolver {
 		return MongoDatabaseUtils.getDatabase(dbref.getDatabaseName(), mongoDbFactory)
 				.getCollection(dbref.getCollectionName(), Document.class);
 	}
+
+	protected MongoCollection<Document> getCollection(ReferenceCollection context) {
+
+		return MongoDatabaseUtils.getDatabase(context.getDatabase(), mongoDbFactory).getCollection(context.getCollection(),
+				Document.class);
+	}
 }

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/DefaultReferenceResolver.java

@@ -0,0 +1,113 @@
+/*
+ * Copyright 2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.mongodb.core.convert;
+
+import static org.springframework.data.mongodb.core.convert.ReferenceLookupDelegate.*;
+
+import java.util.Collections;
+
+import org.springframework.dao.support.PersistenceExceptionTranslator;
+import org.springframework.data.mongodb.core.mapping.DBRef;
+import org.springframework.data.mongodb.core.mapping.DocumentReference;
+import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
+import org.springframework.util.Assert;
+
+/**
+ * {@link ReferenceResolver} implementation that uses a given {@link ReferenceLookupDelegate} to load and convert entity
+ * associations expressed via a {@link MongoPersistentProperty persitent property}. Creates {@link LazyLoadingProxy
+ * proxies} for associations that should be lazily loaded.
+ *
+ * @author Christoph Strobl
+ * @author Mark Paluch
+ * @since 3.3
+ */
+public class DefaultReferenceResolver implements ReferenceResolver {
+
+	private final ReferenceLoader referenceLoader;
+	private final LazyLoadingProxyFactory proxyFactory;
+
+	private final LookupFunction collectionLookupFunction = (filter, ctx) -> getReferenceLoader().fetchMany(filter, ctx);
+	private final LookupFunction singleValueLookupFunction = (filter, ctx) -> {
+		Object target = getReferenceLoader().fetchOne(filter, ctx);
+		return target == null ? Collections.emptyList() : Collections.singleton(getReferenceLoader().fetchOne(filter, ctx));
+	};
+
+	/**
+	 * Create a new instance of {@link DefaultReferenceResolver}.
+	 *
+	 * @param referenceLoader must not be {@literal null}.
+	 * @param exceptionTranslator must not be {@literal null}.
+	 */
+	public DefaultReferenceResolver(ReferenceLoader referenceLoader, PersistenceExceptionTranslator exceptionTranslator) {
+
+		Assert.notNull(referenceLoader, "ReferenceLoader must not be null!");
+		Assert.notNull(exceptionTranslator, "ExceptionTranslator must not be null!");
+
+		this.referenceLoader = referenceLoader;
+		this.proxyFactory = new LazyLoadingProxyFactory(exceptionTranslator);
+	}
+
+	@Override
+	public Object resolveReference(MongoPersistentProperty property, Object source,
+			ReferenceLookupDelegate referenceLookupDelegate, MongoEntityReader entityReader) {
+
+		LookupFunction lookupFunction = (property.isCollectionLike() || property.isMap()) ? collectionLookupFunction
+				: singleValueLookupFunction;
+
+		if (isLazyReference(property)) {
+			return createLazyLoadingProxy(property, source, referenceLookupDelegate, lookupFunction, entityReader);
+		}
+
+		return referenceLookupDelegate.readReference(property, source, lookupFunction, entityReader);
+	}
+
+	/**
+	 * Check if the association expressed by the given {@link MongoPersistentProperty property} should be resolved lazily.
+	 *
+	 * @param property
+	 * @return return {@literal true} if the defined association is lazy.
+	 * @see DBRef#lazy()
+	 * @see DocumentReference#lazy()
+	 */
+	protected boolean isLazyReference(MongoPersistentProperty property) {
+
+		if (property.isDocumentReference()) {
+			return property.getDocumentReference().lazy();
+		}
+
+		return property.getDBRef() != null && property.getDBRef().lazy();
+	}
+
+	/**
+	 * The {@link ReferenceLoader} executing the lookup.
+	 *
+	 * @return never {@literal null}.
+	 */
+	protected ReferenceLoader getReferenceLoader() {
+		return referenceLoader;
+	}
+
+	LazyLoadingProxyFactory getProxyFactory() {
+		return proxyFactory;
+	}
+
+	private Object createLazyLoadingProxy(MongoPersistentProperty property, Object source,
+			ReferenceLookupDelegate referenceLookupDelegate, LookupFunction lookupFunction, MongoEntityReader entityReader) {
+		return proxyFactory.createLazyLoadingProxy(property, it -> {
+			return referenceLookupDelegate.readReference(it, source, lookupFunction, entityReader);
+		}, source instanceof DocumentReferenceSource ? ((DocumentReferenceSource)source).getTargetSource() : source);
+	}
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/DocumentAccessor.java

