DATAMONGO-1569 - Add partialFilter to Indexed annotation.

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

@@ -46,6 +46,7 @@ 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.spel.EvaluationContextProvider;
 import org.springframework.data.util.TypeInformation;
 import org.springframework.expression.EvaluationContext;
@@ -474,9 +475,25 @@ 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}.

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/index/MongoPersistentEntityIndexResolverUnitTests.java

@@ -271,6 +271,16 @@ public class MongoPersistentEntityIndexResolverUnitTests {
 			assertThat(indexDefinitions.get(0).getIndexOptions()).containsEntry("name", "my1st");
 		}
 
+		@Test // DATAMONGO-1569
+		public void resolvesPartialFilter() {
+
+			List<IndexDefinitionHolder> indexDefinitions = prepareMappingContextAndResolveIndexForType(
+					WithPartialFilter.class);
+
+			assertThat(indexDefinitions.get(0).getIndexOptions()).containsEntry("partialFilterExpression",
+					org.bson.Document.parse("{'value': {'$exists': true}}"));
+		}
+
 		@Document("Zero")
 		static class IndexOnLevelZero {
 			@Indexed String indexedProperty;
@@ -395,6 +405,11 @@ public class MongoPersistentEntityIndexResolverUnitTests {
 		static class WithIndexNameAsExpression {
 			@Indexed(name = "#{'my' + 1 + 'st'}") String spelIndexName;
 		}
+
+		@Document
+		class WithPartialFilter {
+			@Indexed(partialFilter = "{'value': {'$exists': true}}") String withPartialFilter;
+		}
 	}
 
 	@Target({ ElementType.FIELD })