DATAMONGO-2311 - Add shortcut to project with AggregationExpression to Aggregation.

pom.xml

@@ -5,7 +5,7 @@
 
 	<groupId>org.springframework.data</groupId>
 	<artifactId>spring-data-mongodb-parent</artifactId>
-	<version>2.2.0.BUILD-SNAPSHOT</version>
+	<version>2.2.0.DATAMONGO-2311-SNAPSHOT</version>
 	<packaging>pom</packaging>
 
 	<name>Spring Data MongoDB</name>

spring-data-mongodb-benchmarks/pom.xml

@@ -7,7 +7,7 @@
 	<parent>
 		<groupId>org.springframework.data</groupId>
 		<artifactId>spring-data-mongodb-parent</artifactId>
-		<version>2.2.0.BUILD-SNAPSHOT</version>
+		<version>2.2.0.DATAMONGO-2311-SNAPSHOT</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>2.2.0.BUILD-SNAPSHOT</version>
+		<version>2.2.0.DATAMONGO-2311-SNAPSHOT</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>2.2.0.BUILD-SNAPSHOT</version>
+		<version>2.2.0.DATAMONGO-2311-SNAPSHOT</version>
 		<relativePath>../pom.xml</relativePath>
 	</parent>
 

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

@@ -244,6 +244,29 @@ public static ProjectionOperation project(Fields fields) {
 		return new ProjectionOperation(fields);
 	}
 
+	/**
+	 * Creates a new {@link ProjectionOperation} adding the given {@link AggregationExpression} as projection.
+	 *
+	 * @param expression must not be {@literal null}.
+	 * @return new instance of {@link ProjectionOperation}.
+	 * @throws IllegalArgumentException if the required argument is {@literal null}.
+	 * @since 2.2
+	 */
+	public static ProjectionOperation project(AggregationExpression expression) {
+
+		return new ProjectionOperation(Fields.fields()) {
+
+			@Override
+			public Document toDocument(AggregationOperationContext context) {
+
+				Document target = super.toDocument(context);
+				Document $project = target.get("$project", Document.class);
+				$project.putAll(expression.toDocument(context));
+				return target;
+			}
+		};
+	}
+
 	/**
 	 * Factory method to create a new {@link UnwindOperation} for the field with the given name.
 	 *

spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/aggregation/AggregationTests.java

@@ -1930,6 +1930,13 @@ public void runMatchOperationCriteriaThroughQueryMapperForUntypedAggregation() {
 		assertThat(groupResults.getMappedResults().size()).isEqualTo(4);
 	}
 
+	@Test // DATAMONGO-2311
+	public void projectWithAggregationExpression() {
+
+		assertThat(project(ctx -> new Document("field", 1)).toDocument(Aggregation.DEFAULT_CONTEXT))
+				.isEqualTo(new Document("$project", new Document("field", 1)));
+	}
+
 	private void createUsersWithReferencedPersons() {
 
 		mongoTemplate.dropCollection(User.class);