Release version 3.2.1 (2021.0.1).

See #3629

.github/PULL_REQUEST_TEMPLATE.md

@@ -6,7 +6,6 @@ Make sure that:
 -->
 
 - [ ] You have read the [Spring Data contribution guidelines](https://github.com/spring-projects/spring-data-build/blob/master/CONTRIBUTING.adoc).
-- [ ] There is a ticket in the bug tracker for the project in our [JIRA](https://jira.spring.io/browse/DATAMONGO).
 - [ ] You use the code formatters provided [here](https://github.com/spring-projects/spring-data-build/tree/master/etc/ide) and have them applied to your changes. Don’t submit any formatting related changes.
 - [ ] You submit test cases (unit or integration tests) that back your changes.
 - [ ] You added yourself as author in the headers of the classes you touched. Amend the date range in the Apache license header if needed. For new types, add the license header (copy from another file and set the current year only).

.github/workflows/project.yml

@@ -0,0 +1,47 @@
+# GitHub Actions to automate GitHub issues for Spring Data Project Management
+
+name: Spring Data GitHub Issues
+
+on:
+  issues:
+    types: [opened, edited, reopened]
+  issue_comment:
+    types: [created]
+  pull_request_target:
+    types: [opened, edited, reopened]
+
+jobs:
+  Inbox:
+    runs-on: ubuntu-latest
+    if: github.repository_owner == 'spring-projects' && (github.event.action == 'opened' || github.event.action == 'reopened') && github.event.pull_request == null
+    steps:
+      - name: Create or Update Issue Card
+        uses: peter-evans/create-or-update-project-card@v1.1.2
+        with:
+          project-name: 'Spring Data'
+          column-name: 'Inbox'
+          project-location: 'spring-projects'
+          token: ${{ secrets.GH_ISSUES_TOKEN_SPRING_DATA }}
+  Pull-Request:
+    runs-on: ubuntu-latest
+    if: github.repository_owner == 'spring-projects' && (github.event.action == 'opened' || github.event.action == 'reopened') && github.event.pull_request != null
+    steps:
+      - name: Create or Update Pull Request Card
+        uses: peter-evans/create-or-update-project-card@v1.1.2
+        with:
+          project-name: 'Spring Data'
+          column-name: 'Review pending'
+          project-location: 'spring-projects'
+          issue-number: ${{ github.event.pull_request.number }}
+          token: ${{ secrets.GH_ISSUES_TOKEN_SPRING_DATA }}
+  Feedback-Provided:
+    runs-on: ubuntu-latest
+    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
+        with:
+          project-name: 'Spring Data'
+          column-name: 'Feedback provided'
+          project-location: 'spring-projects'
+          token: ${{ secrets.GH_ISSUES_TOKEN_SPRING_DATA }}

CODE_OF_CONDUCT.adoc

@@ -1,27 +0,0 @@
-= Contributor Code of Conduct
-
-As contributors and maintainers of this project, and in the interest of fostering an open and welcoming community, we pledge to respect all people who contribute through reporting issues, posting feature requests, updating documentation, submitting pull requests or patches, and other activities.
-
-We are committed to making participation in this project a harassment-free experience for everyone, regardless of level of experience, gender, gender identity and expression, sexual orientation, disability, personal appearance, body size, race, ethnicity, age, religion, or nationality.
-
-Examples of unacceptable behavior by participants include:
-
-* The use of sexualized language or imagery
-* Personal attacks
-* Trolling or insulting/derogatory comments
-* Public or private harassment
-* Publishing other's private information, such as physical or electronic addresses,
-  without explicit permission
-* Other unethical or unprofessional conduct
-
-Project maintainers have the right and responsibility to remove, edit, or reject comments, commits, code, wiki edits, issues, and other contributions that are not aligned to this Code of Conduct, or to ban temporarily or permanently any contributor for other behaviors that they deem inappropriate, threatening, offensive, or harmful.
-
-By adopting this Code of Conduct, project maintainers commit themselves to fairly and consistently applying these principles to every aspect of managing this project. Project maintainers who do not follow or enforce the Code of Conduct may be permanently removed from the project team.
-
-This Code of Conduct applies both within project spaces and in public spaces when an individual is representing the project or its community.
-
-Instances of abusive, harassing, or otherwise unacceptable behavior may be reported by contacting a project maintainer at spring-code-of-conduct@pivotal.io.
-All complaints will be reviewed and investigated and will result in a response that is deemed necessary and appropriate to the circumstances.
-Maintainers are obligated to maintain confidentiality with regard to the reporter of an incident.
-
-This Code of Conduct is adapted from the https://contributor-covenant.org[Contributor Covenant], version 1.3.0, available at https://contributor-covenant.org/version/1/3/0/[contributor-covenant.org/version/1/3/0/].

Jenkinsfile

@@ -3,7 +3,7 @@ pipeline {
 
 	triggers {
 		pollSCM 'H/10 * * * *'
-		upstream(upstreamProjects: "spring-data-commons/2.3.x", threshold: hudson.model.Result.SUCCESS)
+		upstream(upstreamProjects: "spring-data-commons/2.5.x", threshold: hudson.model.Result.SUCCESS)
 	}
 
 	options {
@@ -23,39 +23,39 @@ 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 14 + MongoDB 4.2') {
+				stage('Publish JDK 15 + MongoDB 4.4') {
 					when {
-						changeset "ci/openjdk14-mongodb-4.2/**"
+						changeset "ci/openjdk15-mongodb-4.4/**"
 					}
 					agent { label 'data' }
 					options { timeout(time: 30, unit: 'MINUTES') }
 
 					steps {
 						script {
-							def image = docker.build("springci/spring-data-openjdk14-with-mongodb-4.2.0", "ci/openjdk14-mongodb-4.2/")
+							def image = docker.build("springci/spring-data-openjdk15-with-mongodb-4.4.4", "ci/openjdk15-mongodb-4.4/")
 							docker.withRegistry('', 'hub.docker.com-springbuildmaster') {
 								image.push()
 							}
@@ -68,7 +68,7 @@ pipeline {
 		stage("test: baseline (jdk8)") {
 			when {
 				anyOf {
-					branch '3.0.x'
+					branch '3.2.x'
 					not { triggeredBy 'UpstreamCause' }
 				}
 			}
@@ -82,7 +82,7 @@ pipeline {
 			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'
@@ -97,8 +97,8 @@ pipeline {
 
 		stage("Test other configurations") {
 			when {
-				anyOf {
-					branch '3.0.x'
+				allOf {
+					branch '3.2.x'
 					not { triggeredBy 'UpstreamCause' }
 				}
 			}
@@ -114,7 +114,7 @@ pipeline {
 					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'
@@ -127,7 +127,7 @@ pipeline {
 					}
 				}
 
-				stage("test: mongodb 4.2 (jdk8)") {
+				stage("test: mongodb 4.4 (jdk8)") {
 					agent {
 						label 'data'
 					}
@@ -138,7 +138,7 @@ pipeline {
 					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'
@@ -151,7 +151,7 @@ pipeline {
 					}
 				}
 
-				stage("test: baseline (jdk14)") {
+				stage("test: baseline (jdk15)") {
 					agent {
 						label 'data'
 					}
@@ -162,7 +162,7 @@ pipeline {
 					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-openjdk15-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'
@@ -180,7 +180,7 @@ pipeline {
 		stage('Release to artifactory') {
 			when {
 				anyOf {
-					branch '3.0.x'
+					branch '3.2.x'
 					not { triggeredBy 'UpstreamCause' }
 				}
 			}
@@ -213,7 +213,7 @@ pipeline {
 
 		stage('Publish documentation') {
 			when {
-				branch '3.0.x'
+				branch '3.2.x'
 			}
 			agent {
 				label 'data'

README.adoc

@@ -10,7 +10,7 @@ Key functional areas of Spring Data MongoDB are a POJO centric model for interac
 
 == Code of Conduct
 
-This project is governed by the link:CODE_OF_CONDUCT.adoc[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.
+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
 

ci/openjdk11-mongodb-4.4/Dockerfile

@@ -5,11 +5,11 @@ 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; \
+	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=4.2.0 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 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-4.4/Dockerfile

@@ -1,15 +1,15 @@
-FROM adoptopenjdk/openjdk14:latest
+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; \
+	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=4.2.0 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 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

@@ -10,6 +10,6 @@ RUN RUN set -eux; \
 	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-4.4/Dockerfile

@@ -5,11 +5,13 @@ 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; \
+	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=4.2.0 mongodb-org-server=4.2.0 mongodb-org-shell=4.2.0 mongodb-org-mongos=4.2.0 mongodb-org-tools=4.2.0 ; \
+	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/*;

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-mongodb-parent</artifactId>
-	<version>3.0.10.BUILD-SNAPSHOT</version>
+	<version>3.2.1</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>2.3.10.BUILD-SNAPSHOT</version>
+		<version>2.5.1</version>
 	</parent>
 
 	<modules>
@@ -26,8 +26,8 @@
 	<properties>
 		<project.type>multi</project.type>
 		<dist.id>spring-data-mongodb</dist.id>
-		<springdata.commons>2.3.10.BUILD-SNAPSHOT</springdata.commons>
-		<mongo>4.0.6</mongo>
+		<springdata.commons>2.5.1</springdata.commons>
+		<mongo>4.2.3</mongo>
 		<mongo.reactivestreams>${mongo}</mongo.reactivestreams>
 		<jmh.version>1.19</jmh.version>
 	</properties>
@@ -134,8 +134,8 @@
 
 	<repositories>
 		<repository>
-			<id>spring-libs-snapshot</id>
-			<url>https://repo.spring.io/libs-snapshot</url>
+			<id>spring-libs-release</id>
+			<url>https://repo.spring.io/libs-release</url>
 		</repository>
 		<repository>
 			<id>sonatype-libs-snapshot</id>

spring-data-mongodb-benchmarks/pom.xml

@@ -7,7 +7,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>3.0.10.BUILD-SNAPSHOT</version>
+		<version>3.2.1</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>3.0.10.BUILD-SNAPSHOT</version>
+		<version>3.2.1</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>3.0.10.BUILD-SNAPSHOT</version>
+		<version>3.2.1</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 
@@ -136,6 +136,13 @@
 			<optional>true</optional>
 		</dependency>
 
+		<dependency>
+			<groupId>io.reactivex.rxjava3</groupId>
+			<artifactId>rxjava</artifactId>
+			<version>${rxjava3}</version>
+			<optional>true</optional>
+		</dependency>
+
 		<!-- CDI -->
 		<!-- Dependency order required to build against CDI 1.0 and test with CDI 2.0 -->
 		<dependency>
@@ -192,7 +199,14 @@
 		<dependency>
 			<groupId>org.hibernate</groupId>
 			<artifactId>hibernate-validator</artifactId>
-			<version>5.2.4.Final</version>
+			<version>5.4.3.Final</version>
+			<scope>test</scope>
+		</dependency>
+
+		<dependency>
+			<groupId>org.glassfish</groupId>
+			<artifactId>javax.el</artifactId>
+			<version>3.0.1-b11</version>
 			<scope>test</scope>
 		</dependency>
 

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()}.
+ * <p />
+ *
+ * <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/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.
+ * <p />
+ * 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/config/EnableMongoAuditing.java

@@ -61,8 +61,8 @@ public @interface EnableMongoAuditing {
 	boolean modifyOnCreate() default true;
 
 	/**
-	 * Configures a {@link DateTimeProvider} bean name that allows customizing the {@link org.joda.time.DateTime} to be
-	 * used for setting creation and modification dates.
+	 * Configures a {@link DateTimeProvider} bean name that allows customizing the timestamp to be used for setting
+	 * creation and modification dates.
 	 *
 	 * @return empty {@link String} by default.
 	 */

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

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2020-2021 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.config;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Inherited;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import org.springframework.context.annotation.Import;
+import org.springframework.data.auditing.DateTimeProvider;
+import org.springframework.data.domain.ReactiveAuditorAware;
+
+/**
+ * Annotation to enable auditing in MongoDB using reactive infrastructure via annotation configuration.
+ *
+ * @author Mark Paluch
+ * @since 3.1
+ */
+@Inherited
+@Documented
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+@Import(ReactiveMongoAuditingRegistrar.class)
+public @interface EnableReactiveMongoAuditing {
+
+	/**
+	 * Configures the {@link ReactiveAuditorAware} bean to be used to lookup the current principal.
+	 *
+	 * @return empty {@link String} by default.
+	 */
+	String auditorAwareRef() default "";
+
+	/**
+	 * Configures whether the creation and modification dates are set. Defaults to {@literal true}.
+	 *
+	 * @return {@literal true} by default.
+	 */
+	boolean setDates() default true;
+
+	/**
+	 * Configures whether the entity shall be marked as modified on creation. Defaults to {@literal true}.
+	 *
+	 * @return {@literal true} by default.
+	 */
+	boolean modifyOnCreate() default true;
+
+	/**
+	 * Configures a {@link DateTimeProvider} bean name that allows customizing the timestamp to be used for setting
+	 * creation and modification dates.
+	 *
+	 * @return empty {@link String} by default.
+	 */
+	String dateTimeProviderRef() default "";
+}

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

@@ -17,7 +17,6 @@ package org.springframework.data.mongodb.config;
 
 import java.lang.annotation.Annotation;
 
-import org.springframework.beans.factory.FactoryBean;
 import org.springframework.beans.factory.config.BeanDefinition;
 import org.springframework.beans.factory.support.AbstractBeanDefinition;
 import org.springframework.beans.factory.support.BeanDefinitionBuilder;
@@ -28,14 +27,8 @@ import org.springframework.data.auditing.IsNewAwareAuditingHandler;
 import org.springframework.data.auditing.config.AuditingBeanDefinitionRegistrarSupport;
 import org.springframework.data.auditing.config.AuditingConfiguration;
 import org.springframework.data.config.ParsingUtils;
-import org.springframework.data.mapping.context.MappingContext;
-import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
-import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
-import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.data.mongodb.core.mapping.event.AuditingEntityCallback;
-import org.springframework.data.mongodb.core.mapping.event.ReactiveAuditingEntityCallback;
 import org.springframework.util.Assert;
-import org.springframework.util.ClassUtils;
 
 /**
  * {@link ImportBeanDefinitionRegistrar} to enable {@link EnableMongoAuditing} annotation.
@@ -46,9 +39,6 @@ import org.springframework.util.ClassUtils;
  */
 class MongoAuditingRegistrar extends AuditingBeanDefinitionRegistrarSupport {
 
-	private static boolean PROJECT_REACTOR_AVAILABLE = ClassUtils.isPresent("reactor.core.publisher.Mono",
-			MongoAuditingRegistrar.class.getClassLoader());
-
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.auditing.config.AuditingBeanDefinitionRegistrarSupport#getAnnotation()
@@ -91,7 +81,7 @@ class MongoAuditingRegistrar extends AuditingBeanDefinitionRegistrarSupport {
 
 		BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(IsNewAwareAuditingHandler.class);
 
-		BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(MongoMappingContextLookup.class);
+		BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(PersistentEntitiesFactoryBean.class);
 		definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_CONSTRUCTOR);
 
 		builder.addConstructorArgValue(definition.getBeanDefinition());
@@ -116,68 +106,6 @@ class MongoAuditingRegistrar extends AuditingBeanDefinitionRegistrarSupport {
 
 		registerInfrastructureBeanWithId(listenerBeanDefinitionBuilder.getBeanDefinition(),
 				AuditingEntityCallback.class.getName(), registry);
-
-		if (PROJECT_REACTOR_AVAILABLE) {
-			registerReactiveAuditingEntityCallback(registry, auditingHandlerDefinition.getSource());
-		}
 	}
 
-	private void registerReactiveAuditingEntityCallback(BeanDefinitionRegistry registry, Object source) {
-
-		BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(ReactiveAuditingEntityCallback.class);
-
-		builder.addConstructorArgValue(ParsingUtils.getObjectFactoryBeanDefinition(getAuditingHandlerBeanName(), registry));
-		builder.getRawBeanDefinition().setSource(source);
-
-		registerInfrastructureBeanWithId(builder.getBeanDefinition(), ReactiveAuditingEntityCallback.class.getName(),
-				registry);
-	}
-
-	/**
-	 * Simple helper to be able to wire the {@link MappingContext} from a {@link MappingMongoConverter} bean available in
-	 * the application context.
-	 *
-	 * @author Oliver Gierke
-	 */
-	static class MongoMappingContextLookup
-			implements FactoryBean<MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty>> {
-
-		private final MappingMongoConverter converter;
-
-		/**
-		 * Creates a new {@link MongoMappingContextLookup} for the given {@link MappingMongoConverter}.
-		 *
-		 * @param converter must not be {@literal null}.
-		 */
-		public MongoMappingContextLookup(MappingMongoConverter converter) {
-			this.converter = converter;
-		}
-
-		/*
-		 * (non-Javadoc)
-		 * @see org.springframework.beans.factory.FactoryBean#getObject()
-		 */
-		@Override
-		public MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> getObject() throws Exception {
-			return converter.getMappingContext();
-		}
-
-		/*
-		 * (non-Javadoc)
-		 * @see org.springframework.beans.factory.FactoryBean#getObjectType()
-		 */
-		@Override
-		public Class<?> getObjectType() {
-			return MappingContext.class;
-		}
-
-		/*
-		 * (non-Javadoc)
-		 * @see org.springframework.beans.factory.FactoryBean#isSingleton()
-		 */
-		@Override
-		public boolean isSingleton() {
-			return true;
-		}
-	}
 }

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)) {
 

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

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2020-2021 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.config;
+
+import org.springframework.beans.factory.FactoryBean;
+import org.springframework.data.mapping.context.PersistentEntities;
+import org.springframework.data.mongodb.core.convert.MappingMongoConverter;
+
+/**
+ * Simple helper to be able to wire the {@link PersistentEntities} from a {@link MappingMongoConverter} bean available
+ * in the application context.
+ *
+ * @author Oliver Gierke
+ * @author Mark Paluch
+ * @author Christoph Strobl
+ * @since 3.1
+ */
+class PersistentEntitiesFactoryBean implements FactoryBean<PersistentEntities> {
+
+	private final MappingMongoConverter converter;
+
+	/**
+	 * Creates a new {@link PersistentEntitiesFactoryBean} for the given {@link MappingMongoConverter}.
+	 *
+	 * @param converter must not be {@literal null}.
+	 */
+	public PersistentEntitiesFactoryBean(MappingMongoConverter converter) {
+		this.converter = converter;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.beans.factory.FactoryBean#getObject()
+	 */
+	@Override
+	public PersistentEntities getObject() {
+		return PersistentEntities.of(converter.getMappingContext());
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.beans.factory.FactoryBean#getObjectType()
+	 */
+	@Override
+	public Class<?> getObjectType() {
+		return PersistentEntities.class;
+	}
+}

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

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2020-2021 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.config;
+
+import java.lang.annotation.Annotation;
+
+import org.springframework.beans.factory.config.BeanDefinition;
+import org.springframework.beans.factory.support.AbstractBeanDefinition;
+import org.springframework.beans.factory.support.BeanDefinitionBuilder;
+import org.springframework.beans.factory.support.BeanDefinitionRegistry;
+import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
+import org.springframework.core.type.AnnotationMetadata;
+import org.springframework.data.auditing.ReactiveIsNewAwareAuditingHandler;
+import org.springframework.data.auditing.config.AuditingBeanDefinitionRegistrarSupport;
+import org.springframework.data.auditing.config.AuditingConfiguration;
+import org.springframework.data.config.ParsingUtils;
+import org.springframework.data.mongodb.core.mapping.event.ReactiveAuditingEntityCallback;
+import org.springframework.util.Assert;
+
+/**
+ * {@link ImportBeanDefinitionRegistrar} to enable {@link EnableReactiveMongoAuditing} annotation.
+ *
+ * @author Mark Paluch
+ * @since 3.1
+ */
+class ReactiveMongoAuditingRegistrar extends AuditingBeanDefinitionRegistrarSupport {
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.auditing.config.AuditingBeanDefinitionRegistrarSupport#getAnnotation()
+	 */
+	@Override
+	protected Class<? extends Annotation> getAnnotation() {
+		return EnableReactiveMongoAuditing.class;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.auditing.config.AuditingBeanDefinitionRegistrarSupport#getAuditingHandlerBeanName()
+	 */
+	@Override
+	protected String getAuditingHandlerBeanName() {
+		return "reactiveMongoAuditingHandler";
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.auditing.config.AuditingBeanDefinitionRegistrarSupport#getAuditHandlerBeanDefinitionBuilder(org.springframework.data.auditing.config.AuditingConfiguration)
+	 */
+	@Override
+	protected BeanDefinitionBuilder getAuditHandlerBeanDefinitionBuilder(AuditingConfiguration configuration) {
+
+		Assert.notNull(configuration, "AuditingConfiguration must not be null!");
+
+		BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(ReactiveIsNewAwareAuditingHandler.class);
+
+		BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(PersistentEntitiesFactoryBean.class);
+		definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_CONSTRUCTOR);
+
+		builder.addConstructorArgValue(definition.getBeanDefinition());
+		return configureDefaultAuditHandlerAttributes(configuration, builder);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.auditing.config.AuditingBeanDefinitionRegistrarSupport#registerAuditListener(org.springframework.beans.factory.config.BeanDefinition, org.springframework.beans.factory.support.BeanDefinitionRegistry)
+	 */
+	@Override
+	protected void registerAuditListenerBeanDefinition(BeanDefinition auditingHandlerDefinition,
+			BeanDefinitionRegistry registry) {
+
+		Assert.notNull(auditingHandlerDefinition, "BeanDefinition must not be null!");
+		Assert.notNull(registry, "BeanDefinitionRegistry must not be null!");
+
+		BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(ReactiveAuditingEntityCallback.class);
+
+		builder.addConstructorArgValue(ParsingUtils.getObjectFactoryBeanDefinition(getAuditingHandlerBeanName(), registry));
+		builder.getRawBeanDefinition().setSource(auditingHandlerDefinition.getSource());
+
+		registerInfrastructureBeanWithId(builder.getBeanDefinition(), ReactiveAuditingEntityCallback.class.getName(),
+				registry);
+	}
+
+}

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

@@ -15,8 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AllArgsConstructor;
-
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
@@ -29,7 +27,9 @@ 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;
 import org.springframework.data.mongodb.core.aggregation.TypedAggregation;
 import org.springframework.data.mongodb.core.convert.QueryMapper;
@@ -37,6 +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;
@@ -49,34 +50,50 @@ import org.springframework.util.ObjectUtils;
  * @author Mark Paluch
  * @since 2.1
  */
-@AllArgsConstructor
 class AggregationUtil {
 
 	QueryMapper queryMapper;
 	MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext;
+	Lazy<AggregationOperationContext> untypedMappingContext;
 
-	/**
-	 * 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) {
+	AggregationUtil(QueryMapper queryMapper,
+			MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext) {
 
-		if (context != null) {
-			return context;
+		this.queryMapper = queryMapper;
+		this.mappingContext = mappingContext;
+		this.untypedMappingContext = Lazy
+				.of(() -> new RelaxedTypeBasedAggregationOperationContext(Object.class, mappingContext, queryMapper));
+	}
+
+	AggregationOperationContext createAggregationContext(Aggregation aggregation, @Nullable Class<?> inputType) {
+
+		DomainTypeMapping domainTypeMapping = aggregation.getOptions().getDomainTypeMapping();
+
+		if (domainTypeMapping == DomainTypeMapping.NONE) {
+			return Aggregation.DEFAULT_CONTEXT;
 		}
 
-		if (aggregation instanceof TypedAggregation) {
-			return new TypeBasedAggregationOperationContext(((TypedAggregation) aggregation).getInputType(), mappingContext,
-					queryMapper);
+		if (!(aggregation instanceof TypedAggregation)) {
+
+			if(inputType == null) {
+				return untypedMappingContext.get();
+			}
+
+			if (domainTypeMapping == DomainTypeMapping.STRICT
+					&& !aggregation.getPipeline().containsUnionWith()) {
+				return new TypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper);
+			}
+
+			return new RelaxedTypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper);
 		}
 
-		return Aggregation.DEFAULT_CONTEXT;
+		inputType = ((TypedAggregation<?>) aggregation).getInputType();
+		if (domainTypeMapping == DomainTypeMapping.STRICT
+				&& !aggregation.getPipeline().containsUnionWith()) {
+			return new TypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper);
+		}
+
+		return new RelaxedTypeBasedAggregationOperationContext(inputType, mappingContext, queryMapper);
 	}
 
 	/**
@@ -88,7 +105,7 @@ class AggregationUtil {
 	 */
 	List<Document> createPipeline(Aggregation aggregation, AggregationOperationContext context) {
 
-		if (!ObjectUtils.nullSafeEquals(context, Aggregation.DEFAULT_CONTEXT)) {
+		if (ObjectUtils.nullSafeEquals(context, Aggregation.DEFAULT_CONTEXT)) {
 			return aggregation.toPipeline(context);
 		}
 
@@ -115,53 +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/ChangeStreamEvent.java

@@ -15,8 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.EqualsAndHashCode;
-
 import java.time.Instant;
 import java.util.concurrent.atomic.AtomicReferenceFieldUpdater;
 
@@ -27,6 +25,7 @@ import org.springframework.data.mongodb.core.convert.MongoConverter;
 import org.springframework.data.mongodb.core.messaging.Message;
 import org.springframework.lang.Nullable;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.ObjectUtils;
 
 import com.mongodb.client.model.changestream.ChangeStreamDocument;
 import com.mongodb.client.model.changestream.OperationType;
@@ -39,7 +38,6 @@ import com.mongodb.client.model.changestream.OperationType;
  * @author Mark Paluch
  * @since 2.1
  */
-@EqualsAndHashCode
 public class ChangeStreamEvent<T> {
 
 	@SuppressWarnings("rawtypes") //
@@ -187,8 +185,8 @@ public class ChangeStreamEvent<T> {
 			return CONVERTED_UPDATER.compareAndSet(this, null, result) ? result : CONVERTED_UPDATER.get(this);
 		}
 
-		throw new IllegalArgumentException(String.format("No converter found capable of converting %s to %s",
-				fullDocument.getClass(), targetType));
+		throw new IllegalArgumentException(
+				String.format("No converter found capable of converting %s to %s", fullDocument.getClass(), targetType));
 	}
 
 	/*
@@ -199,4 +197,27 @@ public class ChangeStreamEvent<T> {
 	public String toString() {
 		return "ChangeStreamEvent {" + "raw=" + raw + ", targetType=" + targetType + '}';
 	}
+
+	@Override
+	public boolean equals(Object o) {
+
+		if (this == o)
+			return true;
+		if (o == null || getClass() != o.getClass())
+			return false;
+
+		ChangeStreamEvent<?> that = (ChangeStreamEvent<?>) o;
+
+		if (!ObjectUtils.nullSafeEquals(this.raw, that.raw)) {
+			return false;
+		}
+		return ObjectUtils.nullSafeEquals(this.targetType, that.targetType);
+	}
+
+	@Override
+	public int hashCode() {
+		int result = raw != null ? raw.hashCode() : 0;
+		result = 31 * result + ObjectUtils.nullSafeHashCode(targetType);
+		return result;
+	}
 }

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

@@ -15,8 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.EqualsAndHashCode;
-
 import java.time.Instant;
 import java.util.Arrays;
 import java.util.Optional;
@@ -25,7 +23,6 @@ import org.bson.BsonDocument;
 import org.bson.BsonTimestamp;
 import org.bson.BsonValue;
 import org.bson.Document;
-
 import org.springframework.data.mongodb.core.aggregation.Aggregation;
 import org.springframework.data.mongodb.core.query.Collation;
 import org.springframework.lang.Nullable;
@@ -45,7 +42,6 @@ import com.mongodb.client.model.changestream.FullDocument;
  * @author Mark Paluch
  * @since 2.1
  */
-@EqualsAndHashCode
 public class ChangeStreamOptions {
 
 	private @Nullable Object filter;
@@ -156,6 +152,44 @@ public class ChangeStreamOptions {
 						+ ObjectUtils.nullSafeClassName(timestamp));
 	}
 
