DATAMONGO-2287 - Add support for $in aggregation pipeline operator.

Original pull request: #760.

Author: sharmashashank342

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

@@ -33,6 +33,7 @@
  *
  * @author Christoph Strobl
  * @author Mark Paluch
+ * @author Shashank Sharma
  * @since 1.0
  */
 public class ArrayOperators {
@@ -1442,6 +1443,7 @@ public Zip zip(Object... arrays) {
 	 * {@link AggregationExpression} for {@code $in}.
 	 *
 	 * @author Christoph Strobl
+	 * @author Shashank Sharma
 	 */
 	public static class In extends AbstractAggregationExpression {
 
@@ -1496,6 +1498,28 @@ public In containsValue(Object value) {
 			};
 		}
 
+		/**
+		 * Support for Aggregation In Search an Element in List of Objects to Filter Start creating {@link In}.
+		 * 
+		 * @author Shashank Sharma
+		 * @param elementList must not be {@literal null}.
+		 * @return
+		 */
+		public static InBuilder arrayOf(final List<Object> elementList) {
+
+			Assert.notNull(elementList, "Elements must not be null!");
+
+			return new InBuilder() {
+
+				@Override
+				public In containsValue(Object value) {
+
+					Assert.notNull(value, "Value must not be null!");
+					return new In(Arrays.asList(value, elementList));
+				}
+			};
+		}
+
 		/**
 		 * @author Christoph Strobl
 		 */

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

@@ -29,6 +29,7 @@
  * Unit tests for {@link ArrayOperators}
  * 
  * @author Christoph Strobl
+ * @author Shashank Sharma
  * @currentRead Royal Assassin - Robin Hobb
  */
 public class ArrayOperatorsUnitTests {
@@ -61,4 +62,12 @@ public void toArrayWithArgumentList() {
 		assertThat(ArrayToObject.arrayToObject(source).toDocument(Aggregation.DEFAULT_CONTEXT))
 				.isEqualTo(Document.parse("{ $arrayToObject: [ [ \"king\", \"shrewd\"], [ \"prince\", \"verity\" ] ] } "));
 	}
+
+	@Test // DATAMONGO-2287
+	public void inArrayAggregationWithArgumentList() {
+
+		assertThat(ArrayOperators.In.arrayOf(Arrays.asList("Shashank", "Sharma")).containsValue("$userName")
+				.toDocument(Aggregation.DEFAULT_CONTEXT))
+						.isEqualTo(Document.parse("{ \"$in\" : [\"$userName\", [\"Shashank\", \"Sharma\"]] }"));
+	}
 }