DATAMONGO-2312 - Add support for array projections.

Original pull request: #770.

Author: christophstrobl

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

@@ -20,6 +20,7 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
+import java.util.stream.Collectors;
 
 import org.bson.Document;
 
@@ -177,6 +178,48 @@ public ProjectionOperation andInclude(Fields fields) {
 		return new ProjectionOperation(this.projections, FieldProjection.from(fields, true));
 	}
 
+	/**
+	 * Includes the current {@link ProjectionOperation} as an array with given name. <br />
+	 * If you want to specify array values directly use {@link #andArrayOf(Object...)}.
+	 *
+	 * @param name the target property name.
+	 * @return new instance of {@link ProjectionOperation}.
+	 * @since 2.2
+	 */
+	public ProjectionOperation asArray(String name) {
+
+		return new ProjectionOperation(Collections.emptyList(),
+				Collections.singletonList(new ArrayProjection(Fields.field(name), (List) this.projections)));
+	}
+
+	/**
+	 * Includes the given values ({@link Field field references}, {@link AggregationExpression expression}, plain values)
+	 * as an array. <br />
+	 * The target property name needs to be set via {@link ArrayProjectionOperationBuilder#as(String)}.
+	 *
+	 * @param values must not be {@literal null}.
+	 * @return new instance of {@link ArrayProjectionOperationBuilder}.
+	 * @throws IllegalArgumentException if the required argument it {@literal null}.
+	 * @since 2.2
+	 */
+	public ArrayProjectionOperationBuilder andArrayOf(Object... values) {
+
+		ArrayProjectionOperationBuilder builder = new ArrayProjectionOperationBuilder(this);
+
+		for (Object value : values) {
+
+			if (value instanceof Field) {
+				builder.and((Field) value);
+			} else if (value instanceof AggregationExpression) {
+				builder.and((AggregationExpression) value);
+			} else {
+				builder.and(value);
+			}
+		}
+
+		return builder;
+	}
+
 	/*
 	 * (non-Javadoc)
 	 * @see org.springframework.data.mongodb.core.aggregation.FieldsExposingAggregationOperation#getFields()
@@ -1743,4 +1786,95 @@ public Document toDocument(AggregationOperationContext context) {
 			return context.getMappedObject(projections, type);
 		}
 	}
+
+	/**
+	 * @author Christoph Strobl
+	 * @since 2.2
+	 */
+	public static class ArrayProjectionOperationBuilder {
+
+		private ProjectionOperation target;
+		private final List<Object> projections;
+
+		public ArrayProjectionOperationBuilder(ProjectionOperation target) {
+
+			this.target = target;
+			this.projections = new ArrayList<>();
+		}
+
+		public ArrayProjectionOperationBuilder and(AggregationExpression expression) {
+
+			this.projections.add(expression);
+			return this;
+		}
+
+		public ArrayProjectionOperationBuilder and(Field field) {
+
+			this.projections.add(field);
+			return this;
+		}
+
+		public ArrayProjectionOperationBuilder and(Object value) {
+
+			this.projections.add(value);
+			return this;
+		}
+
+		/**
+		 * Create the {@link ProjectionOperation} for the array property with given {@literal name}.
+		 *
+		 * @param name The target property name. Must not be {@literal null}.
+		 * @return new instance of {@link ArrayProjectionOperationBuilder}.
+		 */
+		public ProjectionOperation as(String name) {
+
+			return new ProjectionOperation(target.projections,
+					Collections.singletonList(new ArrayProjection(Fields.field(name), this.projections)));
+		}
+	}
+
+	/**
+	 * @author Christoph Strobl
+	 * @since 2.2
+	 */
+	static class ArrayProjection extends Projection {
+
+		private final Field targetField;
+		private final List<Object> projections;
+
+		public ArrayProjection(Field targetField, List<Object> projections) {
+
+			super(targetField);
+			this.targetField = targetField;
+			this.projections = projections;
+		}
+
+		@Override
+		public Document toDocument(AggregationOperationContext context) {
+
+			return new Document(targetField.getName(),
+					projections.stream().map(it -> toArrayEntry(it, context)).collect(Collectors.toList()));
+		}
+
+		private Object toArrayEntry(Object projection, AggregationOperationContext ctx) {
+
+			if (projection instanceof Field) {
+				return ctx.getReference((Field) projection).toString();
+			}
+
+			if (projection instanceof AggregationExpression) {
+				return ((AggregationExpression) projection).toDocument(ctx);
+			}
+
+			if (projection instanceof FieldProjection) {
+				return ctx.getReference(((FieldProjection) projection).getExposedField().getTarget()).toString();
+			}
+
+			if (projection instanceof Projection) {
+				((Projection) projection).toDocument(ctx);
+			}
+
+			return projection;
+		}
+	}
 }