+	@Override
+	public boolean equals(Object o) {
+		if (this == o)
+			return true;
+		if (o == null || getClass() != o.getClass())
+			return false;
+
+		ChangeStreamOptions that = (ChangeStreamOptions) o;
+
+		if (!ObjectUtils.nullSafeEquals(this.filter, that.filter)) {
+			return false;
+		}
+		if (!ObjectUtils.nullSafeEquals(this.resumeToken, that.resumeToken)) {
+			return false;
+		}
+		if (!ObjectUtils.nullSafeEquals(this.fullDocumentLookup, that.fullDocumentLookup)) {
+			return false;
+		}
+		if (!ObjectUtils.nullSafeEquals(this.collation, that.collation)) {
+			return false;
+		}
+		if (!ObjectUtils.nullSafeEquals(this.resumeTimestamp, that.resumeTimestamp)) {
+			return false;
+		}
+		return resume == that.resume;
+	}
+
+	@Override
+	public int hashCode() {
+		int result = ObjectUtils.nullSafeHashCode(filter);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(resumeToken);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(fullDocumentLookup);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(collation);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(resumeTimestamp);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(resume);
+		return result;
+	}
+
 	/**
 	 * @author Christoph Strobl
 	 * @since 2.2

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

@@ -15,8 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.RequiredArgsConstructor;
-
 import java.util.Optional;
 
 import org.springframework.data.mongodb.core.query.Collation;
@@ -312,7 +310,6 @@ public class CollectionOptions {
 	 * @author Andreas Zink
 	 * @since 2.1
 	 */
-	@RequiredArgsConstructor
 	public static class ValidationOptions {
 
 		private static final ValidationOptions NONE = new ValidationOptions(null, null, null);
@@ -321,6 +318,13 @@ public class CollectionOptions {
 		private final @Nullable ValidationLevel validationLevel;
 		private final @Nullable ValidationAction validationAction;
 
+		public ValidationOptions(Validator validator, ValidationLevel validationLevel, ValidationAction validationAction) {
+
+			this.validator = validator;
+			this.validationLevel = validationLevel;
+			this.validationAction = validationAction;
+		}
+
 		/**
 		 * Create an empty {@link ValidationOptions}.
 		 *

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

@@ -15,9 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.NonNull;
-import lombok.Value;
-
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -27,8 +24,9 @@ import java.util.stream.Collectors;
 import org.bson.Document;
 import org.bson.conversions.Bson;
 import org.springframework.context.ApplicationEventPublisher;
-import org.springframework.dao.support.PersistenceExceptionTranslator;
+import org.springframework.dao.DataIntegrityViolationException;
 import org.springframework.data.mapping.callback.EntityCallbacks;
+import org.springframework.data.mongodb.BulkOperationException;
 import org.springframework.data.mongodb.core.convert.QueryMapper;
 import org.springframework.data.mongodb.core.convert.UpdateMapper;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
@@ -47,7 +45,9 @@ import org.springframework.data.mongodb.core.query.UpdateDefinition.ArrayFilter;
 import org.springframework.data.util.Pair;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 
+import com.mongodb.MongoBulkWriteException;
 import com.mongodb.WriteConcern;
 import com.mongodb.bulk.BulkWriteResult;
 import com.mongodb.client.MongoCollection;
@@ -64,6 +64,7 @@ import com.mongodb.client.model.*;
  * @author Jens Schauder
  * @author Michail Nikolaev
  * @author Roman Puchkovskiy
+ * @author Jacob Botuck
  * @since 1.9
  */
 class DefaultBulkOperations implements BulkOperations {
@@ -73,7 +74,6 @@ class DefaultBulkOperations implements BulkOperations {
 	private final BulkOperationContext bulkOperationContext;
 	private final List<SourceAwareWriteModelHolder> models = new ArrayList<>();
 
-	private PersistenceExceptionTranslator exceptionTranslator;
 	private @Nullable WriteConcern defaultWriteConcern;
 
 	private BulkWriteOptions bulkOptions;
@@ -97,19 +97,9 @@ class DefaultBulkOperations implements BulkOperations {
 		this.mongoOperations = mongoOperations;
 		this.collectionName = collectionName;
 		this.bulkOperationContext = bulkOperationContext;
-		this.exceptionTranslator = new MongoExceptionTranslator();
 		this.bulkOptions = getBulkWriteOptions(bulkOperationContext.getBulkMode());
 	}
 
-	/**
-	 * Configures the {@link PersistenceExceptionTranslator} to be used. Defaults to {@link MongoExceptionTranslator}.
-	 *
-	 * @param exceptionTranslator can be {@literal null}.
-	 */
-	public void setExceptionTranslator(@Nullable PersistenceExceptionTranslator exceptionTranslator) {
-		this.exceptionTranslator = exceptionTranslator == null ? new MongoExceptionTranslator() : exceptionTranslator;
-	}
-
 	/**
 	 * Configures the default {@link WriteConcern} to be used. Defaults to {@literal null}.
 	 *
@@ -316,11 +306,26 @@ class DefaultBulkOperations implements BulkOperations {
 			collection = collection.withWriteConcern(defaultWriteConcern);
 		}
 
-		return collection.bulkWrite( //
-				models.stream() //
-						.map(this::extractAndMapWriteModel) //
-						.collect(Collectors.toList()), //
-				bulkOptions);
+		try {
+
+			return collection.bulkWrite( //
+					models.stream() //
+							.map(this::extractAndMapWriteModel) //
+							.collect(Collectors.toList()), //
+					bulkOptions);
+		} catch (RuntimeException ex) {
+
+			if (ex instanceof MongoBulkWriteException) {
+
+				MongoBulkWriteException mongoBulkWriteException = (MongoBulkWriteException) ex;
+				if (mongoBulkWriteException.getWriteConcernError() != null) {
+					throw new DataIntegrityViolationException(ex.getMessage(), ex);
+				}
+				throw new BulkOperationException(ex.getMessage(), mongoBulkWriteException);
+			}
+
+			throw ex;
+		}
 	}
 
 	private WriteModel<Document> extractAndMapWriteModel(SourceAwareWriteModelHolder it) {
@@ -547,15 +552,93 @@ class DefaultBulkOperations implements BulkOperations {
 	 * @author Christoph Strobl
 	 * @since 2.0
 	 */
-	@Value
-	static class BulkOperationContext {
+	static final class BulkOperationContext {
 
-		@NonNull BulkMode bulkMode;
-		@NonNull Optional<? extends MongoPersistentEntity<?>> entity;
-		@NonNull QueryMapper queryMapper;
-		@NonNull UpdateMapper updateMapper;
-		ApplicationEventPublisher eventPublisher;
-		EntityCallbacks entityCallbacks;
+		private final BulkMode bulkMode;
+		private final Optional<? extends MongoPersistentEntity<?>> entity;
+		private final QueryMapper queryMapper;
+		private final UpdateMapper updateMapper;
+		private final ApplicationEventPublisher eventPublisher;
+		private final EntityCallbacks entityCallbacks;
+
+		BulkOperationContext(BulkOperations.BulkMode bulkMode, Optional<? extends MongoPersistentEntity<?>> entity,
+				QueryMapper queryMapper, UpdateMapper updateMapper, ApplicationEventPublisher eventPublisher,
+				EntityCallbacks entityCallbacks) {
+
+			this.bulkMode = bulkMode;
+			this.entity = entity;
+			this.queryMapper = queryMapper;
+			this.updateMapper = updateMapper;
+			this.eventPublisher = eventPublisher;
+			this.entityCallbacks = entityCallbacks;
+		}
+
+		public BulkMode getBulkMode() {
+			return this.bulkMode;
+		}
+
+		public Optional<? extends MongoPersistentEntity<?>> getEntity() {
+			return this.entity;
+		}
+
+		public QueryMapper getQueryMapper() {
+			return this.queryMapper;
+		}
+
+		public UpdateMapper getUpdateMapper() {
+			return this.updateMapper;
+		}
+
+		public ApplicationEventPublisher getEventPublisher() {
+			return this.eventPublisher;
+		}
+
+		public EntityCallbacks getEntityCallbacks() {
+			return this.entityCallbacks;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if (this == o)
+				return true;
+			if (o == null || getClass() != o.getClass())
+				return false;
+
+			BulkOperationContext that = (BulkOperationContext) o;
+
+			if (bulkMode != that.bulkMode)
+				return false;
+			if (!ObjectUtils.nullSafeEquals(this.entity, that.entity)) {
+				return false;
+			}
+			if (!ObjectUtils.nullSafeEquals(this.queryMapper, that.queryMapper)) {
+				return false;
+			}
+			if (!ObjectUtils.nullSafeEquals(this.updateMapper, that.updateMapper)) {
+				return false;
+			}
+			if (!ObjectUtils.nullSafeEquals(this.eventPublisher, that.eventPublisher)) {
+				return false;
+			}
+			return ObjectUtils.nullSafeEquals(this.entityCallbacks, that.entityCallbacks);
+		}
+
+		@Override
+		public int hashCode() {
+			int result = bulkMode != null ? bulkMode.hashCode() : 0;
+			result = 31 * result + ObjectUtils.nullSafeHashCode(entity);
+			result = 31 * result + ObjectUtils.nullSafeHashCode(queryMapper);
+			result = 31 * result + ObjectUtils.nullSafeHashCode(updateMapper);
+			result = 31 * result + ObjectUtils.nullSafeHashCode(eventPublisher);
+			result = 31 * result + ObjectUtils.nullSafeHashCode(entityCallbacks);
+			return result;
+		}
+
+		public String toString() {
+			return "DefaultBulkOperations.BulkOperationContext(bulkMode=" + this.getBulkMode() + ", entity="
+					+ this.getEntity() + ", queryMapper=" + this.getQueryMapper() + ", updateMapper=" + this.getUpdateMapper()
+					+ ", eventPublisher=" + this.getEventPublisher() + ", entityCallbacks=" + this.getEntityCallbacks() + ")";
+		}
 	}
 
 	/**
@@ -564,10 +647,50 @@ class DefaultBulkOperations implements BulkOperations {
 	 * @since 2.2
 	 * @author Christoph Strobl
 	 */
-	@Value
-	private static class SourceAwareWriteModelHolder {
+	private static final class SourceAwareWriteModelHolder {
 
-		Object source;
-		WriteModel<Document> model;
+		private final Object source;
+		private final WriteModel<Document> model;
+
+		SourceAwareWriteModelHolder(Object source, WriteModel<Document> model) {
+
+			this.source = source;
+			this.model = model;
+		}
+
+		public Object getSource() {
+			return this.source;
+		}
+
+		public WriteModel<Document> getModel() {
+			return this.model;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if (this == o)
+				return true;
+			if (o == null || getClass() != o.getClass())
+				return false;
+
+			SourceAwareWriteModelHolder that = (SourceAwareWriteModelHolder) o;
+
+			if (!ObjectUtils.nullSafeEquals(this.source, that.source)) {
+				return false;
+			}
+			return ObjectUtils.nullSafeEquals(this.model, that.model);
+		}
+
+		@Override
+		public int hashCode() {
+			int result = ObjectUtils.nullSafeHashCode(model);
+			result = 31 * result + ObjectUtils.nullSafeHashCode(source);
+			return result;
+		}
+
+		public String toString() {
+			return "DefaultBulkOperations.SourceAwareWriteModelHolder(source=" + this.getSource() + ", model="
+					+ this.getModel() + ")";
+		}
 	}
 }

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/EntityOperations.java

@@ -15,11 +15,8 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-
 import java.util.Collection;
+import java.util.Iterator;
 import java.util.Map;
 import java.util.Optional;
 
@@ -44,6 +41,7 @@ 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;
 
 /**
  * Common operations performed on an entity in the context of it's mapping metadata.
@@ -55,12 +53,15 @@ import org.springframework.util.MultiValueMap;
  * @see MongoTemplate
  * @see ReactiveMongoTemplate
  */
-@RequiredArgsConstructor
 class EntityOperations {
 
 	private static final String ID_FIELD = "_id";
 
-	private final @NonNull MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> context;
+	private final MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> context;
+
+	EntityOperations(MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> context) {
+		this.context = context;
+	}
 
 	/**
 	 * Creates a new {@link Entity} for the given bean.
@@ -69,7 +70,7 @@ class EntityOperations {
 	 * @return new instance of {@link Entity}.
 	 */
 	@SuppressWarnings({ "unchecked", "rawtypes" })
-	public <T> Entity<T> forEntity(T entity) {
+	<T> Entity<T> forEntity(T entity) {
 
 		Assert.notNull(entity, "Bean must not be null!");
 
@@ -92,7 +93,7 @@ class EntityOperations {
 	 * @return new instance of {@link AdaptibleEntity}.
 	 */
 	@SuppressWarnings({ "unchecked", "rawtypes" })
-	public <T> AdaptibleEntity<T> forEntity(T entity, ConversionService conversionService) {
+	<T> AdaptibleEntity<T> forEntity(T entity, ConversionService conversionService) {
 
 		Assert.notNull(entity, "Bean must not be null!");
 		Assert.notNull(conversionService, "ConversionService must not be null!");
@@ -108,6 +109,20 @@ 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}.
@@ -346,11 +361,14 @@ class EntityOperations {
 		Number getVersion();
 	}
 
-	@RequiredArgsConstructor
 	private static class UnmappedEntity<T extends Map<String, Object>> implements AdaptibleEntity<T> {
 
 		private final T map;
 
+		protected UnmappedEntity(T map) {
+			this.map = map;
+		}
+
 		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.EntityOperations.PersistableSource#getIdPropertyName()
@@ -460,7 +478,7 @@ class EntityOperations {
 
 	private static class SimpleMappedEntity<T extends Map<String, Object>> extends UnmappedEntity<T> {
 
-		SimpleMappedEntity(T map) {
+		protected SimpleMappedEntity(T map) {
 			super(map);
 		}
 
@@ -483,12 +501,19 @@ class EntityOperations {
 		}
 	}
 
-	@RequiredArgsConstructor(access = AccessLevel.PROTECTED)
 	private static class MappedEntity<T> implements Entity<T> {
 
-		private final @NonNull MongoPersistentEntity<?> entity;
-		private final @NonNull IdentifierAccessor idAccessor;
-		private final @NonNull PersistentPropertyAccessor<T> propertyAccessor;
+		private final MongoPersistentEntity<?> entity;
+		private final IdentifierAccessor idAccessor;
+		private final PersistentPropertyAccessor<T> propertyAccessor;
+
+		protected MappedEntity(MongoPersistentEntity<?> entity, IdentifierAccessor idAccessor,
+				PersistentPropertyAccessor<T> propertyAccessor) {
+
+			this.entity = entity;
+			this.idAccessor = idAccessor;
+			this.propertyAccessor = propertyAccessor;
+		}
 
 		private static <T> MappedEntity<T> of(T bean,
 				MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> context) {
@@ -759,11 +784,12 @@ class EntityOperations {
 	 * {@link TypedOperations} for generic entities that are not represented with {@link PersistentEntity} (e.g. custom
 	 * conversions).
 	 */
-	@RequiredArgsConstructor
 	enum UntypedOperations implements TypedOperations<Object> {
 
 		INSTANCE;
 
+		UntypedOperations() {}
+
 		@SuppressWarnings({ "unchecked", "rawtypes" })
 		public static <T> TypedOperations<T> instance() {
 			return (TypedOperations) INSTANCE;
@@ -798,10 +824,13 @@ class EntityOperations {
 	 *
 	 * @param <T>
 	 */
-	@RequiredArgsConstructor
 	static class TypedEntityOperations<T> implements TypedOperations<T> {
 
-		private final @NonNull MongoPersistentEntity<T> entity;
+		private final MongoPersistentEntity<T> entity;
+
+		protected TypedEntityOperations(MongoPersistentEntity<T> entity) {
+			this.entity = entity;
+		}
 
 		/*
 		 * (non-Javadoc)

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

@@ -15,16 +15,10 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
-
 import org.springframework.data.mongodb.core.aggregation.Aggregation;
 import org.springframework.data.mongodb.core.aggregation.AggregationResults;
 import org.springframework.data.mongodb.core.aggregation.TypedAggregation;
 import org.springframework.data.util.CloseableIterator;
-import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
 
@@ -35,10 +29,13 @@ import org.springframework.util.StringUtils;
  * @author Mark Paluch
  * @since 2.0
  */
-@RequiredArgsConstructor
 class ExecutableAggregationOperationSupport implements ExecutableAggregationOperation {
 
-	private final @NonNull MongoTemplate template;
+	private final MongoTemplate template;
+
+	ExecutableAggregationOperationSupport(MongoTemplate template) {
+		this.template = template;
+	}
 
 	/*
 	 * (non-Javadoc)
@@ -56,15 +53,21 @@ class ExecutableAggregationOperationSupport implements ExecutableAggregationOper
 	 * @author Christoph Strobl
 	 * @since 2.0
 	 */
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ExecutableAggregationSupport<T>
 			implements AggregationWithAggregation<T>, ExecutableAggregation<T>, TerminatingAggregation<T> {
 
-		@NonNull MongoTemplate template;
-		@NonNull Class<T> domainType;
-		@Nullable Aggregation aggregation;
-		@Nullable String collection;
+		private final MongoTemplate template;
+		private final Class<T> domainType;
+		private final Aggregation aggregation;
+		private final String collection;
+
+		public ExecutableAggregationSupport(MongoTemplate template, Class<T> domainType, Aggregation aggregation,
+				String collection) {
+			this.template = template;
+			this.domainType = domainType;
+			this.aggregation = aggregation;
+			this.collection = collection;
+		}
 
 		/*
 		 * (non-Javadoc)

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.
+		 * <p />
+		 * 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/ExecutableFindOperationSupport.java

@@ -15,12 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import com.mongodb.ReadPreference;
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
-
 import java.util.List;
 import java.util.Optional;
 import java.util.stream.Stream;
@@ -37,6 +31,7 @@ import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 
+import com.mongodb.ReadPreference;
 import com.mongodb.client.FindIterable;
 
 /**
@@ -46,12 +41,15 @@ import com.mongodb.client.FindIterable;
  * @author Mark Paluch
  * @since 2.0
  */
-@RequiredArgsConstructor
 class ExecutableFindOperationSupport implements ExecutableFindOperation {
 
 	private static final Query ALL_QUERY = new Query();
 
-	private final @NonNull MongoTemplate template;
+	private final MongoTemplate template;
+
+	ExecutableFindOperationSupport(MongoTemplate template) {
+		this.template = template;
+	}
 
 	/*
 	 * (non-Javadoc)
@@ -70,16 +68,23 @@ class ExecutableFindOperationSupport implements ExecutableFindOperation {
 	 * @author Christoph Strobl
 	 * @since 2.0
 	 */
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ExecutableFindSupport<T>
 			implements ExecutableFind<T>, FindWithCollection<T>, FindWithProjection<T>, FindWithQuery<T> {
 
-		@NonNull MongoTemplate template;
-		@NonNull Class<?> domainType;
-		Class<T> returnType;
-		@Nullable String collection;
-		Query query;
+		private final MongoTemplate template;
+		private final Class<?> domainType;
+		private final Class<T> returnType;
+		@Nullable private final String collection;
+		private final Query query;
+
+		ExecutableFindSupport(MongoTemplate template, Class<?> domainType, Class<T> returnType,
+				String collection, Query query) {
+			this.template = template;
+			this.domainType = domainType;
+			this.returnType = returnType;
+			this.collection = collection;
+			this.query = query;
+		}
 
 		/*
 		 * (non-Javadoc)

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

@@ -15,11 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
-
 import java.util.ArrayList;
 import java.util.Collection;
 
@@ -37,10 +32,13 @@ import com.mongodb.bulk.BulkWriteResult;
  * @author Mark Paluch
  * @since 2.0
  */
-@RequiredArgsConstructor
 class ExecutableInsertOperationSupport implements ExecutableInsertOperation {
 
-	private final @NonNull MongoTemplate template;
+	private final MongoTemplate template;
+
+	ExecutableInsertOperationSupport(MongoTemplate template) {
+		this.template = template;
+	}
 
 	/*
 	 * (non-Javadoc)
@@ -58,14 +56,20 @@ class ExecutableInsertOperationSupport implements ExecutableInsertOperation {
 	 * @author Christoph Strobl
 	 * @since 2.0
 	 */
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ExecutableInsertSupport<T> implements ExecutableInsert<T> {
 
-		@NonNull MongoTemplate template;
-		@NonNull Class<T> domainType;
-		@Nullable String collection;
-		@Nullable BulkMode bulkMode;
+		private final MongoTemplate template;
+		private final Class<T> domainType;
+		@Nullable private final String collection;
+		@Nullable private final BulkMode bulkMode;
+
+		ExecutableInsertSupport(MongoTemplate template, Class<T> domainType, String collection, BulkMode bulkMode) {
+
+			this.template = template;
+			this.domainType = domainType;
+			this.collection = collection;
+			this.bulkMode = bulkMode;
+		}
 
 		/*
 		 * (non-Javadoc)

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

@@ -15,9 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-
 import java.util.List;
 
 import org.springframework.data.mongodb.core.mapreduce.MapReduceOptions;
@@ -32,12 +29,17 @@ import org.springframework.util.StringUtils;
  * @author Christoph Strobl
  * @since 2.1
  */
-@RequiredArgsConstructor
 class ExecutableMapReduceOperationSupport implements ExecutableMapReduceOperation {
 
 	private static final Query ALL_QUERY = new Query();
 
-	private final @NonNull MongoTemplate template;
+	private final MongoTemplate template;
+
+	ExecutableMapReduceOperationSupport(MongoTemplate template) {
+
+		Assert.notNull(template, "Template must not be null!");
+		this.template = template;
+	}
 
 	/*
 	 * (non-Javascript)

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

@@ -15,11 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
-
 import java.util.List;
 
 import org.springframework.data.mongodb.core.query.Query;
@@ -36,12 +31,15 @@ import com.mongodb.client.result.DeleteResult;
  * @author Mark Paluch
  * @since 2.0
  */
-@RequiredArgsConstructor
 class ExecutableRemoveOperationSupport implements ExecutableRemoveOperation {
 
 	private static final Query ALL_QUERY = new Query();
 
-	private final @NonNull MongoTemplate tempate;
+	private final MongoTemplate tempate;
+
+	public ExecutableRemoveOperationSupport(MongoTemplate tempate) {
+		this.tempate = tempate;
+	}
 
 	/*
 	 * (non-Javadoc)
@@ -59,14 +57,19 @@ class ExecutableRemoveOperationSupport implements ExecutableRemoveOperation {
 	 * @author Christoph Strobl
 	 * @since 2.0
 	 */
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ExecutableRemoveSupport<T> implements ExecutableRemove<T>, RemoveWithCollection<T> {
 
-		@NonNull MongoTemplate template;
-		@NonNull Class<T> domainType;
-		Query query;
-		@Nullable String collection;
+		private final MongoTemplate template;
+		private final Class<T> domainType;
+		private final Query query;
+		@Nullable private final String collection;
+
+		public ExecutableRemoveSupport(MongoTemplate template, Class<T> domainType, Query query, String collection) {
+			this.template = template;
+			this.domainType = domainType;
+			this.query = query;
+			this.collection = collection;
+		}
 
 		/*
 		 * (non-Javadoc)

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

@@ -15,11 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
-
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.core.query.UpdateDefinition;
 import org.springframework.lang.Nullable;
@@ -35,12 +30,15 @@ import com.mongodb.client.result.UpdateResult;
  * @author Mark Paluch
  * @since 2.0
  */
-@RequiredArgsConstructor
 class ExecutableUpdateOperationSupport implements ExecutableUpdateOperation {
 
 	private static final Query ALL_QUERY = new Query();
 
-	private final @NonNull MongoTemplate template;
+	private final MongoTemplate template;
+
+	ExecutableUpdateOperationSupport(MongoTemplate template) {
+		this.template = template;
+	}
 
 	/*
 	 * (non-Javadoc)
@@ -58,21 +56,34 @@ class ExecutableUpdateOperationSupport implements ExecutableUpdateOperation {
 	 * @author Christoph Strobl
 	 * @since 2.0
 	 */
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ExecutableUpdateSupport<T>
 			implements ExecutableUpdate<T>, UpdateWithCollection<T>, UpdateWithQuery<T>, TerminatingUpdate<T>,
 			FindAndReplaceWithOptions<T>, TerminatingFindAndReplace<T>, FindAndReplaceWithProjection<T> {
 
-		@NonNull MongoTemplate template;
-		@NonNull Class domainType;
-		Query query;
-		@Nullable UpdateDefinition update;
-		@Nullable String collection;
-		@Nullable FindAndModifyOptions findAndModifyOptions;
-		@Nullable FindAndReplaceOptions findAndReplaceOptions;
-		@Nullable Object replacement;
-		@NonNull Class<T> targetType;
+		private final MongoTemplate template;
+		private final Class domainType;
+		private final Query query;
+		@Nullable private final UpdateDefinition update;
+		@Nullable private final String collection;
+		@Nullable private final FindAndModifyOptions findAndModifyOptions;
+		@Nullable private final FindAndReplaceOptions findAndReplaceOptions;
+		@Nullable private final Object replacement;
+		private final Class<T> targetType;
+
+		ExecutableUpdateSupport(MongoTemplate template, Class domainType, Query query, UpdateDefinition update,
+				String collection, FindAndModifyOptions findAndModifyOptions, FindAndReplaceOptions findAndReplaceOptions,
+				Object replacement, Class<T> targetType) {
+
+			this.template = template;
+			this.domainType = domainType;
+			this.query = query;
+			this.update = update;
+			this.collection = collection;
+			this.findAndModifyOptions = findAndModifyOptions;
+			this.findAndReplaceOptions = findAndReplaceOptions;
+			this.replacement = replacement;
+			this.targetType = targetType;
+		}
 
 		/*
 		 * (non-Javadoc)

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

@@ -15,9 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.Getter;
-import lombok.RequiredArgsConstructor;
-
 import java.util.Collection;
 import java.util.List;
 
@@ -27,8 +24,6 @@ import org.springframework.data.mongodb.core.query.Update;
 import org.springframework.data.mongodb.core.query.UpdateDefinition;
 import org.springframework.data.util.StreamUtils;
 
-import com.mongodb.client.model.Filters;
-
 /**
  * A MongoDB document in its mapped state. I.e. after a source document has been mapped using mapping information of the
  * entity the source document was supposed to represent.
@@ -36,13 +31,20 @@ import com.mongodb.client.model.Filters;
  * @author Oliver Gierke
  * @since 2.1
  */
-@RequiredArgsConstructor(staticName = "of")
 public class MappedDocument {
 
 	private static final String ID_FIELD = "_id";
 	private static final Document ID_ONLY_PROJECTION = new Document(ID_FIELD, 1);
 
-	private final @Getter Document document;
+	private final Document document;
+
+	private MappedDocument(Document document) {
+		this.document = document;
+	}
+
+	public static MappedDocument of(Document document) {
+		return new MappedDocument(document);
+	}
 
 	public static Document getIdOnlyProjection() {
 		return ID_ONLY_PROJECTION;
@@ -91,6 +93,10 @@ public class MappedDocument {
 		return new MappedUpdate(Update.fromDocument(document, ID_FIELD));
 	}
 
+	public Document getDocument() {
+		return this.document;
+	}
+
 	/**
 	 * An {@link UpdateDefinition} that indicates that the {@link #getUpdateObject() update object} has already been
 	 * mapped to the specific domain type.