@@ -21,13 +21,13 @@ import java.util.Map;
 
 import org.bson.Document;
 import org.bson.conversions.Bson;
+
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.data.mongodb.util.BsonUtils;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
-import com.mongodb.BasicDBObject;
 import com.mongodb.DBObject;
 
 /**
@@ -67,6 +67,19 @@ class DocumentAccessor {
 		return this.document;
 	}
 
+	/**
+	 * Copies all of the mappings from the given {@link Document} to the underlying target {@link Document}. These
+	 * mappings will replace any mappings that the target document had for any of the keys currently in the specified map.
+	 *
+	 * @param source
+	 */
+	public void putAll(Document source) {
+
+		Map<String, Object> target = BsonUtils.asMap(document);
+
+		target.putAll(source);
+	}
+
 	/**
 	 * Puts the given value into the backing {@link Document} based on the coordinates defined through the given
 	 * {@link MongoPersistentProperty}. By default this will be the plain field name. But field names might also consist
@@ -110,28 +123,7 @@ class DocumentAccessor {
 	 */
 	@Nullable
 	public Object get(MongoPersistentProperty property) {
-
-		String fieldName = property.getFieldName();
-		Map<String, Object> map = BsonUtils.asMap(document);
-
-		if (!fieldName.contains(".")) {
-			return map.get(fieldName);
-		}
-
-		Iterator<String> parts = Arrays.asList(fieldName.split("\\.")).iterator();
-		Map<String, Object> source = map;
-		Object result = null;
-
-		while (source != null && parts.hasNext()) {
-
-			result = source.get(parts.next());
-
-			if (parts.hasNext()) {
-				source = getAsMap(result);
-			}
-		}
-
-		return result;
+		return BsonUtils.resolveValue(document, property.getFieldName());
 	}
 
 	/**
@@ -141,8 +133,9 @@ class DocumentAccessor {
 	 * @param entity must not be {@literal null}.
 	 * @return
 	 */
+	@Nullable
 	public Object getRawId(MongoPersistentEntity<?> entity) {
-		return entity.hasIdProperty() ? get(entity.getRequiredIdProperty()) : BsonUtils.asMap(document).get("_id");
+		return entity.hasIdProperty() ? get(entity.getRequiredIdProperty()) : BsonUtils.get(document, "_id");
 	}
 
 	/**
@@ -157,71 +150,7 @@ class DocumentAccessor {
 
 		Assert.notNull(property, "Property must not be null!");
 
-		String fieldName = property.getFieldName();
-
-
-		if (this.document instanceof Document) {
-
-			if (((Document) this.document).containsKey(fieldName)) {
-				return true;
-			}
-		} else if (this.document instanceof DBObject) {
-			if (((DBObject) this.document).containsField(fieldName)) {
-				return true;
-			}
-		}
-
-		if (!fieldName.contains(".")) {
-			return false;
-		}
-
-		String[] parts = fieldName.split("\\.");
-		Map<String, Object> source;
-
-		if (this.document instanceof Document) {
-			source = ((Document) this.document);
-		} else {
-			source = ((DBObject) this.document).toMap();
-		}
-
-		Object result = null;
-
-		for (int i = 1; i < parts.length; i++) {
-
-			result = source.get(parts[i - 1]);
-			source = getAsMap(result);
-
-			if (source == null) {
-				return false;
-			}
-		}
-
-		return source.containsKey(parts[parts.length - 1]);
-	}
-
-	/**
-	 * Returns the given source object as map, i.e. {@link Document}s and maps as is or {@literal null} otherwise.
-	 *
-	 * @param source can be {@literal null}.
-	 * @return can be {@literal null}.
-	 */
-	@Nullable
-	@SuppressWarnings("unchecked")
-	private static Map<String, Object> getAsMap(Object source) {
-
-		if (source instanceof Document) {
-			return (Document) source;
-		}
-
-		if (source instanceof BasicDBObject) {
-			return (BasicDBObject) source;
-		}
-
-		if (source instanceof Map) {
-			return (Map<String, Object>) source;
-		}
-
-		return null;
+		return BsonUtils.hasValue(document, property.getFieldName());
 	}
 
 	/**