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

@@ -29,6 +29,7 @@
 
 import org.bson.Document;
 import org.junit.Test;
+
 import org.springframework.data.domain.Range;
 import org.springframework.data.domain.Range.Bound;
 import org.springframework.data.mongodb.core.DocumentTestUtils;
@@ -2157,6 +2158,67 @@ public void typeProjectionShouldBeEmptyIfNoPropertiesFound() {
 		assertThat(projectClause).isEmpty();
 	}
 
+	@Test // DATAMONGO-2312
+	public void simpleFieldReferenceAsArray() {
+
+		org.bson.Document doc = Aggregation.newAggregation(project("x", "y", "someField").asArray("myArray"))
+				.toDocument("coll", Aggregation.DEFAULT_CONTEXT);
+
+		assertThat(doc).isEqualTo(Document.parse(
+				"{\"aggregate\":\"coll\", \"pipeline\":[ { $project: { myArray: [ \"$x\", \"$y\", \"$someField\" ] } } ] }"));
+	}
+
+	@Test // DATAMONGO-2312
+	public void mappedFieldReferenceAsArray() {
+
+		MongoMappingContext mappingContext = new MongoMappingContext();
+
+		org.bson.Document doc = Aggregation
+				.newAggregation(BookWithFieldAnnotation.class, project("title", "author").asArray("myArray"))
+				.toDocument("coll", new TypeBasedAggregationOperationContext(BookWithFieldAnnotation.class, mappingContext,
+						new QueryMapper(new MappingMongoConverter(NoOpDbRefResolver.INSTANCE, mappingContext))));
+
+		assertThat(doc).isEqualTo(Document
+				.parse("{\"aggregate\":\"coll\", \"pipeline\":[ { $project: { myArray: [ \"$ti_t_le\", \"$author\" ] } } ] }"));
+	}
+
+	@Test // DATAMONGO-2312
+	public void arrayWithNullValue() {
+
+		Document doc = project() //
+				.andArrayOf(Fields.field("field-1"), null, "value").as("myArray") //
+				.toDocument(Aggregation.DEFAULT_CONTEXT);
+
+		assertThat(doc).isEqualTo(Document.parse("{ $project: { \"myArray\" : [ \"$field-1\", null, \"value\" ] } }"));
+	}
+
+	@Test // DATAMONGO-2312
+	public void nestedArrayField() {
+
+		Document doc = project("_id", "value") //
+				.andArrayOf(Fields.field("field-1"), "plain - string", ArithmeticOperators.valueOf("field-1").sum().and(10))
+				.as("myArray") //
+				.toDocument(Aggregation.DEFAULT_CONTEXT);
+
+		assertThat(doc).isEqualTo(Document.parse(
+				"{ $project: { \"_id\" : 1, \"value\" : 1, \"myArray\" : [ \"$field-1\", \"plain - string\", { \"$sum\" : [\"$field-1\", 10] } ] } } ] }"));
+	}
+
+	@Test // DATAMONGO-2312
+	public void nestedMappedFieldReferenceInArrayField() {
+
+		MongoMappingContext mappingContext = new MongoMappingContext();
+
+		Document doc = project("author") //
+				.andArrayOf(Fields.field("title"), "plain - string", ArithmeticOperators.valueOf("title").sum().and(10))
+				.as("myArray") //
+				.toDocument(new TypeBasedAggregationOperationContext(BookWithFieldAnnotation.class, mappingContext,
+						new QueryMapper(new MappingMongoConverter(NoOpDbRefResolver.INSTANCE, mappingContext))));
+
+		assertThat(doc).isEqualTo(Document.parse(
+				"{ $project: { \"author\" : 1,  \"myArray\" : [ \"$ti_t_le\", \"plain - string\", { \"$sum\" : [\"$ti_t_le\", 10] } ] } } ] }"));
+	}
+
 	private static Document exctractOperation(String field, Document fromProjectClause) {
 		return (Document) fromProjectClause.get(field);
 	}
@@ -2167,6 +2229,13 @@ static class Book {
 		Author author;
 	}
 
+	@Data
+	static class BookWithFieldAnnotation {
+
+		@Field("ti_t_le") String title;
+		Author author;
+	}
+
 	@Data
 	static class BookRenamed {
 		@Field("ti_tl_e") String title;