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

@@ -15,8 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.Value;
-
 import org.springframework.aop.framework.ProxyFactory;
 import org.springframework.dao.DataAccessException;
 import org.springframework.dao.support.PersistenceExceptionTranslator;
@@ -24,6 +22,7 @@ import org.springframework.data.mongodb.MongoDatabaseFactory;
 import org.springframework.data.mongodb.SessionAwareMethodInterceptor;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 
 import com.mongodb.ClientSessionOptions;
 import com.mongodb.WriteConcern;
@@ -171,11 +170,15 @@ public abstract class MongoDatabaseFactorySupport<C> implements MongoDatabaseFac
 	 * @author Christoph Strobl
 	 * @since 2.1
 	 */
-	@Value
-	static class ClientSessionBoundMongoDbFactory implements MongoDatabaseFactory {
+	static final class ClientSessionBoundMongoDbFactory implements MongoDatabaseFactory {
 
-		ClientSession session;
-		MongoDatabaseFactory delegate;
+		private final ClientSession session;
+		private final MongoDatabaseFactory delegate;
+
+		public ClientSessionBoundMongoDbFactory(ClientSession session, MongoDatabaseFactory delegate) {
+			this.session = session;
+			this.delegate = delegate;
+		}
 
 		/*
 		 * (non-Javadoc)
@@ -256,5 +259,40 @@ public abstract class MongoDatabaseFactorySupport<C> implements MongoDatabaseFac
 
 			return targetType.cast(factory.getProxy(target.getClass().getClassLoader()));
 		}
+
+		public ClientSession getSession() {
+			return this.session;
+		}
+
+		public MongoDatabaseFactory getDelegate() {
+			return this.delegate;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if (this == o)
+				return true;
+			if (o == null || getClass() != o.getClass())
+				return false;
+
+			ClientSessionBoundMongoDbFactory that = (ClientSessionBoundMongoDbFactory) o;
+
+			if (!ObjectUtils.nullSafeEquals(this.session, that.session)) {
+				return false;
+			}
+			return ObjectUtils.nullSafeEquals(this.delegate, that.delegate);
+		}
+
+		@Override
+		public int hashCode() {
+			int result = ObjectUtils.nullSafeHashCode(this.session);
+			result = 31 * result + ObjectUtils.nullSafeHashCode(this.delegate);
+			return result;
+		}
+
+		public String toString() {
+			return "MongoDatabaseFactorySupport.ClientSessionBoundMongoDbFactory(session=" + this.getSession() + ", delegate="
+					+ this.getDelegate() + ")";
+		}
 	}
 }

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

@@ -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.
+	 * <p />
+	 * 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.
+	 * <p />
+	 * 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.
@@ -1184,6 +1196,35 @@ public interface MongoOperations extends FluentMongoOperations {
 	 */
 	long count(Query query, String collectionName);
 
+	/**
+	 * Estimate the number of documents, in the collection {@link #getCollectionName(Class) identified by the given type},
+	 * based on collection statistics.
+	 * <p />
+	 * 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.
+	 * @since 3.1
+	 */
+	default long estimatedCount(Class<?> entityClass) {
+
+		Assert.notNull(entityClass, "Entity class must not be null!");
+		return estimatedCount(getCollectionName(entityClass));
+	}
+
+	/**
+	 * Estimate the number of documents in the given collection based on collection statistics.
+	 * <p />
+	 * 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.
+	 * @since 3.1
+	 */
+	long estimatedCount(String collectionName);
+
 	/**
 	 * Returns the number of documents for the given {@link Query} by querying the given collection using the given entity
 	 * class to map the given {@link Query}. <br />
@@ -1191,6 +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.
+	 * <p />
+	 * 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}.
@@ -1211,11 +1258,13 @@ public interface MongoOperations extends FluentMongoOperations {
 	 * <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/>
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.
+	 * <p/>
+	 * 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);
 
@@ -1226,10 +1275,13 @@ public interface MongoOperations extends FluentMongoOperations {
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
 	 * <p/>
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.
+	 * <p/>
+	 * 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);
 
@@ -1272,9 +1324,12 @@ public interface MongoOperations extends FluentMongoOperations {
 	 * 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 />
+	 * 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);
 
@@ -1290,10 +1345,13 @@ public interface MongoOperations extends FluentMongoOperations {
 	 * 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.
+	 * <p />
+	 * 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/MongoTemplate.java

@@ -17,11 +17,6 @@ package org.springframework.data.mongodb.core;
 
 import static org.springframework.data.mongodb.core.query.SerializationUtils.*;
 
-import lombok.AccessLevel;
-import lombok.AllArgsConstructor;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-
 import java.io.IOException;
 import java.math.BigDecimal;
 import java.math.RoundingMode;
@@ -33,7 +28,6 @@ import org.bson.Document;
 import org.bson.conversions.Bson;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
 import org.springframework.beans.BeansException;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
@@ -60,6 +54,7 @@ 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;
@@ -160,22 +155,14 @@ import com.mongodb.client.result.UpdateResult;
  * @author Cimon Lucas
  * @author Michael J. Simons
  * @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;
@@ -718,12 +705,17 @@ 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);
 	}
 
 	/*
@@ -731,7 +723,7 @@ 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);
 	}
 
 	/*
@@ -763,7 +755,6 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 				new BulkOperationContext(mode, Optional.ofNullable(getPersistentEntity(entityType)), queryMapper, updateMapper,
 						eventPublisher, entityCallbacks));
 
-		operations.setExceptionTranslator(exceptionTranslator);
 		operations.setDefaultWriteConcern(writeConcern);
 
 		return operations;
@@ -1140,6 +1131,19 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 				collection -> collection.countDocuments(CountQuery.of(filter).toQueryDocument(), options));
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.core.MongoOperations#estimatedCount(java.lang.String)
+	 */
+	@Override
+	public long estimatedCount(String collectionName) {
+		return doEstimatedCount(collectionName, new EstimatedDocumentCountOptions());
+	}
+
+	protected long doEstimatedCount(String collectionName, EstimatedDocumentCountOptions options) {
+		return execute(collectionName, collection -> collection.estimatedDocumentCount(options));
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.MongoOperations#insert(java.lang.Object)
@@ -1168,11 +1172,28 @@ 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.");
 		}
 	}
 
@@ -1355,6 +1376,7 @@ 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());
 
@@ -1969,9 +1991,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 
 		Assert.notNull(aggregation, "Aggregation pipeline must not be null!");
 
-		AggregationOperationContext context = new TypeBasedAggregationOperationContext(aggregation.getInputType(),
-				mappingContext, queryMapper);
-		return aggregate(aggregation, inputCollectionName, outputType, context);
+		return aggregate(aggregation, inputCollectionName, outputType, null);
 	}
 
 	/* (non-Javadoc)
@@ -1981,7 +2001,7 @@ 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)
@@ -2088,9 +2108,13 @@ 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")
@@ -2141,6 +2165,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 			}
 
 			options.getComment().ifPresent(aggregateIterable::comment);
+			options.getHint().ifPresent(aggregateIterable::hint);
 
 			if (options.hasExecutionTimeLimit()) {
 				aggregateIterable = aggregateIterable.maxTime(options.getMaxTime().toMillis(), TimeUnit.MILLISECONDS);
@@ -2177,11 +2202,10 @@ 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);
@@ -2199,6 +2223,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 			}
 
 			options.getComment().ifPresent(cursor::comment);
+			options.getHint().ifPresent(cursor::hint);
 
 			Class<?> domainType = aggregation instanceof TypedAggregation ? ((TypedAggregation) aggregation).getInputType()
 					: null;
@@ -2961,12 +2986,17 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @author Christoph Strobl
 	 * @since 2.0
 	 */
-	@RequiredArgsConstructor
 	private class ExistsCallback implements CollectionCallback<Boolean> {
 
 		private final Document mappedQuery;
 		private final com.mongodb.client.model.Collation collation;
 
+		ExistsCallback(Document mappedQuery, com.mongodb.client.model.Collation collation) {
+
+			this.mappedQuery = mappedQuery;
+			this.collation = collation;
+		}
+
 		@Override
 		public Boolean doInCollection(MongoCollection<Document> collection) throws MongoException, DataAccessException {
 
@@ -2988,7 +3018,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		private final Document sort;
 		private final Optional<Collation> collation;
 
-		public FindAndRemoveCallback(Document query, Document fields, Document sort, @Nullable Collation collation) {
+		FindAndRemoveCallback(Document query, Document fields, Document sort, @Nullable Collation collation) {
 
 			this.query = query;
 			this.fields = fields;
@@ -3014,8 +3044,9 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		private final List<Document> arrayFilters;
 		private final FindAndModifyOptions options;
 
-		public FindAndModifyCallback(Document query, Document fields, Document sort, Object update,
-				List<Document> arrayFilters, FindAndModifyOptions options) {
+		FindAndModifyCallback(Document query, Document fields, Document sort, Object update, List<Document> arrayFilters,
+				FindAndModifyOptions options) {
+
 			this.query = query;
 			this.fields = fields;
 			this.sort = sort;
@@ -3124,13 +3155,19 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @author Christoph Strobl
 	 * @author Roman Puchkovskiy
 	 */
-	@RequiredArgsConstructor
 	private class ReadDocumentCallback<T> implements DocumentCallback<T> {
 
-		private final @NonNull EntityReader<? super T, Bson> reader;
-		private final @NonNull Class<T> type;
+		private final EntityReader<? super T, Bson> reader;
+		private final Class<T> type;
 		private final String collectionName;
 
+		ReadDocumentCallback(EntityReader<? super T, Bson> reader, Class<T> type, String collectionName) {
+
+			this.reader = reader;
+			this.type = type;
+			this.collectionName = collectionName;
+		}
+
 		@Nullable
 		public T doWith(@Nullable Document document) {
 
@@ -3158,13 +3195,21 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @param <T>
 	 * @since 2.0
 	 */
-	@RequiredArgsConstructor
 	private class ProjectingReadCallback<S, T> implements DocumentCallback<T> {
 
-		private final @NonNull EntityReader<Object, Bson> reader;
-		private final @NonNull Class<S> entityType;
-		private final @NonNull Class<T> targetType;
-		private final @NonNull String collectionName;
+		private final EntityReader<Object, Bson> reader;
+		private final Class<S> entityType;
+		private final Class<T> targetType;
+		private final String collectionName;
+
+		ProjectingReadCallback(EntityReader<Object, Bson> reader, Class<S> entityType, Class<T> targetType,
+				String collectionName) {
+
+			this.reader = reader;
+			this.entityType = entityType;
+			this.targetType = targetType;
+			this.collectionName = collectionName;
+		}
 
 		/*
 		 * (non-Javadoc)
@@ -3200,7 +3245,7 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		private final Query query;
 		private final @Nullable Class<?> type;
 
-		public QueryCursorPreparer(Query query, @Nullable Class<?> type) {
+		QueryCursorPreparer(Query query, @Nullable Class<?> type) {
 
 			this.query = query;
 			this.type = type;
@@ -3261,6 +3306,10 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 						cursorToUse = cursorToUse.batchSize(meta.getCursorBatchSize());
 					}
 
+					if (meta.getAllowDiskUse() != null) {
+						cursorToUse = cursorToUse.allowDiskUse(meta.getAllowDiskUse());
+					}
+
 					for (Meta.CursorOption option : meta.getFlags()) {
 
 						switch (option) {
@@ -3344,7 +3393,6 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 	 * @author Thomas Darimont
 	 * @since 1.7
 	 */
-	@AllArgsConstructor(access = AccessLevel.PACKAGE)
 	static class CloseableIterableCursorAdapter<T> implements CloseableIterator<T> {
 
 		private volatile @Nullable MongoCursor<Document> cursor;
@@ -3358,14 +3406,22 @@ public class MongoTemplate implements MongoOperations, ApplicationContextAware,
 		 * @param exceptionTranslator
 		 * @param objectReadCallback
 		 */
-		public CloseableIterableCursorAdapter(MongoIterable<Document> cursor,
-				PersistenceExceptionTranslator exceptionTranslator, DocumentCallback<T> objectReadCallback) {
+		CloseableIterableCursorAdapter(MongoIterable<Document> cursor, PersistenceExceptionTranslator exceptionTranslator,
+				DocumentCallback<T> objectReadCallback) {
 
 			this.cursor = cursor.iterator();
 			this.exceptionTranslator = exceptionTranslator;
 			this.objectReadCallback = objectReadCallback;
 		}
 
+		CloseableIterableCursorAdapter(MongoCursor<Document> cursor, PersistenceExceptionTranslator exceptionTranslator,
+				DocumentCallback<T> objectReadCallback) {
+
+			this.cursor = cursor;
+			this.exceptionTranslator = exceptionTranslator;
+			this.objectReadCallback = objectReadCallback;
+		}
+
 		@Override
 		public boolean hasNext() {
 
@@ -3419,7 +3475,20 @@ 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;
 	}
 

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

@@ -15,9 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.RequiredArgsConstructor;
-
 import org.bson.Document;
 import org.springframework.data.mapping.SimplePropertyHandler;
 import org.springframework.data.mapping.context.MappingContext;
@@ -33,11 +30,14 @@ import org.springframework.util.ClassUtils;
  * @author Christoph Strobl
  * @since 2.1
  */
-@RequiredArgsConstructor(access = AccessLevel.PACKAGE)
 class PropertyOperations {
 
 	private final MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext;
 
+	PropertyOperations(MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext) {
+		this.mappingContext = mappingContext;
+	}
+
 	/**
 	 * For cases where {@code fields} is {@link Document#isEmpty() empty} include only fields that are required for
 	 * creating the projection (target) type if the {@code targetType} is a {@literal DTO projection} or a

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);
 		}
 
@@ -708,10 +756,10 @@ class QueryOperations {
 		 */
 		List<Document> getUpdatePipeline(@Nullable Class<?> domainType) {
 
-			AggregationOperationContext context = domainType != null
-					? new RelaxedTypeBasedAggregationOperationContext(domainType, mappingContext, queryMapper)
-					: Aggregation.DEFAULT_CONTEXT;
+			Class<?> type = domainType != null ? domainType : Object.class;
 
+			AggregationOperationContext context = new RelaxedTypeBasedAggregationOperationContext(type, mappingContext,
+					queryMapper);
 			return aggregationUtil.createPipeline((AggregationUpdate) update, context);
 		}
 
@@ -761,4 +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/ReactiveAggregationOperationSupport.java

@@ -15,10 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
 import reactor.core.publisher.Flux;
 
 import org.springframework.data.mongodb.core.aggregation.Aggregation;
@@ -62,15 +58,22 @@ class ReactiveAggregationOperationSupport implements ReactiveAggregationOperatio
 		return new ReactiveAggregationSupport<>(template, domainType, null, null);
 	}
 
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ReactiveAggregationSupport<T>
 			implements AggregationOperationWithAggregation<T>, ReactiveAggregation<T>, TerminatingAggregationOperation<T> {
 
-		@NonNull ReactiveMongoTemplate template;
-		@NonNull Class<T> domainType;
-		Aggregation aggregation;
-		String collection;
+		private final ReactiveMongoTemplate template;
+		private final Class<T> domainType;
+		private final Aggregation aggregation;
+		private final String collection;
+
+		ReactiveAggregationSupport(ReactiveMongoTemplate template, Class<T> domainType, Aggregation aggregation,
+				String collection) {
+
+			this.template = template;
+			this.domainType = domainType;
+			this.aggregation = aggregation;
+			this.collection = collection;
+		}
 
 		/*
 		 * (non-Javadoc)

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

@@ -106,6 +106,12 @@ public interface ReactiveFindOperation {
 
 		/**
 		 * Get the number of matching elements.
+		 * <p />
+		 * 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/ReactiveFindOperationSupport.java

@@ -15,15 +15,10 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
 import org.bson.Document;
-
 import org.springframework.dao.IncorrectResultSizeDataAccessException;
 import org.springframework.data.mongodb.core.query.NearQuery;
 import org.springframework.data.mongodb.core.query.Query;
@@ -39,12 +34,15 @@ import org.springframework.util.StringUtils;
  * @author Christoph Strobl
  * @since 2.0
  */
-@RequiredArgsConstructor
 class ReactiveFindOperationSupport implements ReactiveFindOperation {
 
 	private static final Query ALL_QUERY = new Query();
 
-	private final @NonNull ReactiveMongoTemplate template;
+	private final ReactiveMongoTemplate template;
+
+	ReactiveFindOperationSupport(ReactiveMongoTemplate template) {
+		this.template = template;
+	}
 
 	/*
 	 * (non-Javadoc)
@@ -64,16 +62,24 @@ class ReactiveFindOperationSupport implements ReactiveFindOperation {
 	 * @author Christoph Strobl
 	 * @since 2.0
 	 */
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ReactiveFindSupport<T>
 			implements ReactiveFind<T>, FindWithCollection<T>, FindWithProjection<T>, FindWithQuery<T> {
 
-		@NonNull ReactiveMongoTemplate template;
-		@NonNull Class<?> domainType;
-		Class<T> returnType;
-		String collection;
-		Query query;
+		private final ReactiveMongoTemplate template;
+		private final Class<?> domainType;
+		private final Class<T> returnType;
+		private final String collection;
+		private final Query query;
+
+		ReactiveFindSupport(ReactiveMongoTemplate template, Class<?> domainType, Class<T> returnType,
+				String collection, Query query) {
+
+			this.template = template;
+			this.domainType = domainType;
+			this.returnType = returnType;
+			this.collection = collection;
+			this.query = query;
+		}
 
 		/*
 		 * (non-Javadoc)

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

@@ -15,10 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -34,10 +30,13 @@ import org.springframework.util.StringUtils;
  * @author Christoph Strobl
  * @since 2.0
  */
-@RequiredArgsConstructor
 class ReactiveInsertOperationSupport implements ReactiveInsertOperation {
 
-	private final @NonNull ReactiveMongoTemplate template;
+	private final ReactiveMongoTemplate template;
+
+	ReactiveInsertOperationSupport(ReactiveMongoTemplate template) {
+		this.template = template;
+	}
 
 	/*
 	 * (non-Javadoc)
@@ -51,13 +50,18 @@ class ReactiveInsertOperationSupport implements ReactiveInsertOperation {
 		return new ReactiveInsertSupport<>(template, domainType, null);
 	}
 
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ReactiveInsertSupport<T> implements ReactiveInsert<T> {
 
-		@NonNull ReactiveMongoTemplate template;
-		@NonNull Class<T> domainType;
-		String collection;
+		private final ReactiveMongoTemplate template;
+		private final Class<T> domainType;
+		private final String collection;
+
+		ReactiveInsertSupport(ReactiveMongoTemplate template, Class<T> domainType, String collection) {
+
+			this.template = template;
+			this.domainType = domainType;
+			this.collection = collection;
+		}
 
 		/*
 		 * (non-Javadoc)

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

@@ -15,8 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
 import reactor.core.publisher.Flux;
 
 import org.springframework.data.mongodb.core.mapreduce.MapReduceOptions;
@@ -31,12 +29,15 @@ import org.springframework.util.StringUtils;
  * @author Christoph Strobl
  * @since 2.1
  */
-@RequiredArgsConstructor
 class ReactiveMapReduceOperationSupport implements ReactiveMapReduceOperation {
 
 	private static final Query ALL_QUERY = new Query();
 
-	private final @NonNull ReactiveMongoTemplate template;
+	private final ReactiveMongoTemplate template;
+
+	ReactiveMapReduceOperationSupport(ReactiveMongoTemplate template) {
+		this.template = template;
+	}
 
 	/*
 	 * (non-Javascript)

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

@@ -15,11 +15,15 @@
  */
 package org.springframework.data.mongodb.core;
 
-import org.reactivestreams.Publisher;
-import org.springframework.util.Assert;
 import reactor.core.publisher.Mono;
 import reactor.util.context.Context;
 
+import java.util.function.Function;
+
+import org.reactivestreams.Publisher;
+
+import org.springframework.util.Assert;
+
 import com.mongodb.reactivestreams.client.ClientSession;
 
 /**
@@ -29,7 +33,7 @@ import com.mongodb.reactivestreams.client.ClientSession;
  * @author Christoph Strobl
  * @author Mark Paluch
  * @since 2.1
- * @see Mono#subscriberContext()
+ * @see Mono#deferContextual(Function)
  * @see Context
  */
 public class ReactiveMongoContext {
@@ -46,8 +50,14 @@ public class ReactiveMongoContext {
 	 */
 	public static Mono<ClientSession> getSession() {
 
-		return Mono.subscriberContext().filter(ctx -> ctx.hasKey(SESSION_KEY))
-				.flatMap(ctx -> ctx.<Mono<ClientSession>> get(SESSION_KEY));
+		return Mono.deferContextual(ctx -> {
+
+			if (ctx.hasKey(SESSION_KEY)) {
+				return ctx.<Mono<ClientSession>> get(SESSION_KEY);
+			}
+
+			return Mono.empty();
+		});
 	}
 
 	/**

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

@@ -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.
+	 * <p />
+	 * 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.
+	 * <p />
+	 * 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.
+	 * <p />
+	 * 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}.
@@ -980,6 +998,35 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 */
 	Mono<Long> count(Query query, @Nullable Class<?> entityClass, String collectionName);
 
+	/**
+	 * Estimate the number of documents, in the collection {@link #getCollectionName(Class) identified by the given type},
+	 * based on collection statistics.
+	 * <p />
+	 * 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.
+	 * @since 3.1
+	 */
+	default Mono<Long> estimatedCount(Class<?> entityClass) {
+
+		Assert.notNull(entityClass, "Entity class must not be null!");
+		return estimatedCount(getCollectionName(entityClass));
+	}
+
+	/**
+	 * Estimate the number of documents in the given collection based on collection statistics.
+	 * <p />
+	 * 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.
+	 * @since 3.1
+	 */
+	Mono<Long> estimatedCount(String collectionName);
+
 	/**
 	 * Insert the object into the collection for the entity type of the object to save.
 	 * <p/>
@@ -991,11 +1038,13 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * <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/>
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.
+	 * <p />
+	 * 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);
 
@@ -1006,10 +1055,13 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * configured otherwise, an instance of {@link MappingMongoConverter} will be used.
 	 * <p/>
 	 * Insert is used to initially store the object into the database. To update an existing object use the save method.
+	 * <p />
+	 * 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);
 
@@ -1051,7 +1103,6 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * <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/>
 	 * 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}.
@@ -1098,9 +1149,12 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * 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 />
+	 * 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);
 
@@ -1120,6 +1174,7 @@ public interface ReactiveMongoOperations extends ReactiveFluentMongoOperations {
 	 * @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);
 

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

@@ -17,9 +17,6 @@ package org.springframework.data.mongodb.core;
 
 import static org.springframework.data.mongodb.core.query.SerializationUtils.*;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.util.function.Tuple2;
@@ -39,7 +36,6 @@ import org.reactivestreams.Publisher;
 import org.reactivestreams.Subscriber;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
 import org.springframework.beans.BeansException;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.ApplicationContextAware;
@@ -64,6 +60,7 @@ 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;
@@ -73,6 +70,7 @@ 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;
@@ -120,16 +118,7 @@ import com.mongodb.CursorType;
 import com.mongodb.MongoException;
 import com.mongodb.ReadPreference;
 import com.mongodb.WriteConcern;
-import com.mongodb.client.model.CountOptions;
-import com.mongodb.client.model.CreateCollectionOptions;
-import com.mongodb.client.model.DeleteOptions;
-import com.mongodb.client.model.FindOneAndDeleteOptions;
-import com.mongodb.client.model.FindOneAndReplaceOptions;
-import com.mongodb.client.model.FindOneAndUpdateOptions;
-import com.mongodb.client.model.ReplaceOptions;
-import com.mongodb.client.model.ReturnDocument;
-import com.mongodb.client.model.UpdateOptions;
-import com.mongodb.client.model.ValidationOptions;
+import com.mongodb.client.model.*;
 import com.mongodb.client.model.changestream.FullDocument;
 import com.mongodb.client.result.DeleteResult;
 import com.mongodb.client.result.InsertOneResult;
@@ -158,6 +147,7 @@ import com.mongodb.reactivestreams.client.MongoDatabase;
  * @author Christoph Strobl
  * @author Roman Puchkovskiy
  * @author Mathieu Ouellet
+ * @author Yadhukrishna S Pai
  * @since 2.0
  */
 public class ReactiveMongoTemplate implements ReactiveMongoOperations, ApplicationContextAware {
@@ -166,18 +156,6 @@ 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;
@@ -584,7 +562,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 				ReactiveMongoTemplate.this);
 
 		return Flux.from(action.doInSession(operations)) //
-				.subscriberContext(ctx -> ReactiveMongoContext.setSession(ctx, Mono.just(session)));
+				.contextWrite(ctx -> ReactiveMongoContext.setSession(ctx, Mono.just(session)));
 	}
 
 	/*
@@ -956,9 +934,7 @@ 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);
 	}
 
 	/*
@@ -976,9 +952,7 @@ 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);
 	}
 
 	/*
@@ -987,40 +961,29 @@ 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,
+				collection -> aggregateAndMap(collection, ctx.getAggregationPipeline(), ctx.isOutOrMerge(), options,
 						readCallback,
-						aggregation instanceof TypedAggregation ? ((TypedAggregation<?>) aggregation).getInputType() : null));
+						ctx.getInputType()));
 	}
 
 	private <O> Flux<O> aggregateAndMap(MongoCollection<Document> collection, List<Document> pipeline,
@@ -1035,6 +998,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 		}
 
 		options.getComment().ifPresent(cursor::comment);
+		options.getHint().ifPresent(cursor::hint);
 
 		Optionals.firstNonEmpty(options::getCollation, () -> operations.forType(inputType).getCollation()) //
 				.map(Collation::toMongoCollation) //
@@ -1258,6 +1222,15 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 		});
 	}
 
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.core.ReactiveMongoOperations#estimatedCount(java.lang.String)
+	 */
+	@Override
+	public Mono<Long> estimatedCount(String collectionName) {
+		return doEstimatedCount(collectionName, new EstimatedDocumentCountOptions());
+	}
+
 	/**
 	 * Run the actual count operation against the collection with given name.
 	 *
@@ -1272,6 +1245,11 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 				collection -> collection.countDocuments(CountQuery.of(filter).toQueryDocument(), options));
 	}
 
+	protected Mono<Long> doEstimatedCount(String collectionName, EstimatedDocumentCountOptions options) {
+
+		return createMono(collectionName, collection -> collection.estimatedDocumentCount(options));
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.ReactiveMongoOperations#insert(reactor.core.publisher.Mono)
@@ -2108,7 +2086,7 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 			AggregationOperationContext context = agg instanceof TypedAggregation
 					? new TypeBasedAggregationOperationContext(((TypedAggregation<?>) agg).getInputType(),
 							getConverter().getMappingContext(), queryMapper)
-					: Aggregation.DEFAULT_CONTEXT;
+					: new RelaxedTypeBasedAggregationOperationContext(Object.class, mappingContext, queryMapper);
 
 			return agg.toPipeline(new PrefixingDelegatingAggregationOperationContext(context, "fullDocument",
 					Arrays.asList("operationType", "fullDocument", "documentKey", "updateDescription", "ns")));
@@ -2418,8 +2396,8 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 * @param query the query document that specifies the criteria used to find a record.
 	 * @param fields the document that specifies the fields to be returned.
 	 * @param entityClass the parameterized type of the returned list.
-	 * @param preparer allows for customization of the {@link com.mongodb.client.FindIterable} used when iterating over the result set, (apply
-	 *          limits, skips and so on).
+	 * @param preparer allows for customization of the {@link com.mongodb.client.FindIterable} used when iterating over
+	 *          the result set, (apply limits, skips and so on).
 	 * @return the {@link List} of converted objects.
 	 */
 	protected <T> Flux<T> doFind(String collectionName, Document query, Document fields, Class<T> entityClass,
@@ -2677,13 +2655,27 @@ 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.");
 		}
 	}
@@ -2725,6 +2717,14 @@ 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) {
 
@@ -2893,7 +2893,6 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 *
 	 * @author Mark Paluch
 	 */
-	@RequiredArgsConstructor
 	private static class FindCallback implements ReactiveCollectionQueryCallback<Document> {
 
 		private final @Nullable Document query;
@@ -2903,6 +2902,12 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 			this(query, null);
 		}
 
+		FindCallback(Document query, Document fields) {
+
+			this.query = query;
+			this.fields = fields;
+		}
+
 		@Override
 		public FindPublisher<Document> doInCollection(MongoCollection<Document> collection) {
 
@@ -2956,7 +2961,6 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	/**
 	 * @author Mark Paluch
 	 */
-	@RequiredArgsConstructor
 	private static class FindAndModifyCallback implements ReactiveCollectionCallback<Document> {
 
 		private final Document query;
@@ -2966,6 +2970,17 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 		private final List<Document> arrayFilters;
 		private final FindAndModifyOptions options;
 
+		FindAndModifyCallback(Document query, Document fields, Document sort, Object update, List<Document> arrayFilters,
+				FindAndModifyOptions options) {
+
+			this.query = query;
+			this.fields = fields;
+			this.sort = sort;
+			this.update = update;
+			this.arrayFilters = arrayFilters;
+			this.options = options;
+		}
+
 		@Override
 		public Publisher<Document> doInCollection(MongoCollection<Document> collection)
 				throws MongoException, DataAccessException {
@@ -3021,7 +3036,6 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 * @author Christoph Strobl
 	 * @since 2.1
 	 */
-	@RequiredArgsConstructor(access = AccessLevel.PACKAGE)
 	private static class FindAndReplaceCallback implements ReactiveCollectionCallback<Document> {
 
 		private final Document query;
@@ -3031,6 +3045,17 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 		private final @Nullable com.mongodb.client.model.Collation collation;
 		private final FindAndReplaceOptions options;
 
+		FindAndReplaceCallback(Document query, Document fields, Document sort, Document update,
+				com.mongodb.client.model.Collation collation, FindAndReplaceOptions options) {
+
+			this.query = query;
+			this.fields = fields;
+			this.sort = sort;
+			this.update = update;
+			this.collation = collation;
+			this.options = options;
+		}
+
 		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.ReactiveCollectionCallback#doInCollection(com.mongodb.reactivestreams.client.MongoCollection)
@@ -3147,13 +3172,20 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 	 * @author Roman Puchkovskiy
 	 * @since 2.0
 	 */
-	@RequiredArgsConstructor
 	private class ProjectingReadCallback<S, T> implements DocumentCallback<T> {
 
-		private final @NonNull EntityReader<Object, Bson> reader;
-		private final @NonNull Class<S> entityType;
-		private final @NonNull Class<T> targetType;
-		private final @NonNull String collectionName;
+		private final EntityReader<Object, Bson> reader;
+		private final Class<S> entityType;
+		private final Class<T> targetType;
+		private final String collectionName;
+
+		ProjectingReadCallback(EntityReader<Object, Bson> reader, Class<S> entityType, Class<T> targetType,
+				String collectionName) {
+			this.reader = reader;
+			this.entityType = entityType;
+			this.targetType = targetType;
+			this.collectionName = collectionName;
+		}
 
 		@SuppressWarnings("unchecked")
 		public Mono<T> doWith(Document document) {
@@ -3292,6 +3324,10 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 					if (meta.getCursorBatchSize() != null) {
 						findPublisherToUse = findPublisherToUse.batchSize(meta.getCursorBatchSize());
 					}
+
+					if (meta.getAllowDiskUse() != null) {
+						findPublisherToUse = findPublisherToUse.allowDiskUse(meta.getAllowDiskUse());
+					}
 				}
 
 			} catch (RuntimeException e) {
@@ -3374,11 +3410,14 @@ public class ReactiveMongoTemplate implements ReactiveMongoOperations, Applicati
 		}
 	}
 
-	@RequiredArgsConstructor
 	class IndexCreatorEventListener implements ApplicationListener<MappingContextEvent<?, ?>> {
 
 		final Consumer<Throwable> subscriptionExceptionHandler;
 
+		public IndexCreatorEventListener(Consumer<Throwable> subscriptionExceptionHandler) {
+			this.subscriptionExceptionHandler = subscriptionExceptionHandler;
+		}
+
 		@Override
 		public void onApplicationEvent(MappingContextEvent<?, ?> event) {
 

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

@@ -15,10 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 
@@ -35,12 +31,15 @@ import com.mongodb.client.result.DeleteResult;
  * @author Christoph Strobl
  * @since 2.0
  */
-@RequiredArgsConstructor
 class ReactiveRemoveOperationSupport implements ReactiveRemoveOperation {
 
 	private static final Query ALL_QUERY = new Query();
 
-	private final @NonNull ReactiveMongoTemplate tempate;
+	private final ReactiveMongoTemplate tempate;
+
+	ReactiveRemoveOperationSupport(ReactiveMongoTemplate tempate) {
+		this.tempate = tempate;
+	}
 
 	/*
 	 * (non-Javadoc)
@@ -54,14 +53,20 @@ class ReactiveRemoveOperationSupport implements ReactiveRemoveOperation {
 		return new ReactiveRemoveSupport<>(tempate, domainType, ALL_QUERY, null);
 	}
 
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ReactiveRemoveSupport<T> implements ReactiveRemove<T>, RemoveWithCollection<T> {
 
-		@NonNull ReactiveMongoTemplate template;
-		@NonNull Class<T> domainType;
-		Query query;
-		String collection;
+		private final ReactiveMongoTemplate template;
+		private final Class<T> domainType;
+		private final Query query;
+		private final String collection;
+
+		ReactiveRemoveSupport(ReactiveMongoTemplate template, Class<T> domainType, Query query, String collection) {
+
+			this.template = template;
+			this.domainType = domainType;
+			this.query = query;
+			this.collection = collection;
+		}
 
 		/*
 		 * (non-Javadoc)

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

@@ -15,13 +15,10 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-import lombok.experimental.FieldDefaults;
 import reactor.core.publisher.Mono;
 
 import org.springframework.data.mongodb.core.query.Query;
+import org.springframework.data.mongodb.core.query.UpdateDefinition;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
@@ -35,12 +32,15 @@ import com.mongodb.client.result.UpdateResult;
  * @author Christoph Strobl
  * @since 2.0
  */
-@RequiredArgsConstructor
 class ReactiveUpdateOperationSupport implements ReactiveUpdateOperation {
 
 	private static final Query ALL_QUERY = new Query();
 
-	private final @NonNull ReactiveMongoTemplate template;
+	private final ReactiveMongoTemplate template;
+
+	ReactiveUpdateOperationSupport(ReactiveMongoTemplate template) {
+		this.template = template;
+	}
 
 	/*
 	 * (non-Javadoc)
@@ -54,21 +54,34 @@ class ReactiveUpdateOperationSupport implements ReactiveUpdateOperation {
 		return new ReactiveUpdateSupport<>(template, domainType, ALL_QUERY, null, null, null, null, null, domainType);
 	}
 
-	@RequiredArgsConstructor
-	@FieldDefaults(level = AccessLevel.PRIVATE, makeFinal = true)
 	static class ReactiveUpdateSupport<T>
 			implements ReactiveUpdate<T>, UpdateWithCollection<T>, UpdateWithQuery<T>, TerminatingUpdate<T>,
 			FindAndReplaceWithOptions<T>, FindAndReplaceWithProjection<T>, TerminatingFindAndReplace<T> {
 
-		@NonNull ReactiveMongoTemplate template;
-		@NonNull Class<?> domainType;
-		Query query;
-		org.springframework.data.mongodb.core.query.UpdateDefinition update;
-		@Nullable String collection;
-		@Nullable FindAndModifyOptions findAndModifyOptions;
-		@Nullable FindAndReplaceOptions findAndReplaceOptions;
-		@Nullable Object replacement;
-		@NonNull Class<T> targetType;
+		private final ReactiveMongoTemplate template;
+		private final Class<?> domainType;
+		private final Query query;
+		private final org.springframework.data.mongodb.core.query.UpdateDefinition update;
+		@Nullable private final String collection;
+		@Nullable private final FindAndModifyOptions findAndModifyOptions;
+		@Nullable private final FindAndReplaceOptions findAndReplaceOptions;
+		@Nullable private final Object replacement;
+		private final Class<T> targetType;
+
+		ReactiveUpdateSupport(ReactiveMongoTemplate template, Class<?> domainType, Query query, UpdateDefinition update,
+				String collection, FindAndModifyOptions findAndModifyOptions, FindAndReplaceOptions findAndReplaceOptions,
+				Object replacement, Class<T> targetType) {
+
+			this.template = template;
+			this.domainType = domainType;
+			this.query = query;
+			this.update = update;
+			this.collection = collection;
+			this.findAndModifyOptions = findAndModifyOptions;
+			this.findAndReplaceOptions = findAndReplaceOptions;
+			this.replacement = replacement;
+			this.targetType = targetType;
+		}
 
 		/*
 		 * (non-Javadoc)
@@ -123,7 +136,9 @@ class ReactiveUpdateOperationSupport implements ReactiveUpdateOperation {
 
 			String collectionName = getCollectionName();
 
-			return template.findAndModify(query, update, findAndModifyOptions != null ? findAndModifyOptions : FindAndModifyOptions.none(), targetType, collectionName);
+			return template.findAndModify(query, update,
+					findAndModifyOptions != null ? findAndModifyOptions : FindAndModifyOptions.none(), targetType,
+					collectionName);
 		}
 
 		/*

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

@@ -15,7 +15,6 @@
  */
 package org.springframework.data.mongodb.core;
 
-import lombok.Value;
 import reactor.core.publisher.Mono;
 
 import org.bson.codecs.configuration.CodecRegistry;
@@ -27,6 +26,7 @@ import org.springframework.data.mongodb.ReactiveMongoDatabaseFactory;
 import org.springframework.data.mongodb.SessionAwareMethodInterceptor;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 
 import com.mongodb.ClientSessionOptions;
 import com.mongodb.ConnectionString;
@@ -175,11 +175,16 @@ public class SimpleReactiveMongoDatabaseFactory implements DisposableBean, React
 	 * @author Christoph Strobl
 	 * @since 2.1
 	 */
-	@Value
-	static class ClientSessionBoundMongoDbFactory implements ReactiveMongoDatabaseFactory {
+	static final class ClientSessionBoundMongoDbFactory implements ReactiveMongoDatabaseFactory {
 
-		ClientSession session;
-		ReactiveMongoDatabaseFactory delegate;
+		private final ClientSession session;
+		private final ReactiveMongoDatabaseFactory delegate;
+
+		ClientSessionBoundMongoDbFactory(ClientSession session, ReactiveMongoDatabaseFactory delegate) {
+
+			this.session = session;
+			this.delegate = delegate;
+		}
 
 		/*
 		 * (non-Javadoc)
@@ -268,5 +273,40 @@ public class SimpleReactiveMongoDatabaseFactory implements DisposableBean, React
 
 			return targetType.cast(factory.getProxy(target.getClass().getClassLoader()));
 		}
+
+		public ClientSession getSession() {
+			return this.session;
+		}
+
+		public ReactiveMongoDatabaseFactory getDelegate() {
+			return this.delegate;
+		}
+
+		@Override
+		public boolean equals(Object o) {
+			if (this == o)
+				return true;
+			if (o == null || getClass() != o.getClass())
+				return false;
+
+			ClientSessionBoundMongoDbFactory that = (ClientSessionBoundMongoDbFactory) o;
+
+			if (!ObjectUtils.nullSafeEquals(this.session, that.session)) {
+				return false;
+			}
+			return ObjectUtils.nullSafeEquals(this.delegate, that.delegate);
+		}
+
+		@Override
+		public int hashCode() {
+			int result = ObjectUtils.nullSafeHashCode(this.session);
+			result = 31 * result + ObjectUtils.nullSafeHashCode(this.delegate);
+			return result;
+		}
+
+		public String toString() {
+			return "SimpleReactiveMongoDatabaseFactory.ClientSessionBoundMongoDbFactory(session=" + this.getSession()
+					+ ", delegate=" + this.getDelegate() + ")";
+		}
 	}
 }

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

@@ -29,8 +29,11 @@ import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
 
 /**
+ * Support class for {@link AggregationExpression} implementations.
+ *
  * @author Christoph Strobl
  * @author Matt Morrissette
+ * @author Mark Paluch
  * @since 1.10
  */
 abstract class AbstractAggregationExpression implements AggregationExpression {
@@ -49,7 +52,6 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 		return toDocument(this.value, context);
 	}
 
-	@SuppressWarnings("unchecked")
 	public Document toDocument(Object value, AggregationOperationContext context) {
 		return new Document(getMongoMethod(), unpack(value, context));
 	}
@@ -101,17 +103,19 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 		return value;
 	}
 
+	@SuppressWarnings("unchecked")
 	protected List<Object> append(Object value, Expand expandList) {
 
 		if (this.value instanceof List) {
 
-			List<Object> clone = new ArrayList<Object>((List) this.value);
+			List<Object> clone = new ArrayList<>((List<Object>) this.value);
 
 			if (value instanceof Collection && Expand.EXPAND_VALUES.equals(expandList)) {
 				clone.addAll((Collection<?>) value);
 			} else {
 				clone.add(value);
 			}
+
 			return clone;
 		}
 
@@ -129,25 +133,72 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 		return append(value, Expand.EXPAND_VALUES);
 	}
 
-	@SuppressWarnings("unchecked")
-	protected java.util.Map<String, Object> append(String key, Object value) {
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	protected Map<String, Object> append(String key, Object value) {
 
 		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map!");
 
-		java.util.Map<String, Object> clone = new LinkedHashMap<>((java.util.Map) this.value);
+		Map<String, Object> clone = new LinkedHashMap<>((java.util.Map) this.value);
 		clone.put(key, value);
 		return clone;
 
 	}
 
+	@SuppressWarnings({ "unchecked", "rawtypes" })
+	protected Map<String, Object> remove(String key) {
+
+		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map!");
+
+		Map<String, Object> clone = new LinkedHashMap<>((java.util.Map) this.value);
+		clone.remove(key);
+		return clone;
+	}
+
+	/**
+	 * Append the given key at the position in the underlying {@link LinkedHashMap}.
+	 *
+	 * @param index
+	 * @param key
+	 * @param value
+	 * @return
+	 * @since 3.1
+	 */
+	@SuppressWarnings({ "unchecked" })
+	protected Map<String, Object> appendAt(int index, String key, Object value) {
+
+		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map!");
+
+		Map<String, Object> clone = new LinkedHashMap<>();
+
+		int i = 0;
+		for (Map.Entry<String, Object> entry : ((Map<String, Object>) this.value).entrySet()) {
+
+			if (i == index) {
+				clone.put(key, value);
+			}
+			if (!entry.getKey().equals(key)) {
+				clone.put(entry.getKey(), entry.getValue());
+			}
+			i++;
+		}
+		if (i <= index) {
+			clone.put(key, value);
+		}
+		return clone;
+
+	}
+
+	@SuppressWarnings({ "rawtypes" })
 	protected List<Object> values() {
 
 		if (value instanceof List) {
 			return new ArrayList<Object>((List) value);
 		}
+
 		if (value instanceof java.util.Map) {
 			return new ArrayList<Object>(((java.util.Map) value).values());
 		}
+
 		return new ArrayList<>(Collections.singletonList(value));
 	}
 
@@ -177,7 +228,7 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 
 		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map!");
 
-		return (T) ((java.util.Map<String, Object>) this.value).get(key);
+		return (T) ((Map<String, Object>) this.value).get(key);
 	}
 
 	/**
@@ -187,11 +238,11 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 	 * @return
 	 */
 	@SuppressWarnings("unchecked")
-	protected java.util.Map<String, Object> argumentMap() {
+	protected Map<String, Object> argumentMap() {
 
 		Assert.isInstanceOf(Map.class, this.value, "Value must be a type of Map!");
 
-		return Collections.unmodifiableMap((java.util.Map) value);
+		return Collections.unmodifiableMap((java.util.Map<String, Object>) value);
 	}
 
 	/**
@@ -208,7 +259,7 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 			return false;
 		}
 
-		return ((java.util.Map<String, Object>) this.value).containsKey(key);
+		return ((Map<String, Object>) this.value).containsKey(key);
 	}
 
 	protected abstract String getMongoMethod();

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

@@ -32,6 +32,7 @@ import org.springframework.util.Assert;
  * @author Oliver Gierke
  * @author Christoph Strobl
  * @author Mark Paluch
+ * @author Yadhukrishna S Pai
  * @see Aggregation#withOptions(AggregationOptions)
  * @see TypedAggregation#withOptions(AggregationOptions)
  * @since 1.6
@@ -45,14 +46,17 @@ public class AggregationOptions {
 	private static final String COLLATION = "collation";
 	private static final String COMMENT = "comment";
 	private static final String MAX_TIME = "maxTimeMS";
+	private static final String HINT = "hint";
 
 	private final boolean allowDiskUse;
 	private final boolean explain;
 	private final Optional<Document> cursor;
 	private final Optional<Collation> collation;
 	private final Optional<String> comment;
+	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}.
@@ -71,13 +75,13 @@ public class AggregationOptions {
 	 * @param allowDiskUse whether to off-load intensive sort-operations to disk.
 	 * @param explain whether to get the execution plan for the aggregation instead of the actual results.
 	 * @param cursor can be {@literal null}, used to pass additional options (such as {@code batchSize}) to the
-	 * aggregation.
+	 *          aggregation.
 	 * @param collation collation for string comparison. Can be {@literal null}.
 	 * @since 2.0
 	 */
 	public AggregationOptions(boolean allowDiskUse, boolean explain, @Nullable Document cursor,
 			@Nullable Collation collation) {
-		this(allowDiskUse, explain, cursor, collation, null);
+		this(allowDiskUse, explain, cursor, collation, null, null);
 	}
 
 	/**
@@ -86,19 +90,37 @@ public class AggregationOptions {
 	 * @param allowDiskUse whether to off-load intensive sort-operations to disk.
 	 * @param explain whether to get the execution plan for the aggregation instead of the actual results.
 	 * @param cursor can be {@literal null}, used to pass additional options (such as {@code batchSize}) to the
-	 * aggregation.
+	 *          aggregation.
 	 * @param collation collation for string comparison. Can be {@literal null}.
 	 * @param comment execution comment. Can be {@literal null}.
 	 * @since 2.2
 	 */
 	public AggregationOptions(boolean allowDiskUse, boolean explain, @Nullable Document cursor,
 			@Nullable Collation collation, @Nullable String comment) {
+		this(allowDiskUse, explain, cursor, collation, comment, null);
+	}
+
+	/**
+	 * Creates a new {@link AggregationOptions}.
+	 *
+	 * @param allowDiskUse whether to off-load intensive sort-operations to disk.
+	 * @param explain whether to get the execution plan for the aggregation instead of the actual results.
+	 * @param cursor can be {@literal null}, used to pass additional options (such as {@code batchSize}) to the
+	 *          aggregation.
+	 * @param collation collation for string comparison. Can be {@literal null}.
+	 * @param comment execution comment. Can be {@literal null}.
+	 * @param hint can be {@literal null}, used to provide an index that would be forcibly used by query optimizer.
+	 * @since 3.1
+	 */
+	private AggregationOptions(boolean allowDiskUse, boolean explain, @Nullable Document cursor,
+			@Nullable Collation collation, @Nullable String comment, @Nullable Document hint) {
 
 		this.allowDiskUse = allowDiskUse;
 		this.explain = explain;
 		this.cursor = Optional.ofNullable(cursor);
 		this.collation = Optional.ofNullable(collation);
 		this.comment = Optional.ofNullable(comment);
+		this.hint = Optional.ofNullable(hint);
 	}
 
 	/**
@@ -130,8 +152,9 @@ public class AggregationOptions {
 		Collation collation = document.containsKey(COLLATION) ? Collation.from(document.get(COLLATION, Document.class))
 				: null;
 		String comment = document.getString(COMMENT);
+		Document hint = document.get(HINT, Document.class);
 
-		AggregationOptions options = new AggregationOptions(allowDiskUse, explain, cursor, collation, comment);
+		AggregationOptions options = new AggregationOptions(allowDiskUse, explain, cursor, collation, comment, hint);
 		if (document.containsKey(MAX_TIME)) {
 			options.maxTime = Duration.ofMillis(document.getLong(MAX_TIME));
 		}
@@ -212,6 +235,16 @@ public class AggregationOptions {
 		return comment;
 	}
 
+	/**
+	 * Get the hint used to to fulfill the aggregation.
+	 *
+	 * @return never {@literal null}.
+	 * @since 3.1
+	 */
+	public Optional<Document> getHint() {
+		return hint;
+	}
+
 	/**
 	 * @return the time limit for processing. {@link Duration#ZERO} is used for the default unbounded behavior.
 	 * @since 3.0
@@ -229,6 +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.
@@ -248,6 +289,10 @@ public class AggregationOptions {
 			result.put(EXPLAIN, explain);
 		}
 
+		if (result.containsKey(HINT)) {
+			hint.ifPresent(val -> result.append(HINT, val));
+		}
+
 		if (!result.containsKey(CURSOR)) {
 			cursor.ifPresent(val -> result.put(CURSOR, val));
 		}
@@ -277,6 +322,7 @@ public class AggregationOptions {
 		cursor.ifPresent(val -> document.put(CURSOR, val));
 		collation.ifPresent(val -> document.append(COLLATION, val.toDocument()));
 		comment.ifPresent(val -> document.append(COMMENT, val));
+		hint.ifPresent(val -> document.append(HINT, val));
 
 		if (hasExecutionTimeLimit()) {
 			document.append(MAX_TIME, maxTime.toMillis());
@@ -318,8 +364,10 @@ public class AggregationOptions {
 		private @Nullable Document cursor;
 		private @Nullable Collation collation;
 		private @Nullable String comment;
+		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.
@@ -396,11 +444,24 @@ public class AggregationOptions {
 			return this;
 		}
 
+		/**
+		 * Define a hint that is used by query optimizer to to fulfill the aggregation.
+		 *
+		 * @param hint can be {@literal null}.
+		 * @return this.
+		 * @since 3.1
+		 */
+		public Builder hint(@Nullable Document hint) {
+
+			this.hint = hint;
+			return this;
+		}
+
 		/**
 		 * Set the time limit for processing.
 		 *
 		 * @param maxTime {@link Duration#ZERO} is used for the default unbounded behavior. {@link Duration#isNegative()
-		 * Negative} values will be ignored.
+		 *          Negative} values will be ignored.
 		 * @return this.
 		 * @since 3.0
 		 */
@@ -424,6 +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.
 		 *
@@ -431,13 +530,16 @@ public class AggregationOptions {
 		 */
 		public AggregationOptions build() {
 
-			AggregationOptions options = new AggregationOptions(allowDiskUse, explain, cursor, collation, comment);
+			AggregationOptions options = new AggregationOptions(allowDiskUse, explain, cursor, collation, comment, hint);
 			if (maxTime != null) {
 				options.maxTime = maxTime;
 			}
 			if (resultOptions != null) {
 				options.resultOptions = resultOptions;
 			}
+			if (domainTypeMapping != null) {
+				options.domainTypeMapping = domainTypeMapping;
+			}
 
 			return options;
 		}
@@ -457,4 +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/AggregationPipeline.java

@@ -18,6 +18,7 @@ package org.springframework.data.mongodb.core.aggregation;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.function.Predicate;
 
 import org.bson.Document;
 import org.springframework.util.Assert;
@@ -26,6 +27,7 @@ import org.springframework.util.Assert;
  * The {@link AggregationPipeline} holds the collection of {@link AggregationOperation aggregation stages}.
  *
  * @author Christoph Strobl
+ * @author Mark Paluch
  * @since 3.0.2
  */
 public class AggregationPipeline {
@@ -45,6 +47,8 @@ public class AggregationPipeline {
 	 * @param aggregationOperations must not be {@literal null}.
 	 */
 	public AggregationPipeline(List<AggregationOperation> aggregationOperations) {
+
+		Assert.notNull(aggregationOperations, "AggregationOperations must not be null!");
 		pipeline = new ArrayList<>(aggregationOperations);
 	}
 
@@ -82,30 +86,77 @@ public class AggregationPipeline {
 	 */
 	public boolean isOutOrMerge() {
 
-		if (pipeline.isEmpty()) {
+		if (isEmpty()) {
 			return false;
 		}
 
-		String operator = pipeline.get(pipeline.size() - 1).getOperator();
-		return operator.equals("$out") || operator.equals("$merge");
+		AggregationOperation operation = pipeline.get(pipeline.size() - 1);
+		return isOut(operation) || isMerge(operation);
 	}
 
 	void verify() {
 
 		// check $out/$merge is the last operation if it exists
-		for (AggregationOperation aggregationOperation : pipeline) {
+		for (AggregationOperation operation : pipeline) {
 
-			if (aggregationOperation instanceof OutOperation && !isLast(aggregationOperation)) {
+			if (isOut(operation) && !isLast(operation)) {
 				throw new IllegalArgumentException("The $out operator must be the last stage in the pipeline.");
 			}
 
-			if (aggregationOperation instanceof MergeOperation && !isLast(aggregationOperation)) {
+			if (isMerge(operation) && !isLast(operation)) {
 				throw new IllegalArgumentException("The $merge operator must be the last stage in the pipeline.");
 			}
 		}
 	}
 
+	/**
+	 * Return whether this aggregation pipeline defines a {@code $unionWith} stage that may contribute documents from
+	 * other collections. Checking for presence of union stages is useful when attempting to determine the aggregation
+	 * element type for mapping metadata computation.
+	 *
+	 * @return {@literal true} the aggregation pipeline makes use of {@code $unionWith}.
+	 * @since 3.1
+	 */
+	public boolean containsUnionWith() {
+		return containsOperation(AggregationPipeline::isUnionWith);
+	}
+
+	/**
+	 * @return {@literal true} if the pipeline does not contain any stages.
+	 * @since 3.1
+	 */
+	public boolean isEmpty() {
+		return pipeline.isEmpty();
+	}
+
+	private boolean containsOperation(Predicate<AggregationOperation> predicate) {
+
+		if (isEmpty()) {
+			return false;
+		}
+
+		for (AggregationOperation element : pipeline) {
+			if (predicate.test(element)) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
 	private boolean isLast(AggregationOperation aggregationOperation) {
 		return pipeline.indexOf(aggregationOperation) == pipeline.size() - 1;
 	}
+
+	private static boolean isUnionWith(AggregationOperation operator) {
+		return operator instanceof UnionWithOperation || operator.getOperator().equals("$unionWith");
+	}
+
+	private static boolean isMerge(AggregationOperation operator) {
+		return operator instanceof MergeOperation || operator.getOperator().equals("$merge");
+	}
+
+	private static boolean isOut(AggregationOperation operator) {
+		return operator instanceof OutOperation || operator.getOperator().equals("$out");
+	}
 }

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

@@ -104,7 +104,7 @@ public class BucketOperation extends BucketOperationSupport<BucketOperation, Buc
 		return new Document(getOperator(), options);
 	}
 
-	/* 
+	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#getOperator()
 	 */

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

@@ -1835,7 +1835,7 @@ public class DateOperators {
 		 * @param millisecond must not be {@literal null}.
 		 * @return new instance.
 		 * @throws IllegalArgumentException if given {@literal millisecond} is {@literal null}
-		 * @deprecated since 3.0.7, use {@link #millisecond(Object)} instead.
+		 * @deprecated since 3.2, use {@link #millisecond(Object)} instead.
 		 */
 		@Deprecated
 		default T milliseconds(Object millisecond) {
@@ -1849,7 +1849,7 @@ public class DateOperators {
 		 * @param millisecond must not be {@literal null}.
 		 * @return new instance.
 		 * @throws IllegalArgumentException if given {@literal millisecond} is {@literal null}
-		 * @since 3.0.7
+		 * @since 3.2
 		 */
 		T millisecond(Object millisecond);
 
@@ -1859,7 +1859,7 @@ public class DateOperators {
 		 * @param fieldReference must not be {@literal null}.
 		 * @return new instance.
 		 * @throws IllegalArgumentException if given {@literal fieldReference} is {@literal null}.
-		 * @deprecated since 3.0.7,use {@link #millisecondOf(String)} instead.
+		 * @deprecated since 3.2,use {@link #millisecondOf(String)} instead.
 		 */
 		@Deprecated
 		default T millisecondsOf(String fieldReference) {
@@ -1872,7 +1872,7 @@ public class DateOperators {
 		 * @param fieldReference must not be {@literal null}.
 		 * @return new instance.
 		 * @throws IllegalArgumentException if given {@literal fieldReference} is {@literal null}.
-		 * @since 3.0.7
+		 * @since 3.2
 		 */
 		default T millisecondOf(String fieldReference) {
 			return milliseconds(Fields.field(fieldReference));
@@ -1884,7 +1884,7 @@ public class DateOperators {
 		 * @param expression must not be {@literal null}.
 		 * @return new instance.
 		 * @throws IllegalArgumentException if given {@literal expression} is {@literal null}.
-		 * @deprecated since 3.0.7, use {@link #millisecondOf(AggregationExpression)} instead.
+		 * @deprecated since 3.2, use {@link #millisecondOf(AggregationExpression)} instead.
 		 */
 		@Deprecated
 		default T millisecondsOf(AggregationExpression expression) {
@@ -1897,7 +1897,7 @@ public class DateOperators {
 		 * @param expression must not be {@literal null}.
 		 * @return new instance.
 		 * @throws IllegalArgumentException if given {@literal expression} is {@literal null}.
-		 * @since 3.0.7
+		 * @since 3.2
 		 */
 		default T millisecondOf(AggregationExpression expression) {
 			return milliseconds(expression);

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

@@ -149,4 +149,12 @@ class ExposedFieldsAggregationOperationContext implements AggregationOperationCo
 		}
 		return null;
 	}
+
+	/**
+	 * @return obtain the root context used to resolve references.
+	 * @since 3.1
+	 */
+	AggregationOperationContext getRootContext() {
+		return rootContext;
+	}
 }

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

@@ -23,6 +23,7 @@ import java.util.List;
 import org.bson.Document;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.ExposedField;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.FieldReference;
+import org.springframework.data.mongodb.core.aggregation.ScriptOperators.Accumulator;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -375,6 +376,17 @@ public class GroupOperation implements FieldsExposingAggregationOperation {
 		return newBuilder(GroupOps.STD_DEV_POP, null, expr);
 	}
 
+	/**
+	 * Generates an {@link GroupOperationBuilder} for an {@code $accumulator}-expression.
+	 *
+	 * @param accumulator must not be {@literal null}.
+	 * @return never {@literal null}.
+	 * @since 3.2
+	 */
+	public GroupOperationBuilder accumulate(Accumulator accumulator) {
+		return new GroupOperationBuilder(this, new Operation(accumulator));
+	}
+
 	private GroupOperationBuilder newBuilder(Keyword keyword, @Nullable String reference, @Nullable Object value) {
 		return new GroupOperationBuilder(this, new Operation(keyword, null, reference, value));
 	}
@@ -465,12 +477,16 @@ public class GroupOperation implements FieldsExposingAggregationOperation {
 
 	static class Operation implements AggregationOperation {
 
-		private final Keyword op;
+		private final @Nullable Keyword op;
 		private final @Nullable String key;
 		private final @Nullable String reference;
 		private final @Nullable Object value;
 
-		public Operation(Keyword op, @Nullable String key, @Nullable String reference, @Nullable Object value) {
+		Operation(AggregationExpression expression) {
+			this(null, null, null, expression);
+		}
+
+		public Operation(@Nullable Keyword op, @Nullable String key, @Nullable String reference, @Nullable Object value) {
 
 			this.op = op;
 			this.key = key;
@@ -487,7 +503,12 @@ public class GroupOperation implements FieldsExposingAggregationOperation {
 		}
 
 		public Document toDocument(AggregationOperationContext context) {
-			return new Document(key, new Document(op.toString(), getValue(context)));
+
+			Object value = getValue(context);
+			if(op == null && value instanceof Document) {
+				return new Document(key, value);
+			}
+			return new Document(key, new Document(op.toString(), value));
 		}
 
 		public Object getValue(AggregationOperationContext context) {

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

@@ -52,7 +52,7 @@ public class LimitOperation implements AggregationOperation {
 		return new Document(getOperator(), Long.valueOf(maxElements));
 	}
 
-	/* 
+	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#getOperator()
 	 */

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/ScriptOperators.java

@@ -0,0 +1,587 @@
+/*
+ * Copyright 2020-2021 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.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.springframework.data.mongodb.core.aggregation.ScriptOperators.Accumulator.AccumulatorBuilder;
+import org.springframework.data.mongodb.core.aggregation.ScriptOperators.Accumulator.AccumulatorInitBuilder;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
+
+/**
+ * Gateway to {@literal $function} and {@literal $accumulator} aggregation operations.
+ * <p />
+ * Using {@link ScriptOperators} as part of the {@link Aggregation} requires MongoDB server to have
+ * <a href="https://docs.mongodb.com/master/core/server-side-javascript/">server-side JavaScript</a> execution
+ * <a href="https://docs.mongodb.com/master/reference/configuration-options/#security.javascriptEnabled">enabled</a>.
+ *
+ * @author Christoph Strobl
+ * @author Mark Paluch
+ * @since 3.1
+ */
+public class ScriptOperators {
+
+	/**
+	 * Create a custom aggregation
+	 * <a href="https://docs.mongodb.com/master/reference/operator/aggregation/function/">$function<a /> in JavaScript.
+	 *
+	 * @param body The function definition. Must not be {@literal null}.
+	 * @return new instance of {@link Function}.
+	 */
+	public static Function function(String body) {
+		return Function.function(body);
+	}
+
+	/**
+	 * Create a custom <a href="https://docs.mongodb.com/master/reference/operator/aggregation/accumulator/">$accumulator
+	 * operator</a> in Javascript.
+	 *
+	 * @return new instance of {@link AccumulatorInitBuilder}.
+	 */
+	public static AccumulatorInitBuilder accumulatorBuilder() {
+		return new AccumulatorBuilder();
+	}
+
+	/**
+	 * {@link Function} defines a custom aggregation
+	 * <a href="https://docs.mongodb.com/master/reference/operator/aggregation/function/">$function</a> in JavaScript.
+	 * <p />
+	 * <code class="java">
+	 * {
+	 *   $function: {
+	 *     body: ...,
+	 *     args: ...,
+	 *     lang: "js"
+	 *   }
+	 * }
+	 * </code>
+	 * <p />
+	 * {@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>
+	 * execution must be
+	 * <a href="https://docs.mongodb.com/master/reference/configuration-options/#security.javascriptEnabled">enabled</a>
+	 *
+	 * @see <a href="https://docs.mongodb.com/master/reference/operator/aggregation/function/">MongoDB Documentation:
+	 *      $function</a>
+	 */
+	public static class Function extends AbstractAggregationExpression {
+
+		private Function(Map<String, Object> values) {
+			super(values);
+		}
+
+		/**
+		 * Create a new {@link Function} with the given function definition.
+		 *
+		 * @param body must not be {@literal null}.
+		 * @return new instance of {@link Function}.
+		 */
+		public static Function function(String body) {
+
+			Assert.notNull(body, "Function body must not be null!");
+
+			Map<String, Object> function = new LinkedHashMap<>(2);
+			function.put(Fields.BODY.toString(), body);
+			function.put(Fields.ARGS.toString(), Collections.emptyList());
+			function.put(Fields.LANG.toString(), "js");
+
+			return new Function(function);
+		}
+
+		/**
+		 * Set the arguments passed to the function body.
+		 *
+		 * @param args the arguments passed to the function body. Leave empty if the function does not take any arguments.
+		 * @return new instance of {@link Function}.
+		 */
+		public Function args(Object... args) {
+			return args(Arrays.asList(args));
+		}
+
+		/**
+		 * Set the arguments passed to the function body.
+		 *
+		 * @param args the arguments passed to the function body. Leave empty if the function does not take any arguments.
+		 * @return new instance of {@link Function}.
+		 */
+		public Function args(List<Object> args) {
+
+			Assert.notNull(args, "Args must not be null! Use an empty list instead.");
+
+			return new Function(appendAt(1, Fields.ARGS.toString(), args));
+		}
+
+		/**
+		 * The language used in the body.
+		 *
+		 * @param lang must not be {@literal null} nor empty.
+		 * @return new instance of {@link Function}.
+		 */
+		public Function lang(String lang) {
+
+			Assert.hasText(lang, "Lang must not be null nor empty! The default would be 'js'.");
+
+			return new Function(appendAt(2, Fields.LANG.toString(), lang));
+		}
+
+		@Nullable
+		List<Object> getArgs() {
+			return get(Fields.ARGS.toString());
+		}
+
+		String getBody() {
+			return get(Fields.BODY.toString());
+		}
+
+		String getLang() {
+			return get(Fields.LANG.toString());
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$function";
+		}
+
+		enum Fields {
+
+			BODY, ARGS, LANG;
+
+			@Override
+			public String toString() {
+				return name().toLowerCase();
+			}
+		}
+	}
+
+	/**
+	 * {@link Accumulator} defines a custom aggregation
+	 * <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 />
+	 * <code class="java">
+	 * {
+	 *   $accumulator: {
+	 *     init: ...,
+	 *     intArgs: ...,
+	 *     accumulate: ...,
+	 *     accumulateArgs: ...,
+	 *     merge: ...,
+	 *     finalize: ...,
+	 *     lang: "js"
+	 *   }
+	 * }
+	 * </code>
+	 * <p />
+	 * {@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>
+	 * execution must be
+	 * <a href="https://docs.mongodb.com/master/reference/configuration-options/#security.javascriptEnabled">enabled</a>
+	 *
+	 * @see <a href="https://docs.mongodb.com/master/reference/operator/aggregation/accumulator/">MongoDB Documentation:
+	 *      $accumulator</a>
+	 */
+	public static class Accumulator extends AbstractAggregationExpression {
+
+		private Accumulator(Map<String, Object> value) {
+			super(value);
+		}
+
+		@Override
+		protected String getMongoMethod() {
+			return "$accumulator";
+		}
+
+		enum Fields {
+
+			ACCUMULATE("accumulate"), //
+			ACCUMULATE_ARGS("accumulateArgs"), //
+			FINALIZE("finalize"), //
+			INIT("init"), //
+			INIT_ARGS("initArgs"), //
+			LANG("lang"), //
+			MERGE("merge"); //
+
+			private String field;
+
+			Fields(String field) {
+				this.field = field;
+			}
+
+			@Override
+			public String toString() {
+				return field;
+			}
+		}
+
+		public interface AccumulatorInitBuilder {
+
+			/**
+			 * 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 />
+			 * <code class="java">
+			 * function(initArg1, initArg2, ...) {
+			 *   ...
+			 *   return initialState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return this.
+			 */
+			default AccumulatorAccumulateBuilder init(Function function) {
+				return init(function.getBody()).initArgs(function.getArgs());
+			}
+
+			/**
+			 * 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 />
+			 * <code class="java">
+			 * function(initArg1, initArg2, ...) {
+			 *   ...
+			 *   return initialState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return this.
+			 */
+			AccumulatorInitArgsBuilder init(String function);
+
+			/**
+			 * The language used in the {@code $accumulator} code.
+			 *
+			 * @param lang must not be {@literal null}. Default is {@literal js}.
+			 * @return this.
+			 */
+			AccumulatorInitBuilder lang(String lang);
+		}
+
+		public interface AccumulatorInitArgsBuilder extends AccumulatorAccumulateBuilder {
+
+			/**
+			 * Define the optional {@code initArgs} for the {@link AccumulatorInitBuilder#init(String)} function.
+			 *
+			 * @param args must not be {@literal null}.
+			 * @return this.
+			 */
+			default AccumulatorAccumulateBuilder initArgs(Object... args) {
+				return initArgs(Arrays.asList(args));
+			}
+
+			/**
+			 * Define the optional {@code initArgs} for the {@link AccumulatorInitBuilder#init(String)} function.
+			 *
+			 * @param args must not be {@literal null}.
+			 * @return this.
+			 */
+			AccumulatorAccumulateBuilder initArgs(List<Object> args);
+		}
+
+		public interface AccumulatorAccumulateBuilder {
+
+			/**
+			 * 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 />
+			 * <code class="java">
+			 * function(state, accumArg1, accumArg2, ...) {
+			 *   ...
+			 *   return newState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return this.
+			 */
+			default AccumulatorMergeBuilder accumulate(Function function) {
+				return accumulate(function.getBody()).accumulateArgs(function.getArgs());
+			}
+
+			/**
+			 * 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 />
+			 * <code class="java">
+			 * function(state, accumArg1, accumArg2, ...) {
+			 *   ...
+			 *   return newState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return this.
+			 */
+			AccumulatorAccumulateArgsBuilder accumulate(String function);
+		}
+
+		public interface AccumulatorAccumulateArgsBuilder extends AccumulatorMergeBuilder {
+
+			/**
+			 * Define additional {@code accumulateArgs} for the {@link AccumulatorAccumulateBuilder#accumulate(String)}
+			 * function.
+			 *
+			 * @param args must not be {@literal null}.
+			 * @return this.
+			 */
+			default AccumulatorMergeBuilder accumulateArgs(Object... args) {
+				return accumulateArgs(Arrays.asList(args));
+			}
+
+			/**
+			 * Define additional {@code accumulateArgs} for the {@link AccumulatorAccumulateBuilder#accumulate(String)}
+			 * function.
+			 *
+			 * @param args must not be {@literal null}.
+			 * @return this.
+			 */
+			AccumulatorMergeBuilder accumulateArgs(List<Object> args);
+		}
+
+		public interface AccumulatorMergeBuilder {
+
+			/**
+			 * 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 />
+			 * <code class="java">
+			 * function(state1, state2) {
+			 *   ...
+			 *   return newState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return this.
+			 */
+			AccumulatorFinalizeBuilder merge(String function);
+		}
+
+		public interface AccumulatorFinalizeBuilder {
+
+			/**
+			 * Set the {@code finalize} function used to update the result of the accumulation when all documents have been
+			 * processed.
+			 * <p />
+			 * <code class="java">
+			 * function(state) {
+			 *   ...
+			 *   return finalState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return new instance of {@link Accumulator}.
+			 */
+			Accumulator finalize(String function);
+
+			/**
+			 * Build the {@link Accumulator} object without specifying a {@link #finalize(String) finalize function}.
+			 *
+			 * @return new instance of {@link Accumulator}.
+			 */
+			Accumulator build();
+		}
+
+		static class AccumulatorBuilder
+				implements AccumulatorInitBuilder, AccumulatorInitArgsBuilder, AccumulatorAccumulateBuilder,
+				AccumulatorAccumulateArgsBuilder, AccumulatorMergeBuilder, AccumulatorFinalizeBuilder {
+
+			private List<Object> initArgs;
+			private String initFunction;
+			private List<Object> accumulateArgs;
+			private String accumulateFunction;
+			private String mergeFunction;
+			private String finalizeFunction;
+			private String lang = "js";
+
+			/**
+			 * 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 />
+			 * <code class="java">
+			 * function(initArg1, initArg2, ...) {
+			 *   ...
+			 *   return initialState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return this.
+			 */
+			@Override
+			public AccumulatorBuilder init(String function) {
+
+				this.initFunction = function;
+				return this;
+			}
+
+			/**
+			 * Define the optional {@code initArgs} for the {@link #init(String)} function.
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return this.
+			 */
+			@Override
+			public AccumulatorBuilder initArgs(List<Object> args) {
+
+				Assert.notNull(args, "Args must not be null");
+
+				this.initArgs = new ArrayList<>(args);
+				return this;
+			}
+
+			/**
+			 * 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 />
+			 * <code class="java">
+			 * function(state, accumArg1, accumArg2, ...) {
+			 *   ...
+			 *   return newState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return this.
+			 */
+			@Override
+			public AccumulatorBuilder accumulate(String function) {
+
+				Assert.notNull(function, "Accumulate function must not be null");
+
+				this.accumulateFunction = function;
+				return this;
+			}
+
+			/**
+			 * Define additional {@code accumulateArgs} for the {@link #accumulate(String)} function.
+			 *
+			 * @param args must not be {@literal null}.
+			 * @return this.
+			 */
+			@Override
+			public AccumulatorBuilder accumulateArgs(List<Object> args) {
+
+				Assert.notNull(args, "Args must not be null");
+
+				this.accumulateArgs = new ArrayList<>(args);
+				return this;
+			}
+
+			/**
+			 * 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 />
+			 * <code class="java">
+			 * function(state1, state2) {
+			 *   ...
+			 *   return newState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return this.
+			 */
+			@Override
+			public AccumulatorBuilder merge(String function) {
+
+				Assert.notNull(function, "Merge function must not be null");
+
+				this.mergeFunction = function;
+				return this;
+			}
+
+			/**
+			 * The language used in the {@code $accumulator} code.
+			 *
+			 * @param lang must not be {@literal null}. Default is {@literal js}.
+			 * @return this.
+			 */
+			public AccumulatorBuilder lang(String lang) {
+
+				Assert.hasText(lang, "Lang must not be null nor empty! The default would be 'js'.");
+
+				this.lang = lang;
+				return this;
+			}
+
+			/**
+			 * Set the {@code finalize} function used to update the result of the accumulation when all documents have been
+			 * processed.
+			 * <p />
+			 * <code class="java">
+			 * function(state) {
+			 *   ...
+			 *   return finalState
+			 * }
+			 * </code>
+			 *
+			 * @param function must not be {@literal null}.
+			 * @return new instance of {@link Accumulator}.
+			 */
+			@Override
+			public Accumulator finalize(String function) {
+
+				Assert.notNull(function, "Finalize function must not be null");
+
+				this.finalizeFunction = function;
+
+				Map<String, Object> args = createArgumentMap();
+				args.put(Fields.FINALIZE.toString(), finalizeFunction);
+
+				return new Accumulator(args);
+			}
+
+			@Override
+			public Accumulator build() {
+				return new Accumulator(createArgumentMap());
+			}
+
+			private Map<String, Object> createArgumentMap() {
+
+				Map<String, Object> args = new LinkedHashMap<>();
+				args.put(Fields.INIT.toString(), initFunction);
+				if (!CollectionUtils.isEmpty(initArgs)) {
+					args.put(Fields.INIT_ARGS.toString(), initArgs);
+				}
+				args.put(Fields.ACCUMULATE.toString(), accumulateFunction);
+				if (!CollectionUtils.isEmpty(accumulateArgs)) {
+					args.put(Fields.ACCUMULATE_ARGS.toString(), accumulateArgs);
+				}
+				args.put(Fields.MERGE.toString(), mergeFunction);
+				args.put(Fields.LANG.toString(), lang);
+
+				return args;
+			}
+		}
+	}
+}

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

@@ -78,7 +78,7 @@ public class SortByCountOperation implements AggregationOperation {
 				: groupByExpression.toDocument(context));
 	}
 
-	/* 
+	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#getOperator()
 	 */

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

@@ -21,6 +21,7 @@ import java.util.ArrayList;
 import java.util.List;
 
 import org.bson.Document;
+import org.springframework.data.mapping.PersistentEntity;
 import org.springframework.data.mapping.PersistentPropertyPath;
 import org.springframework.data.mapping.context.MappingContext;
 import org.springframework.data.mongodb.core.aggregation.ExposedFields.DirectFieldReference;
@@ -29,6 +30,7 @@ import org.springframework.data.mongodb.core.aggregation.ExposedFields.FieldRefe
 import org.springframework.data.mongodb.core.convert.QueryMapper;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
+import org.springframework.data.util.Lazy;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 
@@ -46,6 +48,7 @@ public class TypeBasedAggregationOperationContext implements AggregationOperatio
 	private final Class<?> type;
 	private final MappingContext<? extends MongoPersistentEntity<?>, MongoPersistentProperty> mappingContext;
 	private final QueryMapper mapper;
+	private final Lazy<MongoPersistentEntity<?>> entity;
 
 	/**
 	 * Creates a new {@link TypeBasedAggregationOperationContext} for the given type, {@link MappingContext} and
@@ -65,6 +68,7 @@ public class TypeBasedAggregationOperationContext implements AggregationOperatio
 		this.type = type;
 		this.mappingContext = mappingContext;
 		this.mapper = mapper;
+		this.entity = Lazy.of(() -> mappingContext.getPersistentEntity(type));
 	}
 
 	/*
@@ -133,16 +137,37 @@ public class TypeBasedAggregationOperationContext implements AggregationOperatio
 	 */
 	@Override
 	public AggregationOperationContext continueOnMissingFieldReference() {
+		return continueOnMissingFieldReference(type);
+	}
+
+	/**
+	 * This toggle allows the {@link AggregationOperationContext context} to use any given field name without checking for
+	 * its existence. Typically the {@link AggregationOperationContext} fails when referencing unknown fields, those that
+	 * are not present in one of the previous stages or the input source, throughout the pipeline.
+	 *
+	 * @param type The domain type to map fields to.
+	 * @return a more relaxed {@link AggregationOperationContext}.
+	 * @since 3.1
+	 */
+	public AggregationOperationContext continueOnMissingFieldReference(Class<?> type) {
 		return new RelaxedTypeBasedAggregationOperationContext(type, mappingContext, mapper);
 	}
 
 	protected FieldReference getReferenceFor(Field field) {
 
+		if(entity.getNullable() == null) {
+			return new DirectFieldReference(new ExposedField(field, true));
+		}
+
 		PersistentPropertyPath<MongoPersistentProperty> propertyPath = mappingContext
-				.getPersistentPropertyPath(field.getTarget(), type);
+					.getPersistentPropertyPath(field.getTarget(), type);
 		Field mappedField = field(field.getName(),
-				propertyPath.toDotPath(MongoPersistentProperty.PropertyToFieldNameConverter.INSTANCE));
+					propertyPath.toDotPath(MongoPersistentProperty.PropertyToFieldNameConverter.INSTANCE));
 
 		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

@@ -0,0 +1,164 @@
+/*
+ * Copyright 2020-2021 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.Arrays;
+import java.util.List;
+
+import org.bson.Document;
+import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
+
+/**
+ * The <a href="https://docs.mongodb.com/master/reference/operator/aggregation/unionWith/">$unionWith</a> aggregation
+ * stage (available since MongoDB 4.4) performs a union of two collections by combining pipeline results, potentially
+ * 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 />
+ * 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
+ * names to actual field names (considering potential {@link org.springframework.data.mongodb.core.mapping.Field}
+ * annotations) make sure the enclosing aggregation is a {@link TypedAggregation} and provide the target type for the
+ * {@code $unionWith} stage via {@link #mapFieldsTo(Class)}.
+ *
+ * @author Christoph Strobl
+ * @see <a href="https://docs.mongodb.com/master/reference/operator/aggregation/unionWith/">Aggregation Pipeline Stage:
+ *      $unionWith</a>
+ * @since 3.1
+ */
+public class UnionWithOperation implements AggregationOperation {
+
+	private final String collection;
+
+	private final @Nullable AggregationPipeline pipeline;
+
+	private final @Nullable Class<?> domainType;
+
+	public UnionWithOperation(String collection, @Nullable AggregationPipeline pipeline, @Nullable Class<?> domainType) {
+
+		Assert.notNull(collection, "Collection must not be null!");
+
+		this.collection = collection;
+		this.pipeline = pipeline;
+		this.domainType = domainType;
+	}
+
+	/**
+	 * Set the name of the collection from which pipeline results should be included in the result set.<br />
+	 * The collection name is used to set the {@code coll} parameter of {@code $unionWith}.
+	 *
+	 * @param collection the MongoDB collection name. Must not be {@literal null}.
+	 * @return new instance of {@link UnionWithOperation}.
+	 * @throws IllegalArgumentException if the required argument is {@literal null}.
+	 */
+	public static UnionWithOperation unionWith(String collection) {
+		return new UnionWithOperation(collection, null, null);
+	}
+
+	/**
+	 * Set the {@link AggregationPipeline} to apply to the specified collection. The pipeline corresponds to the optional
+	 * {@code pipeline} field of the {@code $unionWith} aggregation stage and is used to compute the documents going into
+	 * the result set.
+	 *
+	 * @param pipeline the {@link AggregationPipeline} that computes the documents. Must not be {@literal null}.
+	 * @return new instance of {@link UnionWithOperation}.
+	 * @throws IllegalArgumentException if the required argument is {@literal null}.
+	 */
+	public UnionWithOperation pipeline(AggregationPipeline pipeline) {
+		return new UnionWithOperation(collection, pipeline, domainType);
+	}
+
+	/**
+	 * Set the aggregation pipeline stages to apply to the specified collection. The pipeline corresponds to the optional
+	 * {@code pipeline} field of the {@code $unionWith} aggregation stage and is used to compute the documents going into
+	 * the result set.
+	 *
+	 * @param aggregationStages the aggregation pipeline stages that compute the documents. Must not be {@literal null}.
+	 * @return new instance of {@link UnionWithOperation}.
+	 * @throws IllegalArgumentException if the required argument is {@literal null}.
+	 */
+	public UnionWithOperation pipeline(List<AggregationOperation> aggregationStages) {
+		return new UnionWithOperation(collection, new AggregationPipeline(aggregationStages), domainType);
+	}
+
+	/**
+	 * Set the aggregation pipeline stages to apply to the specified collection. The pipeline corresponds to the optional
+	 * {@code pipeline} field of the {@code $unionWith} aggregation stage and is used to compute the documents going into
+	 * the result set.
+	 *
+	 * @param aggregationStages the aggregation pipeline stages that compute the documents. Must not be {@literal null}.
+	 * @return new instance of {@link UnionWithOperation}.
+	 * @throws IllegalArgumentException if the required argument is {@literal null}.
+	 */
+	public UnionWithOperation pipeline(AggregationOperation... aggregationStages) {
+		return new UnionWithOperation(collection, new AggregationPipeline(Arrays.asList(aggregationStages)), domainType);
+	}
+
+	/**
+	 * Set domain type used for field name mapping of property references used by the {@link AggregationPipeline}.
+	 * Remember to also use a {@link TypedAggregation} in the outer pipeline.<br />
+	 * If not set, field names used within {@link AggregationOperation pipeline operations} are taken as is.
+	 *
+	 * @param domainType the domain type to map field names used in pipeline operations to. Must not be {@literal null}.
+	 * @return new instance of {@link UnionWithOperation}.
+	 * @throws IllegalArgumentException if the required argument is {@literal null}.
+	 */
+	public UnionWithOperation mapFieldsTo(Class<?> domainType) {
+
+		Assert.notNull(domainType, "DomainType must not be null!");
+		return new UnionWithOperation(collection, pipeline, domainType);
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#toDocument(org.springframework.data.mongodb.core.aggregation.AggregationOperationContext)
+	 */
+	@Override
+	public Document toDocument(AggregationOperationContext context) {
+
+		Document $unionWith = new Document("coll", collection);
+		if (pipeline == null || pipeline.isEmpty()) {
+			return new Document(getOperator(), $unionWith);
+		}
+
+		$unionWith.append("pipeline", pipeline.toDocuments(computeContext(context)));
+		return new Document(getOperator(), $unionWith);
+	}
+
+	private AggregationOperationContext computeContext(AggregationOperationContext source) {
+
+		if (source instanceof TypeBasedAggregationOperationContext) {
+			return ((TypeBasedAggregationOperationContext) source).continueOnMissingFieldReference(domainType != null ? domainType : Object.class);
+		}
+
+		if (source instanceof ExposedFieldsAggregationOperationContext) {
+			return computeContext(((ExposedFieldsAggregationOperationContext) source).getRootContext());
+		}
+
+		return source;
+	}
+
+	/*
+	 * (non-Javadoc)
+	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#getOperator()
+	 */
+	@Override
+	public String getOperator() {
+		return "$unionWith";
+	}
+}

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

@@ -108,7 +108,7 @@ public class UnwindOperation
 		return new Document(getOperator(), unwindArgs);
 	}
 
-	/*
+	/* 
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.aggregation.AggregationOperation#getOperator()
 	 */

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

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.core.convert;
 
 import java.util.Arrays;
 import java.util.Iterator;
+import java.util.Map;
 
 import org.bson.Document;
 import org.bson.conversions.Bson;
@@ -66,6 +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
@@ -119,6 +133,7 @@ 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");
 	}

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

@@ -26,6 +26,7 @@ import org.springframework.data.convert.TypeMapper;
 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.data.util.TypeInformation;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -144,9 +145,9 @@ public interface MongoConverter
 		try {
 			return getConversionService().canConvert(id.getClass(), targetType)
 					? getConversionService().convert(id, targetType)
-					: convertToMongoType(id, null);
+					: convertToMongoType(id, (TypeInformation<?>) null);
 		} catch (ConversionException o_O) {
-			return convertToMongoType(id, null);
+			return convertToMongoType(id,(TypeInformation<?>)  null);
 		}
 	}
 }

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

@@ -27,11 +27,18 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Currency;
 import java.util.List;
+import java.util.UUID;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicLong;
 
+import org.bson.BsonReader;
 import org.bson.BsonTimestamp;
+import org.bson.BsonWriter;
 import org.bson.Document;
+import org.bson.codecs.Codec;
+import org.bson.codecs.DecoderContext;
+import org.bson.codecs.EncoderContext;
+import org.bson.codecs.configuration.CodecRegistries;
 import org.bson.types.Binary;
 import org.bson.types.Code;
 import org.bson.types.Decimal128;
@@ -45,11 +52,12 @@ import org.springframework.data.convert.ReadingConverter;
 import org.springframework.data.convert.WritingConverter;
 import org.springframework.data.mongodb.core.query.Term;
 import org.springframework.data.mongodb.core.script.NamedMongoScript;
-import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.NumberUtils;
 import org.springframework.util.StringUtils;
 
+import com.mongodb.MongoClientSettings;
+
 /**
  * Wrapper class to contain useful converters for the usage with Mongo.
  *
@@ -236,9 +244,27 @@ abstract class MongoConverters {
 
 		INSTANCE;
 
+		private final Codec<Document> codec = CodecRegistries.fromRegistries(CodecRegistries.fromCodecs(new Codec<UUID>() {
+
+			@Override
+			public void encode(BsonWriter writer, UUID value, EncoderContext encoderContext) {
+				writer.writeString(value.toString());
+			}
+
+			@Override
+			public Class<UUID> getEncoderClass() {
+				return UUID.class;
+			}
+
+			@Override
+			public UUID decode(BsonReader reader, DecoderContext decoderContext) {
+				throw new IllegalStateException("decode not supported");
+			}
+		}), MongoClientSettings.getDefaultCodecRegistry()).get(Document.class);
+
 		@Override
 		public String convert(Document source) {
-			return source.toJson();
+			return source.toJson(codec);
 		}
 	}
 
@@ -268,7 +294,7 @@ abstract class MongoConverters {
 		@Override
 		public NamedMongoScript convert(Document source) {
 
-			if(source.isEmpty()) {
+			if (source.isEmpty()) {
 				return null;
 			}
 

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

@@ -40,6 +40,7 @@ import org.springframework.data.mongodb.core.query.MongoRegexCreator;
 import org.springframework.data.mongodb.core.query.MongoRegexCreator.MatchMode;
 import org.springframework.data.mongodb.core.query.SerializationUtils;
 import org.springframework.data.mongodb.core.query.UntypedExampleMatcher;
+import org.springframework.data.mongodb.util.DotPath;
 import org.springframework.data.support.ExampleMatcherAccessor;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.util.Assert;
@@ -134,7 +135,7 @@ public class MongoExampleMapper {
 		while (iter.hasNext()) {
 
 			Map.Entry<String, Object> entry = iter.next();
-			String propertyPath = StringUtils.hasText(path) ? path + "." + entry.getKey() : entry.getKey();
+			String propertyPath = DotPath.from(path).append(entry.getKey()).toString();
 			String mappedPropertyPath = getMappedPropertyPath(propertyPath, probeType);
 
 			if (isEmptyIdProperty(entry)) {

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

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.core.convert;
 
 import org.bson.conversions.Bson;
 import org.springframework.data.convert.EntityWriter;
+import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.lang.Nullable;
@@ -43,7 +44,7 @@ public interface MongoWriter<T> extends EntityWriter<T, Bson> {
 	 */
 	@Nullable
 	default Object convertToMongoType(@Nullable Object obj) {
-		return convertToMongoType(obj, null);
+		return convertToMongoType(obj, (TypeInformation<?>) null);
 	}
 
 	/**
@@ -57,6 +58,9 @@ public interface MongoWriter<T> extends EntityWriter<T, Bson> {
 	@Nullable
 	Object convertToMongoType(@Nullable Object obj, @Nullable TypeInformation<?> typeInformation);
 
+	default Object convertToMongoType(@Nullable Object obj, MongoPersistentEntity<?> entity) {
+		return convertToMongoType(obj, entity.getTypeInformation());
+	}
 	/**
 	 * Creates a {@link DBRef} to refer to the given object.
 	 *

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

@@ -36,12 +36,14 @@ import org.springframework.data.mapping.PropertyPath;
 import org.springframework.data.mapping.PropertyReferenceException;
 import org.springframework.data.mapping.context.InvalidPersistentPropertyPath;
 import org.springframework.data.mapping.context.MappingContext;
+import org.springframework.data.mongodb.MongoExpression;
 import org.springframework.data.mongodb.core.convert.MappingMongoConverter.NestedDocument;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty;
 import org.springframework.data.mongodb.core.mapping.MongoPersistentProperty.PropertyToFieldNameConverter;
 import org.springframework.data.mongodb.core.query.Query;
 import org.springframework.data.mongodb.util.BsonUtils;
+import org.springframework.data.mongodb.util.DotPath;
 import org.springframework.data.util.ClassTypeInformation;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.lang.Nullable;
@@ -140,9 +142,23 @@ public class QueryMapper {
 			try {
 
 				Field field = createPropertyField(entity, key, mappingContext);
-				Entry<String, Object> entry = getMappedObjectForField(field, BsonUtils.get(query, key));
 
-				result.put(entry.getKey(), entry.getValue());
+				// TODO: move to dedicated method
+				if (field.getProperty() != null && field.getProperty().isUnwrapped()) {
+
+					Object theNestedObject = BsonUtils.get(query, key);
+					Document mappedValue = (Document) getMappedValue(field, theNestedObject);
+					if (!StringUtils.hasText(field.getMappedKey())) {
+						result.putAll(mappedValue);
+					} else {
+						result.put(field.getMappedKey(), mappedValue);
+					}
+				} else {
+
+					Entry<String, Object> entry = getMappedObjectForField(field, BsonUtils.get(query, key));
+
+					result.put(entry.getKey(), entry.getValue());
+				}
 			} catch (InvalidPersistentPropertyPath invalidPathException) {
 
 				// in case the object has not already been mapped
@@ -173,10 +189,16 @@ public class QueryMapper {
 			return new Document();
 		}
 
+		sortObject = filterUnwrappedObjects(sortObject, entity);
+
 		Document mappedSort = new Document();
 		for (Map.Entry<String, Object> entry : BsonUtils.asMap(sortObject).entrySet()) {
 
 			Field field = createPropertyField(entity, entry.getKey(), mappingContext);
+			if (field.getProperty() != null && field.getProperty().isUnwrapped()) {
+				continue;
+			}
+
 			mappedSort.put(field.getMappedKey(), entry.getValue());
 		}
 
@@ -197,7 +219,9 @@ public class QueryMapper {
 
 		Assert.notNull(fieldsObject, "FieldsObject must not be null!");
 
-		Document mappedFields = fieldsObject.isEmpty() ? new Document() : getMappedObject(fieldsObject, entity);
+		fieldsObject = filterUnwrappedObjects(fieldsObject, entity);
+
+		Document mappedFields = getMappedObject(fieldsObject, entity);
 		mapMetaAttributes(mappedFields, entity, MetaMapping.FORCE);
 		return mappedFields;
 	}
@@ -217,6 +241,44 @@ public class QueryMapper {
 		}
 	}
 
+	private Document filterUnwrappedObjects(Document fieldsObject, @Nullable MongoPersistentEntity<?> entity) {
+
+		if (fieldsObject.isEmpty() || entity == null) {
+			return fieldsObject;
+		}
+
+		Document target = new Document();
+
+		for (Entry<String, Object> field : fieldsObject.entrySet()) {
+
+			try {
+
+				PropertyPath path = PropertyPath.from(field.getKey(), entity.getTypeInformation());
+				PersistentPropertyPath<MongoPersistentProperty> persistentPropertyPath = mappingContext
+						.getPersistentPropertyPath(path);
+				MongoPersistentProperty property = mappingContext.getPersistentPropertyPath(path).getRequiredLeafProperty();
+
+				if (property.isUnwrapped() && property.isEntity()) {
+
+					MongoPersistentEntity<?> unwrappedEntity = mappingContext.getRequiredPersistentEntity(property);
+
+					for (MongoPersistentProperty unwrappedProperty : unwrappedEntity) {
+
+						DotPath dotPath = DotPath.from(persistentPropertyPath.toDotPath()).append(unwrappedProperty.getName());
+						target.put(dotPath.toString(), field.getValue());
+					}
+
+				} else {
+					target.put(field.getKey(), field.getValue());
+				}
+			} catch (RuntimeException e) {
+				target.put(field.getKey(), field.getValue());
+			}
+
+		}
+		return target;
+	}
+
 	private Document getMappedTextScoreField(MongoPersistentProperty property) {
 		return new Document(property.getFieldName(), META_TEXT_SCORE);
 	}
@@ -233,6 +295,10 @@ public class QueryMapper {
 		String key = field.getMappedKey();
 		Object value;
 
+		if (rawValue instanceof MongoExpression) {
+			return createMapEntry(key, getMappedObject(((MongoExpression) rawValue).toDocument(), field.getEntity()));
+		}
+
 		if (isNestedKeyword(rawValue) && !field.isIdField()) {
 			Keyword keyword = new Keyword((Document) rawValue);
 			value = getMappedKeyword(field, keyword);
@@ -497,6 +563,11 @@ public class QueryMapper {
 	 */
 	@Nullable
 	protected Object delegateConvertToMongoType(Object source, @Nullable MongoPersistentEntity<?> entity) {
+
+		if (entity != null && entity.isUnwrapped()) {
+			return converter.convertToMongoType(source, entity);
+		}
+
 		return converter.convertToMongoType(source, entity == null ? null : entity.getTypeInformation());
 	}
 
@@ -867,6 +938,11 @@ public class QueryMapper {
 			return null;
 		}
 
+		@Nullable
+		MongoPersistentEntity<?> getEntity() {
+			return null;
+		}
+
 		/**
 		 * Returns whether the field represents an association.
 		 *
@@ -912,6 +988,7 @@ public class QueryMapper {
 		public TypeInformation<?> getTypeHint() {
 			return ClassTypeInformation.OBJECT;
 		}
+
 	}
 
 	/**
@@ -1018,6 +1095,12 @@ public class QueryMapper {
 			return property == null ? null : mappingContext.getPersistentEntity(property);
 		}
 
+		@Nullable
+		@Override
+		public MongoPersistentEntity<?> getEntity() {
+			return entity;
+		}
+
 		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.convert.QueryMapper.Field#isAssociation()
@@ -1087,7 +1170,7 @@ public class QueryMapper {
 
 			if (sourceProperty != null && sourceProperty.getOwner().equals(entity)) {
 				return mappingContext
-						.getPersistentPropertyPath(PropertyPath.from(sourceProperty.getName(), entity.getTypeInformation()));
+						.getPersistentPropertyPath(PropertyPath.from(Pattern.quote(sourceProperty.getName()), entity.getTypeInformation()));
 			}
 
 			PropertyPath path = forName(rawPath);
@@ -1146,6 +1229,13 @@ public class QueryMapper {
 					return forName(path.substring(0, path.length() - 3) + "id");
 				}
 
+				// Ok give it another try quoting
+				try {
+					return PropertyPath.from(Pattern.quote(path), entity.getTypeInformation());
+				} catch (PropertyReferenceException | InvalidPersistentPropertyPath ex) {
+
+				}
+
 				return null;
 			}
 		}

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

@@ -132,6 +132,11 @@ public class UpdateMapper extends QueryMapper {
 	 */
 	@Override
 	protected Object delegateConvertToMongoType(Object source, @Nullable MongoPersistentEntity<?> entity) {
+
+		if(entity != null && entity.isUnwrapped()) {
+			return converter.convertToMongoType(source, entity);
+		}
+
 		return converter.convertToMongoType(source,
 				entity == null ? ClassTypeInformation.OBJECT : getTypeHintForEntity(source, entity));
 	}

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

@@ -16,7 +16,7 @@
 package org.springframework.data.mongodb.core.geo;
 
 /**
- * Interface definition for structures defined in <a href="https://geojson.org/">GeoJSON</a> format.
+ * Interface definition for structures defined in <a href="https://geojson.org/>GeoJSON</a> format.
  *
  * @author Christoph Strobl
  * @since 1.7

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

@@ -24,7 +24,7 @@ import org.springframework.data.geo.Point;
 import org.springframework.lang.Nullable;
 
 import com.fasterxml.jackson.core.JsonParser;
-import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.core.Version;
 import com.fasterxml.jackson.databind.DeserializationContext;
 import com.fasterxml.jackson.databind.JsonDeserializer;
 import com.fasterxml.jackson.databind.JsonNode;
@@ -34,7 +34,10 @@ import com.fasterxml.jackson.databind.module.SimpleModule;
 import com.fasterxml.jackson.databind.node.ArrayNode;
 
 /**
- * A Jackson {@link Module} to register custom {@link JsonSerializer} and {@link JsonDeserializer}s for GeoJSON types.
+ * A Jackson {@link Module} to register custom {@link JsonDeserializer}s for GeoJSON types.
+ * <p />
+ * Use {@link #geoJsonModule()} to obtain a {@link Module} containing both {@link JsonSerializer serializers} and
+ * {@link JsonDeserializer deserializers}.
  *
  * @author Christoph Strobl
  * @author Oliver Gierke
@@ -47,12 +50,87 @@ public class GeoJsonModule extends SimpleModule {
 
 	public GeoJsonModule() {
 
-		addDeserializer(GeoJsonPoint.class, new GeoJsonPointDeserializer());
-		addDeserializer(GeoJsonMultiPoint.class, new GeoJsonMultiPointDeserializer());
-		addDeserializer(GeoJsonLineString.class, new GeoJsonLineStringDeserializer());
-		addDeserializer(GeoJsonMultiLineString.class, new GeoJsonMultiLineStringDeserializer());
-		addDeserializer(GeoJsonPolygon.class, new GeoJsonPolygonDeserializer());
-		addDeserializer(GeoJsonMultiPolygon.class, new GeoJsonMultiPolygonDeserializer());
+		registerDeserializersIn(this);
+		// TODO: add serializers as of next major version (4.0).
+	}
+
+	/**
+	 * Obtain a {@link Module} containing {@link JsonDeserializer deserializers} for the following {@link GeoJson} types:
+	 * <ul>
+	 * <li>{@link GeoJsonPoint}</li>
+	 * <li>{@link GeoJsonMultiPoint}</li>
+	 * <li>{@link GeoJsonLineString}</li>
+	 * <li>{@link GeoJsonMultiLineString}</li>
+	 * <li>{@link GeoJsonPolygon}</li>
+	 * <li>{@link GeoJsonMultiPolygon}</li>
+	 * </ul>
+	 *
+	 * @return a {@link Module} containing {@link JsonDeserializer deserializers} for {@link GeoJson} types.
+	 * @since 3.2
+	 */
+	public static Module deserializers() {
+
+		SimpleModule module = new SimpleModule("Spring Data MongoDB GeoJson - Deserializers",
+				new Version(3, 2, 0, null, "org.springframework.data", "spring-data-mongodb-geojson"));
+		registerDeserializersIn(module);
+		return module;
+	}
+
+	/**
+	 * Obtain a {@link Module} containing {@link JsonSerializer serializers} for the following {@link GeoJson} types:
+	 * <ul>
+	 * <li>{@link GeoJsonPoint}</li>
+	 * <li>{@link GeoJsonMultiPoint}</li>
+	 * <li>{@link GeoJsonLineString}</li>
+	 * <li>{@link GeoJsonMultiLineString}</li>
+	 * <li>{@link GeoJsonPolygon}</li>
+	 * <li>{@link GeoJsonMultiPolygon}</li>
+	 * </ul>
+	 *
+	 * @return a {@link Module} containing {@link JsonSerializer serializers} for {@link GeoJson} types.
+	 * @since 3.2
+	 */
+	public static Module serializers() {
+
+		SimpleModule module = new SimpleModule("Spring Data MongoDB GeoJson - Serializers",
+				new Version(3, 2, 0, null, "org.springframework.data", "spring-data-mongodb-geojson"));
+		GeoJsonSerializersModule.registerSerializersIn(module);
+		return module;
+	}
+
+	/**
+	 * Obtain a {@link Module} containing {@link JsonSerializer serializers} and {@link JsonDeserializer deserializers}
+	 * for the following {@link GeoJson} types:
+	 * <ul>
+	 * <li>{@link GeoJsonPoint}</li>
+	 * <li>{@link GeoJsonMultiPoint}</li>
+	 * <li>{@link GeoJsonLineString}</li>
+	 * <li>{@link GeoJsonMultiLineString}</li>
+	 * <li>{@link GeoJsonPolygon}</li>
+	 * <li>{@link GeoJsonMultiPolygon}</li>
+	 * </ul>
+	 *
+	 * @return a {@link Module} containing {@link JsonSerializer serializers} and {@link JsonDeserializer deserializers}
+	 *         for {@link GeoJson} types.
+	 * @since 3.2
+	 */
+	public static Module geoJsonModule() {
+
+		SimpleModule module = new SimpleModule("Spring Data MongoDB GeoJson",
+				new Version(3, 2, 0, null, "org.springframework.data", "spring-data-mongodb-geojson"));
+		GeoJsonSerializersModule.registerSerializersIn(module);
+		registerDeserializersIn(module);
+		return module;
+	}
+
+	private static void registerDeserializersIn(SimpleModule module) {
+
+		module.addDeserializer(GeoJsonPoint.class, new GeoJsonPointDeserializer());
+		module.addDeserializer(GeoJsonMultiPoint.class, new GeoJsonMultiPointDeserializer());
+		module.addDeserializer(GeoJsonLineString.class, new GeoJsonLineStringDeserializer());
+		module.addDeserializer(GeoJsonMultiLineString.class, new GeoJsonMultiLineStringDeserializer());
+		module.addDeserializer(GeoJsonPolygon.class, new GeoJsonPolygonDeserializer());
+		module.addDeserializer(GeoJsonMultiPolygon.class, new GeoJsonMultiPolygonDeserializer());
 	}
 
 	/**
@@ -67,8 +145,7 @@ public class GeoJsonModule extends SimpleModule {
 		 */
 		@Nullable
 		@Override
-		public T deserialize(@Nullable JsonParser jp, @Nullable DeserializationContext ctxt)
-				throws IOException, JsonProcessingException {
+		public T deserialize(@Nullable JsonParser jp, @Nullable DeserializationContext ctxt) throws IOException {
 
 			JsonNode node = jp.readValueAsTree();
 			JsonNode coordinates = node.get("coordinates");
@@ -134,7 +211,7 @@ public class GeoJsonModule extends SimpleModule {
 				return Collections.emptyList();
 			}
 
-			List<Point> points = new ArrayList<Point>(node.size());
+			List<Point> points = new ArrayList<>(node.size());
 
 			for (JsonNode coordinatePair : node) {
 				if (coordinatePair.isArray()) {
@@ -145,7 +222,7 @@ public class GeoJsonModule extends SimpleModule {
 		}
 
 		protected GeoJsonLineString toLineString(ArrayNode node) {
-			return new GeoJsonLineString(toPoints((ArrayNode) node));
+			return new GeoJsonLineString(toPoints(node));
 		}
 	}
 
@@ -259,7 +336,7 @@ public class GeoJsonModule extends SimpleModule {
 		@Override
 		protected GeoJsonMultiLineString doDeserialize(ArrayNode coordinates) {
 
-			List<GeoJsonLineString> lines = new ArrayList<GeoJsonLineString>(coordinates.size());
+			List<GeoJsonLineString> lines = new ArrayList<>(coordinates.size());
 
 			for (JsonNode lineString : coordinates) {
 				if (lineString.isArray()) {
@@ -336,7 +413,7 @@ public class GeoJsonModule extends SimpleModule {
 		@Override
 		protected GeoJsonMultiPolygon doDeserialize(ArrayNode coordinates) {
 
-			List<GeoJsonPolygon> polygones = new ArrayList<GeoJsonPolygon>(coordinates.size());
+			List<GeoJsonPolygon> polygones = new ArrayList<>(coordinates.size());
 
 			for (JsonNode polygon : coordinates) {
 				for (JsonNode ring : polygon) {

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

@@ -0,0 +1,313 @@
+/*
+ * 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.geo;
+
+import java.io.IOException;
+
+import org.springframework.data.geo.Point;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.JsonSerializer;
+import com.fasterxml.jackson.databind.Module;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.module.SimpleModule;
+
+/**
+ * A Jackson {@link Module} to register custom {@link JsonSerializer}s for GeoJSON types.
+ *
+ * @author Bjorn Harvold
+ * @author Christoph Strobl
+ * @since 3.2
+ */
+class GeoJsonSerializersModule extends SimpleModule {
+
+	private static final long serialVersionUID = 1340494654898895610L;
+
+	GeoJsonSerializersModule() {
+		registerSerializersIn(this);
+	}
+
+
+	static void registerSerializersIn(SimpleModule module) {
+
+		module.addSerializer(GeoJsonPoint.class, new GeoJsonPointSerializer());
+		module.addSerializer(GeoJsonMultiPoint.class, new GeoJsonMultiPointSerializer());
+		module.addSerializer(GeoJsonLineString.class, new GeoJsonLineStringSerializer());
+		module.addSerializer(GeoJsonMultiLineString.class, new GeoJsonMultiLineStringSerializer());
+		module.addSerializer(GeoJsonPolygon.class, new GeoJsonPolygonSerializer());
+		module.addSerializer(GeoJsonMultiPolygon.class, new GeoJsonMultiPolygonSerializer());
+	}
+
+	/**
+	 * @param <T>
+	 * @author Christoph Strobl
+	 */
+	private static abstract class GeoJsonSerializer<T extends GeoJson<? extends Iterable>> extends JsonSerializer<T> {
+
+		/*
+		 * (non-Javadoc)
+		 * @see com.fasterxml.jackson.databind.JsonSerializer#serialize(java.lang.Object, com.fasterxml.jackson.core.JsonGenerator, com.fasterxml.jackson.databind.SerializerProvider)
+		 */
+		@Override
+		public void serialize(T shape, JsonGenerator jsonGenerator, SerializerProvider serializers) throws IOException {
+
+			jsonGenerator.writeStartObject();
+			jsonGenerator.writeStringField("type", shape.getType());
+			jsonGenerator.writeArrayFieldStart("coordinates");
+
+			doSerialize(shape, jsonGenerator);
+
+			jsonGenerator.writeEndArray();
+			jsonGenerator.writeEndObject();
+		}
+
+		/**
+		 * Perform the actual serialization given the {@literal shape} as {@link GeoJson}.
+		 *
+		 * @param shape
+		 * @param jsonGenerator
+		 * @return
+		 */
+		protected abstract void doSerialize(T shape, JsonGenerator jsonGenerator) throws IOException;
+
+		/**
+		 * Write a {@link Point} as array. <br />
+		 * {@code [10.0, 20.0]}
+		 *
+		 * @param point
+		 * @param jsonGenerator
+		 * @throws IOException
+		 */
+		protected void writePoint(Point point, JsonGenerator jsonGenerator) throws IOException {
+
+			jsonGenerator.writeStartArray();
+			writeRawCoordinates(point, jsonGenerator);
+			jsonGenerator.writeEndArray();
+		}
+
+		/**
+		 * Write the {@link Point} coordinates. <br />
+		 * {@code 10.0, 20.0}
+		 *
+		 * @param point
+		 * @param jsonGenerator
+		 * @throws IOException
+		 */
+		protected void writeRawCoordinates(Point point, JsonGenerator jsonGenerator) throws IOException {
+
+			jsonGenerator.writeNumber(point.getX());
+			jsonGenerator.writeNumber(point.getY());
+		}
+
+		/**
+		 * Write an {@link Iterable} of {@link Point} as array. <br />
+		 * {@code [ [10.0, 20.0], [30.0, 40.0], [50.0, 60.0] ]}
+		 *
+		 * @param points
+		 * @param jsonGenerator
+		 * @throws IOException
+		 */
+		protected void writeLine(Iterable<Point> points, JsonGenerator jsonGenerator) throws IOException {
+
+			jsonGenerator.writeStartArray();
+			writeRawLine(points, jsonGenerator);
+			jsonGenerator.writeEndArray();
+		}
+
+		/**
+		 * Write an {@link Iterable} of {@link Point}. <br />
+		 * {@code [10.0, 20.0], [30.0, 40.0], [50.0, 60.0]}
+		 *
+		 * @param points
+		 * @param jsonGenerator
+		 * @throws IOException
+		 */
+		protected void writeRawLine(Iterable<Point> points, JsonGenerator jsonGenerator) throws IOException {
+
+			for (Point point : points) {
+				writePoint(point, jsonGenerator);
+			}
+		}
+	}
+
+	/**
+	 * {@link JsonSerializer} converting {@link GeoJsonPoint} to:
+	 *
+	 * <pre>
+	 * <code>
+	 * { "type": "Point", "coordinates": [10.0, 20.0] }
+	 * </code>
+	 * </pre>
+	 *
+	 * @author Bjorn Harvold
+	 * @author Christoph Strobl
+	 * @since 3.2
+	 */
+	static class GeoJsonPointSerializer extends GeoJsonSerializer<GeoJsonPoint> {
+
+		@Override
+		protected void doSerialize(GeoJsonPoint value, JsonGenerator jsonGenerator) throws IOException {
+			writeRawCoordinates(value, jsonGenerator);
+		}
+	}
+
+	/**
+	 * {@link JsonSerializer} converting {@link GeoJsonLineString} to:
+	 *
+	 * <pre>
+	 * <code>
+	 * {
+	 *   "type": "LineString",
+	 *   "coordinates": [
+	 *     [10.0, 20.0], [30.0, 40.0], [50.0, 60.0]
+	 *   ]
+	 * }
+	 * </code>
+	 * </pre>
+	 *
+	 * @author Bjorn Harvold
+	 * @author Christoph Strobl
+	 * @since 3.2
+	 */
+	static class GeoJsonLineStringSerializer extends GeoJsonSerializer<GeoJsonLineString> {
+
+		@Override
+		protected void doSerialize(GeoJsonLineString value, JsonGenerator jsonGenerator) throws IOException {
+			writeRawLine(value.getCoordinates(), jsonGenerator);
+		}
+	}
+
+	/**
+	 * {@link JsonSerializer} converting {@link GeoJsonMultiPoint} to:
+	 *
+	 * <pre>
+	 * <code>
+	 * {
+	 *   "type": "MultiPoint",
+	 *   "coordinates": [
+	 *     [10.0, 20.0], [30.0, 40.0], [50.0, 60.0]
+	 *   ]
+	 * }
+	 * </code>
+	 * </pre>
+	 *
+	 * @author Bjorn Harvold
+	 * @author Christoph Strobl
+	 * @since 3.2
+	 */
+	static class GeoJsonMultiPointSerializer extends GeoJsonSerializer<GeoJsonMultiPoint> {
+
+		@Override
+		protected void doSerialize(GeoJsonMultiPoint value, JsonGenerator jsonGenerator) throws IOException {
+			writeRawLine(value.getCoordinates(), jsonGenerator);
+		}
+	}
+
+	/**
+	 * {@link JsonSerializer} converting {@link GeoJsonMultiLineString} to:
+	 *
+	 * <pre>
+	 * <code>
+	 * {
+	 *   "type": "MultiLineString",
+	 *   "coordinates": [
+	 *     [ [10.0, 20.0], [30.0, 40.0] ],
+	 *     [ [50.0, 60.0] , [70.0, 80.0] ]
+	 *   ]
+	 * }
+	 * </code>
+	 * </pre>
+	 *
+	 * @author Bjorn Harvold
+	 * @author Christoph Strobl
+	 * @since 3.2
+	 */
+	static class GeoJsonMultiLineStringSerializer extends GeoJsonSerializer<GeoJsonMultiLineString> {
+
+		@Override
+		protected void doSerialize(GeoJsonMultiLineString value, JsonGenerator jsonGenerator) throws IOException {
+
+			for (GeoJsonLineString lineString : value.getCoordinates()) {
+				writeLine(lineString.getCoordinates(), jsonGenerator);
+			}
+		}
+	}
+
+	/**
+	 * {@link JsonSerializer} converting {@link GeoJsonPolygon} to:
+	 *
+	 * <pre>
+	 * <code>
+	 * {
+	 *   "type": "Polygon",
+	 *   "coordinates": [
+	 *     [ [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0] ]
+	 *   ]
+	 * }
+	 * </code>
+	 * </pre>
+	 *
+	 * @author Bjorn Harvold
+	 * @author Christoph Strobl
+	 * @since 3.2
+	 */
+	static class GeoJsonPolygonSerializer extends GeoJsonSerializer<GeoJsonPolygon> {
+
+		@Override
+		protected void doSerialize(GeoJsonPolygon value, JsonGenerator jsonGenerator) throws IOException {
+
+			for (GeoJsonLineString lineString : value.getCoordinates()) {
+				writeLine(lineString.getCoordinates(), jsonGenerator);
+			}
+		}
+	}
+
+	/**
+	 * {@link JsonSerializer} converting {@link GeoJsonMultiPolygon} to:
+	 *
+	 * <pre>
+	 * <code>
+	 * {
+	 *   "type": "MultiPolygon",
+	 *   "coordinates": [
+	 *     [[[102.0, 2.0], [103.0, 2.0], [103.0, 3.0], [102.0, 3.0], [102.0, 2.0]]],
+	 *     [[[100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0]],
+	 *     [[100.2, 0.2], [100.8, 0.2], [100.8, 0.8], [100.2, 0.8], [100.2, 0.2]]]
+	 *   ]
+	 * }
+	 * </code>
+	 * </pre>
+	 *
+	 * @author Bjorn Harvold
+	 * @author Christoph Strobl
+	 * @since 3.2
+	 */
+	static class GeoJsonMultiPolygonSerializer extends GeoJsonSerializer<GeoJsonMultiPolygon> {
+
+		@Override
+		protected void doSerialize(GeoJsonMultiPolygon value, JsonGenerator jsonGenerator) throws IOException {
+
+			for (GeoJsonPolygon polygon : value.getCoordinates()) {
+
+				jsonGenerator.writeStartArray();
+				for (GeoJsonLineString lineString : polygon.getCoordinates()) {
+					writeLine(lineString.getCoordinates(), jsonGenerator);
+				}
+				jsonGenerator.writeEndArray();
+			}
+		}
+	}
+}

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

@@ -46,6 +46,7 @@ import java.lang.annotation.Target;
  * @author Philipp Schneider
  * @author Johno Crawford
  * @author Christoph Strobl
+ * @author Dave Perryman
  */
 @Target({ ElementType.TYPE })
 @Documented
@@ -95,7 +96,8 @@ public @interface CompoundIndex {
 	boolean unique() default false;
 
 	/**
-	 * If set to true index will skip over any document that is missing the indexed field.
+	 * If set to true index will skip over any document that is missing the indexed field. <br />
+	 * Must not be used with {@link #partialFilter()}.
 	 *
 	 * @return {@literal false} by default.
 	 * @see <a href=
@@ -170,4 +172,14 @@ public @interface CompoundIndex {
 	 */
 	boolean background() default false;
 
+	/**
+	 * Only index the documents in a collection that meet a specified {@link IndexFilter filter expression}. <br />
+	 * Must not be used with {@link #sparse() sparse = true}.
+	 *
+	 * @return empty by default.
+	 * @see <a href=
+	 *      "https://docs.mongodb.com/manual/core/index-partial/">https://docs.mongodb.com/manual/core/index-partial/</a>
+	 * @since 3.1
+	 */
+	String partialFilter() default "";
 }

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

@@ -15,6 +15,8 @@
  */
 package org.springframework.data.mongodb.core.index;
 
+import org.springframework.lang.Nullable;
+
 /**
  * Provider interface to obtain {@link IndexOperations} by MongoDB collection name.
  *
@@ -26,10 +28,22 @@ package org.springframework.data.mongodb.core.index;
 public interface IndexOperationsProvider {
 
 	/**
-	 * Returns the operations that can be performed on indexes
+	 * Returns the operations that can be performed on indexes.
 	 *
 	 * @param collectionName name of the MongoDB collection, must not be {@literal null}.
 	 * @return index operations on the named collection
 	 */
-	IndexOperations indexOps(String collectionName);
+	default IndexOperations indexOps(String collectionName) {
+		return indexOps(collectionName, null);
+	}
+
+	/**
+	 * Returns the operations that can be performed on indexes.
+	 *
+	 * @param collectionName name of the MongoDB collection, must not be {@literal null}.
+	 * @param type the type used for field mapping. Can be {@literal null}.
+	 * @return index operations on the named collection
+	 * @since 3.2
+	 */
+	IndexOperations indexOps(String collectionName, @Nullable Class<?> type);
 }

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

@@ -53,7 +53,8 @@ public @interface Indexed {
 	IndexDirection direction() default IndexDirection.ASCENDING;
 
 	/**
-	 * If set to true index will skip over any document that is missing the indexed field.
+	 * If set to true index will skip over any document that is missing the indexed field. <br />
+	 * Must not be used with {@link #partialFilter()}.
 	 *
 	 * @return {@literal false} by default.
 	 * @see <a href=
@@ -170,4 +171,15 @@ public @interface Indexed {
 	 * @since 2.2
 	 */
 	String expireAfter() default "";
+
+	/**
+	 * Only index the documents in a collection that meet a specified {@link IndexFilter filter expression}. <br />
+	 * Must not be used with {@link #sparse() sparse = true}.
+	 *
+	 * @return empty by default.
+	 * @see <a href=
+	 *      "https://docs.mongodb.com/manual/core/index-partial/">https://docs.mongodb.com/manual/core/index-partial/</a>
+	 * @since 3.1
+	 */
+	String partialFilter() default "";
 }

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

@@ -15,10 +15,6 @@
  */
 package org.springframework.data.mongodb.core.index;
 
-import lombok.AccessLevel;
-import lombok.EqualsAndHashCode;
-import lombok.RequiredArgsConstructor;
-
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -33,7 +29,6 @@ import java.util.stream.Collectors;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
 import org.springframework.dao.InvalidDataAccessApiUsageException;
 import org.springframework.data.domain.Sort;
 import org.springframework.data.mapping.Association;
@@ -51,6 +46,8 @@ import org.springframework.data.mongodb.core.mapping.BasicMongoPersistentEntity;
 import org.springframework.data.mongodb.core.mapping.Document;
 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.data.mongodb.util.DotPath;
 import org.springframework.data.spel.EvaluationContextProvider;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.expression.EvaluationContext;
@@ -74,6 +71,7 @@ import org.springframework.util.StringUtils;
  * @author Thomas Darimont
  * @author Martin Macko
  * @author Mark Paluch
+ * @author Dave Perryman
  * @since 1.5
  */
 public class MongoPersistentEntityIndexResolver implements IndexResolver {
@@ -138,8 +136,9 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 
 		try {
 			if (persistentProperty.isEntity()) {
-				indexes.addAll(resolveIndexForClass(persistentProperty.getTypeInformation().getActualType(),
-						persistentProperty.getFieldName(), Path.of(persistentProperty), root.getCollection(), guard));
+				indexes.addAll(resolveIndexForEntity(mappingContext.getPersistentEntity(persistentProperty),
+						persistentProperty.isUnwrapped() ? "" : persistentProperty.getFieldName(), Path.of(persistentProperty),
+						root.getCollection(), guard));
 			}
 
 			List<IndexDefinitionHolder> indexDefinitions = createIndexDefinitionHolderForProperty(
@@ -163,12 +162,16 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 	 * @return List of {@link IndexDefinitionHolder} representing indexes for given type and its referenced property
 	 *         types. Will never be {@code null}.
 	 */
-	private List<IndexDefinitionHolder> resolveIndexForClass(final TypeInformation<?> type, final String dotPath,
-			final Path path, final String collection, final CycleGuard guard) {
+	private List<IndexDefinitionHolder> resolveIndexForClass( TypeInformation<?> type,  String dotPath,
+			 Path path,  String collection,  CycleGuard guard) {
 
-		MongoPersistentEntity<?> entity = mappingContext.getRequiredPersistentEntity(type);
+		return resolveIndexForEntity(mappingContext.getRequiredPersistentEntity(type), dotPath, path, collection, guard);
+	}
 
-		final List<IndexDefinitionHolder> indexInformation = new ArrayList<>();
+	private List<IndexDefinitionHolder> resolveIndexForEntity(MongoPersistentEntity<?> entity,  String dotPath,
+			 Path path,  String collection,  CycleGuard guard) {
+
+		List<IndexDefinitionHolder> indexInformation = new ArrayList<>();
 		indexInformation.addAll(potentiallyCreateCompoundIndexDefinitions(dotPath, collection, entity));
 
 		entity.doWithProperties((PropertyHandler<MongoPersistentProperty>) property -> this
@@ -182,21 +185,25 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 	private void guardAndPotentiallyAddIndexForProperty(MongoPersistentProperty persistentProperty, String dotPath,
 			Path path, String collection, List<IndexDefinitionHolder> indexes, CycleGuard guard) {
 
-		String propertyDotPath = (StringUtils.hasText(dotPath) ? dotPath + "." : "") + persistentProperty.getFieldName();
+		DotPath propertyDotPath = DotPath.from(dotPath);
+
+		if (!persistentProperty.isUnwrapped()) {
+			propertyDotPath = propertyDotPath.append(persistentProperty.getFieldName());
+		}
 
 		Path propertyPath = path.append(persistentProperty);
 		guard.protect(persistentProperty, propertyPath);
 
 		if (persistentProperty.isEntity()) {
 			try {
-				indexes.addAll(resolveIndexForClass(persistentProperty.getTypeInformation().getActualType(), propertyDotPath,
+				indexes.addAll(resolveIndexForEntity(mappingContext.getPersistentEntity(persistentProperty), propertyDotPath.toString(),
 						propertyPath, collection, guard));
 			} catch (CyclicPropertyReferenceException e) {
 				LOGGER.info(e.getMessage());
 			}
 		}
 
-		List<IndexDefinitionHolder> indexDefinitions = createIndexDefinitionHolderForProperty(propertyDotPath, collection,
+		List<IndexDefinitionHolder> indexDefinitions = createIndexDefinitionHolderForProperty(propertyDotPath.toString(), collection,
 				persistentProperty);
 
 		if (!indexDefinitions.isEmpty()) {
@@ -209,6 +216,13 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 
 		List<IndexDefinitionHolder> indices = new ArrayList<>(2);
 
+		if (persistentProperty.isUnwrapped() && (persistentProperty.isAnnotationPresent(Indexed.class)
+				|| persistentProperty.isAnnotationPresent(HashIndexed.class)
+				|| persistentProperty.isAnnotationPresent(GeoSpatialIndexed.class))) {
+			throw new InvalidDataAccessApiUsageException(
+					String.format("Index annotation not allowed on unwrapped object for path '%s'.", dotPath));
+		}
+
 		if (persistentProperty.isAnnotationPresent(Indexed.class)) {
 			indices.add(createIndexDefinition(dotPath, collection, persistentProperty));
 		} else if (persistentProperty.isAnnotationPresent(GeoSpatialIndexed.class)) {
@@ -257,7 +271,7 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 		}
 
 		try {
-			appendTextIndexInformation("", Path.empty(), indexDefinitionBuilder, root,
+			appendTextIndexInformation(DotPath.empty(), Path.empty(), indexDefinitionBuilder, root,
 					new TextIndexIncludeOptions(IncludeStrategy.DEFAULT), new CycleGuard());
 		} catch (CyclicPropertyReferenceException e) {
 			LOGGER.info(e.getMessage());
@@ -278,9 +292,9 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 
 	}
 
-	private void appendTextIndexInformation(final String dotPath, final Path path,
-			final TextIndexDefinitionBuilder indexDefinitionBuilder, final MongoPersistentEntity<?> entity,
-			final TextIndexIncludeOptions includeOptions, final CycleGuard guard) {
+	private void appendTextIndexInformation(DotPath dotPath, Path path,
+			TextIndexDefinitionBuilder indexDefinitionBuilder, MongoPersistentEntity<?> entity,
+			TextIndexIncludeOptions includeOptions, CycleGuard guard) {
 
 		entity.doWithProperties(new PropertyHandler<MongoPersistentProperty>() {
 
@@ -289,7 +303,7 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 
 				guard.protect(persistentProperty, path);
 
-				if (persistentProperty.isExplicitLanguageProperty() && !StringUtils.hasText(dotPath)) {
+				if (persistentProperty.isExplicitLanguageProperty() && dotPath.isEmpty()) {
 					indexDefinitionBuilder.withLanguageOverride(persistentProperty.getFieldName());
 				}
 
@@ -297,8 +311,8 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 
 				if (includeOptions.isForce() || indexed != null || persistentProperty.isEntity()) {
 
-					String propertyDotPath = (StringUtils.hasText(dotPath) ? dotPath + "." : "")
-							+ persistentProperty.getFieldName();
+					DotPath propertyDotPath = dotPath
+							.append(persistentProperty.getFieldName());
 
 					Path propertyPath = path.append(persistentProperty);
 
@@ -311,7 +325,7 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 						TextIndexIncludeOptions optionsForNestedType = includeOptions;
 						if (!IncludeStrategy.FORCE.equals(includeOptions.getStrategy()) && indexed != null) {
 							optionsForNestedType = new TextIndexIncludeOptions(IncludeStrategy.FORCE,
-									new TextIndexedFieldSpec(propertyDotPath, weight));
+									new TextIndexedFieldSpec(propertyDotPath.toString(), weight));
 						}
 
 						try {
@@ -324,7 +338,7 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 									entity.getName()), e);
 						}
 					} else if (includeOptions.isForce() || indexed != null) {
-						indexDefinitionBuilder.onField(propertyDotPath, weight);
+						indexDefinitionBuilder.onField(propertyDotPath.toString(), weight);
 					}
 				}
 
@@ -385,6 +399,10 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 			indexDefinition.background();
 		}
 
+		if (StringUtils.hasText(index.partialFilter())) {
+			indexDefinition.partial(evaluatePartialFilter(index.partialFilter(), entity));
+		}
+
 		return new IndexDefinitionHolder(dotPath, indexDefinition, collection);
 	}
 
@@ -474,9 +492,24 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 			}
 		}
 
+		if (StringUtils.hasText(index.partialFilter())) {
+			indexDefinition.partial(evaluatePartialFilter(index.partialFilter(), persistentProperty.getOwner()));
+		}
+
 		return new IndexDefinitionHolder(dotPath, indexDefinition, collection);
 	}
 
+	private PartialIndexFilter evaluatePartialFilter(String filterExpression, PersistentEntity<?, ?> entity) {
+
+		Object result = evaluate(filterExpression, getEvaluationContextForProperty(entity));
+
+		if (result instanceof org.bson.Document) {
+			return PartialIndexFilter.of((org.bson.Document) result);
+		}
+
+		return PartialIndexFilter.of(BsonUtils.parse(filterExpression, null));
+	}
+
 	/**
 	 * Creates {@link HashedIndex} wrapped in {@link IndexDefinitionHolder} out of {@link HashIndexed} for a given
 	 * {@link MongoPersistentProperty}.
@@ -616,7 +649,7 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 
 		MongoPersistentProperty property = association.getInverse();
 
-		String propertyDotPath = (StringUtils.hasText(path) ? path + "." : "") + property.getFieldName();
+		DotPath propertyDotPath = DotPath.from(path).append(property.getFieldName());
 
 		if (property.isAnnotationPresent(GeoSpatialIndexed.class) || property.isAnnotationPresent(TextIndexed.class)) {
 			throw new MappingException(
@@ -624,7 +657,7 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 							propertyDotPath));
 		}
 
-		List<IndexDefinitionHolder> indexDefinitions = createIndexDefinitionHolderForProperty(propertyDotPath, collection,
+		List<IndexDefinitionHolder> indexDefinitions = createIndexDefinitionHolderForProperty(propertyDotPath.toString(), collection,
 				property);
 
 		if (!indexDefinitions.isEmpty()) {
@@ -733,8 +766,6 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 		 * @author Christoph Strobl
 		 * @author Mark Paluch
 		 */
-		@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
-		@EqualsAndHashCode
 		static class Path {
 
 			private static final Path EMPTY = new Path(Collections.emptyList(), false);
@@ -742,6 +773,11 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 			private final List<PersistentProperty<?>> elements;
 			private final boolean cycle;
 
+			private Path(List<PersistentProperty<?>> elements, boolean cycle) {
+				this.elements = elements;
+				this.cycle = cycle;
+			}
+
 			/**
 			 * @return an empty {@link Path}.
 			 * @since 1.10.8
@@ -843,6 +879,28 @@ public class MongoPersistentEntityIndexResolver implements IndexResolver {
 
 				return builder.toString();
 			}
+
+			@Override
+			public boolean equals(Object o) {
+				if (this == o)
+					return true;
+				if (o == null || getClass() != o.getClass())
+					return false;
+
+				Path that = (Path) o;
+
+				if (this.cycle != that.cycle) {
+					return false;
+				}
+				return ObjectUtils.nullSafeEquals(this.elements, that.elements);
+			}
+
+			@Override
+			public int hashCode() {
+				int result = ObjectUtils.nullSafeHashCode(elements);
+				result = 31 * result + (cycle ? 1 : 0);
+				return result;
+			}
 		}
 	}
 

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

@@ -16,14 +16,8 @@
 package org.springframework.data.mongodb.core.index;
 
 import org.bson.Document;
-
-import lombok.AccessLevel;
-import lombok.NonNull;
-import lombok.RequiredArgsConstructor;
-
 import org.springframework.data.mongodb.core.query.CriteriaDefinition;
-
-import com.mongodb.DBObject;
+import org.springframework.util.Assert;
 
 /**
  * {@link IndexFilter} implementation for usage with plain {@link Document} as well as {@link CriteriaDefinition} filter
@@ -32,10 +26,16 @@ import com.mongodb.DBObject;
  * @author Christoph Strobl
  * @since 1.10
  */
-@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
 public class PartialIndexFilter implements IndexFilter {
 
-	private final @NonNull Object filterExpression;
+	private final Object filterExpression;
+
+	private PartialIndexFilter(Object filterExpression) {
+
+		Assert.notNull(filterExpression, "FilterExpression must not be null!");
+
+		this.filterExpression = filterExpression;
+	}
 
 	/**
 	 * Create new {@link PartialIndexFilter} for given {@link Document filter expression}.

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

@@ -164,7 +164,8 @@ public class BasicMongoPersistentEntity<T> extends BasicPersistentEntity<T, Mong
 	@Override
 	public org.springframework.data.mongodb.core.query.Collation getCollation() {
 
-		Object collationValue = collationExpression != null ? collationExpression.getValue(getEvaluationContext(null), String.class)
+		Object collationValue = collationExpression != null
+				? collationExpression.getValue(getEvaluationContext(null), String.class)
 				: this.collation;
 
 		if (collationValue == null) {

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

@@ -41,7 +41,7 @@ public @interface Document {
 	 * The collection the document representing the entity is supposed to be stored in. If not configured, a default
 	 * collection name will be derived from the type's name. The attribute supports SpEL expressions to dynamically
 	 * calculate the collection to based on a per operation basis.
-	 *
+	 * 
 	 * @return the name of the collection to be used.
 	 */
 	@AliasFor("collection")
@@ -51,7 +51,7 @@ public @interface Document {
 	 * The collection the document representing the entity is supposed to be stored in. If not configured, a default
 	 * collection name will be derived from the type's name. The attribute supports SpEL expressions to dynamically
 	 * calculate the collection to based on a per operation basis.
-	 *
+	 * 
 	 * @return the name of the collection to be used.
 	 */
 	@AliasFor("value")

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

@@ -35,8 +35,9 @@ import org.springframework.lang.Nullable;
  *
  * @author Jon Brisbin
  * @author Oliver Gierke
+ * @author Christoph Strobl
  */
-public class MongoMappingContext extends AbstractMappingContext<BasicMongoPersistentEntity<?>, MongoPersistentProperty>
+public class MongoMappingContext extends AbstractMappingContext<MongoPersistentEntity<?>, MongoPersistentProperty>
 		implements ApplicationContextAware {
 
 	private static final FieldNamingStrategy DEFAULT_NAMING_STRATEGY = PropertyNameFieldNamingStrategy.INSTANCE;
@@ -76,7 +77,7 @@ public class MongoMappingContext extends AbstractMappingContext<BasicMongoPersis
 	 * @see org.springframework.data.mapping.AbstractMappingContext#createPersistentProperty(java.lang.reflect.Field, java.beans.PropertyDescriptor, org.springframework.data.mapping.MutablePersistentEntity, org.springframework.data.mapping.SimpleTypeHolder)
 	 */
 	@Override
-	public MongoPersistentProperty createPersistentProperty(Property property, BasicMongoPersistentEntity<?> owner,
+	public MongoPersistentProperty createPersistentProperty(Property property, MongoPersistentEntity<?> owner,
 			SimpleTypeHolder simpleTypeHolder) {
 		return new CachingMongoPersistentProperty(property, owner, simpleTypeHolder, fieldNamingStrategy);
 	}
@@ -87,7 +88,7 @@ public class MongoMappingContext extends AbstractMappingContext<BasicMongoPersis
 	 */
 	@Override
 	protected <T> BasicMongoPersistentEntity<T> createPersistentEntity(TypeInformation<T> typeInformation) {
-		return new BasicMongoPersistentEntity<T>(typeInformation);
+		return new BasicMongoPersistentEntity<>(typeInformation);
 	}
 
 	/*
@@ -96,7 +97,6 @@ public class MongoMappingContext extends AbstractMappingContext<BasicMongoPersis
 	 */
 	@Override
 	public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
-
 		super.setApplicationContext(applicationContext);
 	}
 
@@ -126,4 +126,17 @@ public class MongoMappingContext extends AbstractMappingContext<BasicMongoPersis
 	public void setAutoIndexCreation(boolean autoCreateIndexes) {
 		this.autoIndexCreation = autoCreateIndexes;
 	}
+
+	@Nullable
+	@Override
+	public MongoPersistentEntity<?> getPersistentEntity(MongoPersistentProperty persistentProperty) {
+
+		MongoPersistentEntity<?> entity = super.getPersistentEntity(persistentProperty);
+
+		if(entity == null || !persistentProperty.isUnwrapped()) {
+			return entity;
+		}
+
+		return new UnwrappedMongoPersistentEntity<>(entity, new UnwrapEntityContext(persistentProperty));
+	}
 }

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

@@ -16,6 +16,7 @@
 package org.springframework.data.mongodb.core.mapping;
 
 import org.springframework.data.mapping.PersistentEntity;
+import org.springframework.data.mapping.model.MutablePersistentEntity;
 import org.springframework.lang.Nullable;
 
 /**
@@ -24,7 +25,7 @@ import org.springframework.lang.Nullable;
  * @author Oliver Gierke
  * @author Christoph Strobl
  */
-public interface MongoPersistentEntity<T> extends PersistentEntity<T, MongoPersistentProperty> {
+public interface MongoPersistentEntity<T> extends MutablePersistentEntity<T, MongoPersistentProperty> {
 
 	/**
 	 * Returns the collection the entity shall be persisted to.
@@ -93,4 +94,12 @@ public interface MongoPersistentEntity<T> extends PersistentEntity<T, MongoPersi
 		return getShardKey().isSharded();
 	}
 
+	/**
+	 * @return {@literal true} if the entity should be unwrapped.
+	 * @since 3.2
+	 */
+	default boolean isUnwrapped() {
+		return false;
+	}
+
 }

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

@@ -123,6 +123,14 @@ public interface MongoPersistentProperty extends PersistentProperty<MongoPersist
 		return field != null ? !FieldType.IMPLICIT.equals(field.targetType()) : false;
 	}
 
+	/**
+	 * @return {@literal true} if the property should be unwrapped.
+	 * @since 3.2
+	 */
+	default boolean isUnwrapped() {
+		return isEntity() && isAnnotationPresent(Unwrapped.class);
+	}
+
 	/**
 	 * Simple {@link Converter} implementation to transform a {@link MongoPersistentProperty} into its field name.
 	 *
@@ -137,7 +145,10 @@ public interface MongoPersistentProperty extends PersistentProperty<MongoPersist
 		 * @see org.springframework.core.convert.converter.Converter#convert(java.lang.Object)
 		 */
 		public String convert(MongoPersistentProperty source) {
-			return source.getFieldName();
+			if (!source.isUnwrapped()) {
+				return source.getFieldName();
+			}
+			return "";
 		}
 	}
 }

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

@@ -0,0 +1,33 @@
+/*
+ * 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.mapping;
+
+/**
+ * @author Christoph Strobl
+ * @since 3.2
+ */
+class UnwrapEntityContext {
+
+	private final MongoPersistentProperty property;
+
+	public UnwrapEntityContext(MongoPersistentProperty property) {
+		this.property = property;
+	}
+
+	public MongoPersistentProperty getProperty() {
+		return property;
+	}
+}

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

@@ -0,0 +1,136 @@
+/*
+ * 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.mapping;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+import javax.annotation.meta.When;
+
+import org.springframework.core.annotation.AliasFor;
+
+/**
+ * The annotation to configure a value object as flattened out in the target document.
+ * <p />
+ * Depending on the {@link OnEmpty value} of {@link #onEmpty()} the property is set to {@literal null} or an empty
+ * instance in the case all unwrapped values are {@literal null} when reading from the result set.
+ *
+ * @author Christoph Strobl
+ * @since 3.2
+ */
+@Documented
+@Retention(value = RetentionPolicy.RUNTIME)
+@Target(value = { ElementType.ANNOTATION_TYPE, ElementType.FIELD, ElementType.METHOD })
+public @interface Unwrapped {
+
+	/**
+	 * Set the load strategy for the unwrapped object if all contained fields yield {@literal null} values.
+	 * <p />
+	 * {@link Nullable @Unwrapped.Nullable} and {@link Empty @Unwrapped.Empty} offer shortcuts for this.
+	 *
+	 * @return never {@link} null.
+	 */
+	OnEmpty onEmpty();
+
+	/**
+	 * @return prefix for columns in the unwrapped value object. An empty {@link String} by default.
+	 */
+	String prefix() default "";
+
+	/**
+	 * Load strategy to be used {@link Unwrapped#onEmpty()}.
+	 *
+	 * @author Christoph Strobl
+	 */
+	enum OnEmpty {
+		USE_NULL, USE_EMPTY
+	}
+
+	/**
+	 * Shortcut for a nullable unwrapped property.
+	 *
+	 * <pre class="code">
+	 * &#64;Unwrapped.Nullable private Address address;
+	 * </pre>
+	 *
+	 * as alternative to the more verbose
+	 *
+	 * <pre class="code">
+	 * &#64;Unwrapped(onEmpty = USE_NULL) &#64;javax.annotation.Nonnull(when = When.MAYBE) private Address address;
+	 * </pre>
+	 *
+	 * @author Christoph Strobl
+	 * @see Unwrapped#onEmpty()
+	 */
+	@Unwrapped(onEmpty = OnEmpty.USE_NULL)
+	@Documented
+	@Retention(RetentionPolicy.RUNTIME)
+	@Target({ ElementType.FIELD, ElementType.METHOD })
+	@javax.annotation.Nonnull(when = When.MAYBE)
+	@interface Nullable {
+
+		/**
+		 * @return prefix for columns in the unwrapped value object. An empty {@link String} by default.
+		 */
+		@AliasFor(annotation = Unwrapped.class, attribute = "prefix")
+		String prefix() default "";
+
+		/**
+		 * @return value for columns in the unwrapped value object. An empty {@link String} by default.
+		 */
+		@AliasFor(annotation = Unwrapped.class, attribute = "prefix")
+		String value() default "";
+	}
+
+	/**
+	 * Shortcut for an empty unwrapped property.
+	 *
+	 * <pre class="code">
+	 * &#64;Unwrapped.Empty private Address address;
+	 * </pre>
+	 *
+	 * as alternative to the more verbose
+	 *
+	 * <pre class="code">
+	 * &#64;Unwrapped(onEmpty = USE_EMPTY) &#64;javax.annotation.Nonnull(when = When.NEVER) private Address address;
+	 * </pre>
+	 *
+	 * @author Christoph Strobl
+	 * @see Unwrapped#onEmpty()
+	 */
+	@Unwrapped(onEmpty = OnEmpty.USE_EMPTY)
+	@Documented
+	@Retention(RetentionPolicy.RUNTIME)
+	@Target({ ElementType.FIELD, ElementType.METHOD })
+	@javax.annotation.Nonnull(when = When.NEVER)
+	@interface Empty {
+
+		/**
+		 * @return prefix for columns in the unwrapped value object. An empty {@link String} by default.
+		 */
+		@AliasFor(annotation = Unwrapped.class, attribute = "prefix")
+		String prefix() default "";
+
+		/**
+		 * @return value for columns in the unwrapped value object. An empty {@link String} by default.
+		 */
+		@AliasFor(annotation = Unwrapped.class, attribute = "prefix")
+		String value() default "";
+	}
+}

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

@@ -0,0 +1,326 @@
+/*
+ * 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.mapping;
+
+import java.lang.annotation.Annotation;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Spliterator;
+import java.util.function.Consumer;
+import java.util.stream.Collectors;
+
+import org.springframework.data.mapping.*;
+import org.springframework.data.mapping.model.PersistentPropertyAccessorFactory;
+import org.springframework.data.mongodb.core.query.Collation;
+import org.springframework.data.spel.EvaluationContextProvider;
+import org.springframework.data.util.Streamable;
+import org.springframework.data.util.TypeInformation;
+import org.springframework.lang.Nullable;
+
+/**
+ * Unwrapped variant of {@link MongoPersistentEntity}.
+ *
+ * @author Christoph Strobl
+ * @since 3.2
+ * @see Unwrapped
+ */
+class UnwrappedMongoPersistentEntity<T> implements MongoPersistentEntity<T> {
+
+	private final UnwrapEntityContext context;
+	private final MongoPersistentEntity<T> delegate;
+
+	public UnwrappedMongoPersistentEntity(MongoPersistentEntity<T> delegate, UnwrapEntityContext context) {
+
+		this.context = context;
+		this.delegate = delegate;
+	}
+
+	@Override
+	public String getCollection() {
+		return delegate.getCollection();
+	}
+
+	@Override
+	public String getLanguage() {
+		return delegate.getLanguage();
+	}
+
+	@Override
+	@Nullable
+	public MongoPersistentProperty getTextScoreProperty() {
+		return delegate.getTextScoreProperty();
+	}
+
+	@Override
+	public boolean hasTextScoreProperty() {
+		return delegate.hasTextScoreProperty();
+	}
+
+	@Override
+	@Nullable
+	public Collation getCollation() {
+		return delegate.getCollation();
+	}
+
+	@Override
+	public boolean hasCollation() {
+		return delegate.hasCollation();
+	}
+
+	@Override
+	public ShardKey getShardKey() {
+		return delegate.getShardKey();
+	}
+
+	@Override
+	public boolean isSharded() {
+		return delegate.isSharded();
+	}
+
+	@Override
+	public String getName() {
+		return delegate.getName();
+	}
+
+	@Override
+	@Nullable
+	public PreferredConstructor<T, MongoPersistentProperty> getPersistenceConstructor() {
+		return delegate.getPersistenceConstructor();
+	}
+
+	@Override
+	public boolean isConstructorArgument(PersistentProperty<?> property) {
+		return delegate.isConstructorArgument(property);
+	}
+
+	@Override
+	public boolean isIdProperty(PersistentProperty<?> property) {
+		return delegate.isIdProperty(property);
+	}
+
+	@Override
+	public boolean isVersionProperty(PersistentProperty<?> property) {
+		return delegate.isVersionProperty(property);
+	}
+
+	@Override
+	@Nullable
+	public MongoPersistentProperty getIdProperty() {
+		return delegate.getIdProperty();
+	}
+
+	@Override
+	public MongoPersistentProperty getRequiredIdProperty() {
+		return delegate.getRequiredIdProperty();
+	}
+
+	@Override
+	@Nullable
+	public MongoPersistentProperty getVersionProperty() {
+		return delegate.getVersionProperty();
+	}
+
+	@Override
+	public MongoPersistentProperty getRequiredVersionProperty() {
+		return delegate.getRequiredVersionProperty();
+	}
+
+	@Override
+	@Nullable
+	public MongoPersistentProperty getPersistentProperty(String name) {
+		return wrap(delegate.getPersistentProperty(name));
+	}
+
+	@Override
+	public MongoPersistentProperty getRequiredPersistentProperty(String name) {
+
+		MongoPersistentProperty persistentProperty = getPersistentProperty(name);
+		if (persistentProperty != null) {
+			return persistentProperty;
+		}
+
+		throw new IllegalStateException(String.format("Required property %s not found for %s!", name, getType()));
+	}
+
+	@Override
+	@Nullable
+	public MongoPersistentProperty getPersistentProperty(Class<? extends Annotation> annotationType) {
+		return wrap(delegate.getPersistentProperty(annotationType));
+	}
+
+	@Override
+	public Iterable<MongoPersistentProperty> getPersistentProperties(Class<? extends Annotation> annotationType) {
+		return Streamable.of(delegate.getPersistentProperties(annotationType)).stream().map(this::wrap)
+				.collect(Collectors.toList());
+	}
+
+	@Override
+	public boolean hasIdProperty() {
+		return delegate.hasIdProperty();
+	}
+
+	@Override
+	public boolean hasVersionProperty() {
+		return delegate.hasVersionProperty();
+	}
+
+	@Override
+	public Class<T> getType() {
+		return delegate.getType();
+	}
+
+	@Override
+	public Alias getTypeAlias() {
+		return delegate.getTypeAlias();
+	}
+
+	@Override
+	public TypeInformation<T> getTypeInformation() {
+		return delegate.getTypeInformation();
+	}
+
+	@Override
+	public void doWithProperties(PropertyHandler<MongoPersistentProperty> handler) {
+
+		delegate.doWithProperties((PropertyHandler<MongoPersistentProperty>) property -> {
+			handler.doWithPersistentProperty(wrap(property));
+		});
+	}
+
+	@Override
+	public void doWithProperties(SimplePropertyHandler handler) {
+
+		delegate.doWithProperties((SimplePropertyHandler) property -> {
+			if (property instanceof MongoPersistentProperty) {
+				handler.doWithPersistentProperty(wrap((MongoPersistentProperty) property));
+			} else {
+				handler.doWithPersistentProperty(property);
+			}
+		});
+	}
+
+	@Override
+	public void doWithAssociations(AssociationHandler<MongoPersistentProperty> handler) {
+		delegate.doWithAssociations(handler);
+	}
+
+	@Override
+	public void doWithAssociations(SimpleAssociationHandler handler) {
+		delegate.doWithAssociations(handler);
+	}
+
+	@Override
+	@Nullable
+	public <A extends Annotation> A findAnnotation(Class<A> annotationType) {
+		return delegate.findAnnotation(annotationType);
+	}
+
+	@Override
+	public <A extends Annotation> A getRequiredAnnotation(Class<A> annotationType) throws IllegalStateException {
+		return delegate.getRequiredAnnotation(annotationType);
+	}
+
+	@Override
+	public <A extends Annotation> boolean isAnnotationPresent(Class<A> annotationType) {
+		return delegate.isAnnotationPresent(annotationType);
+	}
+
+	@Override
+	public <B> PersistentPropertyAccessor<B> getPropertyAccessor(B bean) {
+		return delegate.getPropertyAccessor(bean);
+	}
+
+	@Override
+	public <B> PersistentPropertyPathAccessor<B> getPropertyPathAccessor(B bean) {
+		return delegate.getPropertyPathAccessor(bean);
+	}
+
+	@Override
+	public IdentifierAccessor getIdentifierAccessor(Object bean) {
+		return delegate.getIdentifierAccessor(bean);
+	}
+
+	@Override
+	public boolean isNew(Object bean) {
+		return delegate.isNew(bean);
+	}
+
+	@Override
+	public boolean isImmutable() {
+		return delegate.isImmutable();
+	}
+
+	@Override
+	public boolean requiresPropertyPopulation() {
+		return delegate.requiresPropertyPopulation();
+	}
+
+	@Override
+	public Iterator<MongoPersistentProperty> iterator() {
+
+		List<MongoPersistentProperty> target = new ArrayList<>();
+		delegate.iterator().forEachRemaining(it -> target.add(wrap(it)));
+		return target.iterator();
+	}
+
+	@Override
+	public void forEach(Consumer<? super MongoPersistentProperty> action) {
+		delegate.forEach(it -> action.accept(wrap(it)));
+	}
+
+	@Override
+	public Spliterator<MongoPersistentProperty> spliterator() {
+		return delegate.spliterator();
+	}
+
+	private MongoPersistentProperty wrap(MongoPersistentProperty source) {
+		if (source == null) {
+			return source;
+		}
+		return new UnwrappedMongoPersistentProperty(source, context);
+	}
+
+	@Override
+	public void addPersistentProperty(MongoPersistentProperty property) {
+
+	}
+
+	@Override
+	public void addAssociation(Association<MongoPersistentProperty> association) {
+
+	}
+
+	@Override
+	public void verify() throws MappingException {
+
+	}
+
+	@Override
+	public void setPersistentPropertyAccessorFactory(PersistentPropertyAccessorFactory factory) {
+
+	}
+
+	@Override
+	public void setEvaluationContextProvider(EvaluationContextProvider provider) {
+
+	}
+
+	@Override
+	public boolean isUnwrapped() {
+		return context.getProperty().isUnwrapped();
+	}
+}

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

@@ -0,0 +1,307 @@
+/*
+ * 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.mapping;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+
+import org.springframework.data.mapping.Association;
+import org.springframework.data.mapping.PersistentEntity;
+import org.springframework.data.mapping.PersistentPropertyAccessor;
+import org.springframework.data.util.TypeInformation;
+import org.springframework.lang.Nullable;
+
+/**
+ * Unwrapped variant of {@link MongoPersistentProperty}.
+ *
+ * @author Christoph Strobl
+ * @since 3.2
+ * @see Unwrapped
+ */
+class UnwrappedMongoPersistentProperty implements MongoPersistentProperty {
+
+	private final MongoPersistentProperty delegate;
+	private final UnwrapEntityContext context;
+
+	public UnwrappedMongoPersistentProperty(MongoPersistentProperty delegate, UnwrapEntityContext context) {
+
+		this.delegate = delegate;
+		this.context = context;
+	}
+
+	@Override
+	public String getFieldName() {
+
+		if (!context.getProperty().isUnwrapped()) {
+			return delegate.getFieldName();
+		}
+
+		return context.getProperty().findAnnotation(Unwrapped.class).prefix() + delegate.getFieldName();
+	}
+
+	@Override
+	public Class<?> getFieldType() {
+		return delegate.getFieldType();
+	}
+
+	@Override
+	public int getFieldOrder() {
+		return delegate.getFieldOrder();
+	}
+
+	@Override
+	public boolean isDbReference() {
+		return delegate.isDbReference();
+	}
+
+	@Override
+	public boolean isExplicitIdProperty() {
+		return delegate.isExplicitIdProperty();
+	}
+
+	@Override
+	public boolean isLanguageProperty() {
+		return delegate.isLanguageProperty();
+	}
+
+	@Override
+	public boolean isExplicitLanguageProperty() {
+		return delegate.isExplicitLanguageProperty();
+	}
+
+	@Override
+	public boolean isTextScoreProperty() {
+		return delegate.isTextScoreProperty();
+	}
+
+	@Override
+	@Nullable
+	public DBRef getDBRef() {
+		return delegate.getDBRef();
+	}
+
+	@Override
+	public boolean usePropertyAccess() {
+		return delegate.usePropertyAccess();
+	}
+
+	@Override
+	public boolean hasExplicitWriteTarget() {
+		return delegate.hasExplicitWriteTarget();
+	}
+
+	@Override
+	public PersistentEntity<?, MongoPersistentProperty> getOwner() {
+		return delegate.getOwner();
+	}
+
+	@Override
+	public String getName() {
+		return delegate.getName();
+	}
+
+	@Override
+	public Class<?> getType() {
+		return delegate.getType();
+	}
+
+	@Override
+	public TypeInformation<?> getTypeInformation() {
+		return delegate.getTypeInformation();
+	}
+
+	@Override
+	public Iterable<? extends TypeInformation<?>> getPersistentEntityTypes() {
+		return delegate.getPersistentEntityTypes();
+	}
+
+	@Override
+	@Nullable
+	public Method getGetter() {
+		return delegate.getGetter();
+	}
+
+	@Override
+	public Method getRequiredGetter() {
+		return delegate.getRequiredGetter();
+	}
+
+	@Override
+	@Nullable
+	public Method getSetter() {
+		return delegate.getSetter();
+	}
+
+	@Override
+	public Method getRequiredSetter() {
+		return delegate.getRequiredSetter();
+	}
+
+	@Override
+	@Nullable
+	public Method getWither() {
+		return delegate.getWither();
+	}
+
+	@Override
+	public Method getRequiredWither() {
+		return delegate.getRequiredWither();
+	}
+
+	@Override
+	@Nullable
+	public Field getField() {
+		return delegate.getField();
+	}
+
+	@Override
+	public Field getRequiredField() {
+		return delegate.getRequiredField();
+	}
+
+	@Override
+	@Nullable
+	public String getSpelExpression() {
+		return delegate.getSpelExpression();
+	}
+
+	@Override
+	@Nullable
+	public Association<MongoPersistentProperty> getAssociation() {
+		return delegate.getAssociation();
+	}
+
+	@Override
+	public Association<MongoPersistentProperty> getRequiredAssociation() {
+		return delegate.getRequiredAssociation();
+	}
+
+	@Override
+	public boolean isEntity() {
+		return delegate.isEntity();
+	}
+
+	@Override
+	public boolean isIdProperty() {
+		return delegate.isIdProperty();
+	}
+
+	@Override
+	public boolean isVersionProperty() {
+		return delegate.isVersionProperty();
+	}
+
+	@Override
+	public boolean isCollectionLike() {
+		return delegate.isCollectionLike();
+	}
+
+	@Override
+	public boolean isMap() {
+		return delegate.isMap();
+	}
+
+	@Override
+	public boolean isArray() {
+		return delegate.isArray();
+	}
+
+	@Override
+	public boolean isTransient() {
+		return delegate.isTransient();
+	}
+
+	@Override
+	public boolean isWritable() {
+		return delegate.isWritable();
+	}
+
+	@Override
+	public boolean isImmutable() {
+		return delegate.isImmutable();
+	}
+
+	@Override
+	public boolean isAssociation() {
+		return delegate.isAssociation();
+	}
+
+	@Override
+	public boolean isUnwrapped() {
+		return delegate.isUnwrapped();
+	}
+
+	@Override
+	@Nullable
+	public Class<?> getComponentType() {
+		return delegate.getComponentType();
+	}
+
+	@Override
+	public Class<?> getRawType() {
+		return delegate.getRawType();
+	}
+
+	@Override
+	@Nullable
+	public Class<?> getMapValueType() {
+		return delegate.getMapValueType();
+	}
+
+	@Override
+	public Class<?> getActualType() {
+		return delegate.getActualType();
+	}
+
+	@Override
+	@Nullable
+	public <A extends Annotation> A findAnnotation(Class<A> annotationType) {
+		return delegate.findAnnotation(annotationType);
+	}
+
+	@Override
+	public <A extends Annotation> A getRequiredAnnotation(Class<A> annotationType) throws IllegalStateException {
+		return delegate.getRequiredAnnotation(annotationType);
+	}
+
+	@Override
+	@Nullable
+	public <A extends Annotation> A findPropertyOrOwnerAnnotation(Class<A> annotationType) {
+		return delegate.findPropertyOrOwnerAnnotation(annotationType);
+	}
+
+	@Override
+	public boolean isAnnotationPresent(Class<? extends Annotation> annotationType) {
+		return delegate.isAnnotationPresent(annotationType);
+	}
+
+	@Override
+	public boolean hasActualTypeAnnotation(Class<? extends Annotation> annotationType) {
+		return delegate.hasActualTypeAnnotation(annotationType);
+	}
+
+	@Override
+	@Nullable
+	public Class<?> getAssociationTargetType() {
+		return delegate.getAssociationTargetType();
+	}
+
+	@Override
+	public <T> PersistentPropertyAccessor<T> getAccessorForOwner(T owner) {
+		return delegate.getAccessorForOwner(owner);
+	}
+}

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/mapping/event/MongoMappingEvent.java

@@ -77,7 +77,7 @@ public class MongoMappingEvent<T> extends ApplicationEvent {
 
 	/**
 	 * Allows client code to change the underlying source instance by applying the given {@link Function}.
-	 *
+	 * 
 	 * @param mapper the {@link Function} to apply, will only be applied if the source is not {@literal null}.
 	 * @since 2.1
 	 */

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/mapping/event/ReactiveAuditingEntityCallback.java

@@ -15,13 +15,12 @@
  */
 package org.springframework.data.mongodb.core.mapping.event;
 
-import reactor.core.publisher.Mono;
-
 import org.reactivestreams.Publisher;
+
 import org.springframework.beans.factory.ObjectFactory;
 import org.springframework.core.Ordered;
 import org.springframework.data.auditing.AuditingHandler;
-import org.springframework.data.auditing.IsNewAwareAuditingHandler;
+import org.springframework.data.auditing.ReactiveIsNewAwareAuditingHandler;
 import org.springframework.data.mapping.callback.EntityCallback;
 import org.springframework.data.mapping.context.MappingContext;
 import org.springframework.util.Assert;
@@ -34,7 +33,7 @@ import org.springframework.util.Assert;
  */
 public class ReactiveAuditingEntityCallback implements ReactiveBeforeConvertCallback<Object>, Ordered {
 
-	private final ObjectFactory<IsNewAwareAuditingHandler> auditingHandlerFactory;
+	private final ObjectFactory<ReactiveIsNewAwareAuditingHandler> auditingHandlerFactory;
 
 	/**
 	 * Creates a new {@link ReactiveAuditingEntityCallback} using the given {@link MappingContext} and
@@ -42,7 +41,7 @@ public class ReactiveAuditingEntityCallback implements ReactiveBeforeConvertCall
 	 *
 	 * @param auditingHandlerFactory must not be {@literal null}.
 	 */
-	public ReactiveAuditingEntityCallback(ObjectFactory<IsNewAwareAuditingHandler> auditingHandlerFactory) {
+	public ReactiveAuditingEntityCallback(ObjectFactory<ReactiveIsNewAwareAuditingHandler> auditingHandlerFactory) {
 
 		Assert.notNull(auditingHandlerFactory, "IsNewAwareAuditingHandler must not be null!");
 		this.auditingHandlerFactory = auditingHandlerFactory;
@@ -54,7 +53,7 @@ public class ReactiveAuditingEntityCallback implements ReactiveBeforeConvertCall
 	 */
 	@Override
 	public Publisher<Object> onBeforeConvert(Object entity, String collection) {
-		return Mono.just(auditingHandlerFactory.getObject().markAudited(entity));
+		return auditingHandlerFactory.getObject().markAudited(entity);
 	}
 
 	/*

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

@@ -15,8 +15,6 @@
  */
 package org.springframework.data.mongodb.core.messaging;
 
-import lombok.AllArgsConstructor;
-
 import java.time.Instant;
 import java.util.Arrays;
 import java.util.Collections;
@@ -217,12 +215,17 @@ class ChangeStreamTask extends CursorReadingTask<ChangeStreamDocument<Document>,
 	 *
 	 * @since 2.1
 	 */
-	@AllArgsConstructor
 	static class ChangeStreamEventMessage<T> implements Message<ChangeStreamDocument<Document>, T> {
 
 		private final ChangeStreamEvent<T> delegate;
 		private final MessageProperties messageProperties;
 
+		ChangeStreamEventMessage(ChangeStreamEvent<T> delegate, MessageProperties messageProperties) {
+
+			this.delegate = delegate;
+			this.messageProperties = messageProperties;
+		}
+
 		/*
 		 * (non-Javadoc)
 		 * @see org.springframework.data.mongodb.core.messaging.Message#getRaw()

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

@@ -15,10 +15,6 @@
  */
 package org.springframework.data.mongodb.core.messaging;
 
-import lombok.AccessLevel;
-import lombok.EqualsAndHashCode;
-import lombok.RequiredArgsConstructor;
-
 import java.time.Duration;
 import java.util.LinkedHashMap;
 import java.util.Map;
@@ -34,6 +30,7 @@ import org.springframework.data.mongodb.core.messaging.SubscriptionRequest.Reque
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ErrorHandler;
+import org.springframework.util.ObjectUtils;
 
 /**
  * Simple {@link Executor} based {@link MessageListenerContainer} implementation for running {@link Task tasks} like
@@ -259,7 +256,6 @@ public class DefaultMessageListenerContainer implements MessageListenerContainer
 	 * @author Christoph Strobl
 	 * @since 2.1
 	 */
-	@EqualsAndHashCode
 	static class TaskSubscription implements Subscription {
 
 		private final Task task;
@@ -286,19 +282,39 @@ public class DefaultMessageListenerContainer implements MessageListenerContainer
 		public void cancel() throws DataAccessResourceFailureException {
 			task.cancel();
 		}
+
+		@Override
+		public boolean equals(Object o) {
+			if (this == o)
+				return true;
+			if (o == null || getClass() != o.getClass())
+				return false;
+
+			TaskSubscription that = (TaskSubscription) o;
+
+			return ObjectUtils.nullSafeEquals(this.task, that.task);
+		}
+
+		@Override
+		public int hashCode() {
+			return ObjectUtils.nullSafeHashCode(task);
+		}
 	}
 
 	/**
 	 * @author Christoph Strobl
 	 * @since 2.1
 	 */
-	@RequiredArgsConstructor(access = AccessLevel.PACKAGE)
 	private static class DecoratingLoggingErrorHandler implements ErrorHandler {
 
 		private final Log logger = LogFactory.getLog(DecoratingLoggingErrorHandler.class);
 
 		private final ErrorHandler delegate;
 
+		DecoratingLoggingErrorHandler(ErrorHandler delegate) {
+			this.delegate = delegate;
+		}
+
 		@Override
 		public void handleError(Throwable t) {
 

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

@@ -15,8 +15,6 @@
  */
 package org.springframework.data.mongodb.core.messaging;
 
-import lombok.ToString;
-
 import org.bson.Document;
 import org.springframework.data.mongodb.core.convert.MongoConverter;
 import org.springframework.util.ClassUtils;
@@ -26,7 +24,6 @@ import org.springframework.util.ClassUtils;
  * @author Mark Paluch
  * @since 2.1
  */
-@ToString(of = { "delegate", "targetType" })
 class LazyMappingDelegatingMessage<S, T> implements Message<S, T> {
 
 	private final Message<S, ?> delegate;
@@ -82,4 +79,8 @@ class LazyMappingDelegatingMessage<S, T> implements Message<S, T> {
 	public MessageProperties getProperties() {
 		return delegate.getProperties();
 	}
+
+	public String toString() {
+		return "LazyMappingDelegatingMessage(delegate=" + this.delegate + ", targetType=" + this.targetType + ")";
+	}
 }

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

@@ -15,11 +15,9 @@
  */
 package org.springframework.data.mongodb.core.messaging;
 
-import lombok.EqualsAndHashCode;
-import lombok.ToString;
-
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 
 /**
  * General message abstraction for any type of Event / Message published by MongoDB server to the client. This might be
@@ -65,8 +63,6 @@ public interface Message<S, T> {
 	 * @author Christoph Strobl
 	 * @since 2.1
 	 */
-	@ToString
-	@EqualsAndHashCode
 	class MessageProperties {
 
 		private static final MessageProperties EMPTY = new MessageProperties();
@@ -111,6 +107,34 @@ public interface Message<S, T> {
 			return new MessagePropertiesBuilder();
 		}
 
+		@Override
+		public boolean equals(Object o) {
+			if (this == o)
+				return true;
+			if (o == null || getClass() != o.getClass())
+				return false;
+
+			MessageProperties that = (MessageProperties) o;
+
+			if (!ObjectUtils.nullSafeEquals(this.databaseName, that.databaseName)) {
+				return false;
+			}
+
+			return ObjectUtils.nullSafeEquals(this.collectionName, that.collectionName);
+		}
+
+		@Override
+		public int hashCode() {
+			int result = ObjectUtils.nullSafeHashCode(databaseName);
+			result = 31 * result + ObjectUtils.nullSafeHashCode(collectionName);
+			return result;
+		}
+
+		public String toString() {
+			return "Message.MessageProperties(databaseName=" + this.getDatabaseName() + ", collectionName="
+					+ this.getCollectionName() + ")";
+		}
+
 		/**
 		 * Builder for {@link MessageProperties}.
 		 *

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

@@ -15,11 +15,9 @@
  */
 package org.springframework.data.mongodb.core.messaging;
 
-import lombok.EqualsAndHashCode;
-import lombok.ToString;
-
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
+import org.springframework.util.ObjectUtils;
 
 /**
  * Trivial {@link Message} implementation.
@@ -27,8 +25,6 @@ import org.springframework.util.Assert;
  * @author Christoph Strobl
  * @since 2.1
  */
-@EqualsAndHashCode
-@ToString
 class SimpleMessage<S, T> implements Message<S, T> {
 
 	private @Nullable final S raw;
@@ -75,4 +71,35 @@ class SimpleMessage<S, T> implements Message<S, T> {
 	public MessageProperties getProperties() {
 		return properties;
 	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o)
+			return true;
+		if (o == null || getClass() != o.getClass())
+			return false;
+
+		SimpleMessage<?, ?> that = (SimpleMessage<?, ?>) o;
+
+		if (!ObjectUtils.nullSafeEquals(this.raw, that.raw)) {
+			return false;
+		}
+		if (!ObjectUtils.nullSafeEquals(this.body, that.body)) {
+			return false;
+		}
+		return ObjectUtils.nullSafeEquals(this.properties, that.properties);
+	}
+
+	@Override
+	public int hashCode() {
+		int result = ObjectUtils.nullSafeHashCode(raw);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(body);
+		result = 31 * result + ObjectUtils.nullSafeHashCode(properties);
+		return result;
+	}
+
+	public String toString() {
+		return "SimpleMessage(raw=" + this.getRaw() + ", body=" + this.getBody() + ", properties=" + this.getProperties()
+				+ ")";
+	}
 }

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

@@ -67,6 +67,7 @@ public class BasicUpdate extends Update {
 	}
 
 	@Override
+	@Deprecated
 	public Update pushAll(String key, Object[] values) {
 		Document keyValue = new Document();
 		keyValue.put(key, values);