DATAMONGO-2513 - Fix Eq aggregation operator comparing collection values.

Original pull request: #855.

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

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.core.aggregation;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.Collection;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
@@ -100,14 +101,14 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 		return value;
 	}
 
-	protected List<Object> append(Object value) {
+	protected List<Object> append(Object value, Expand expandList) {
 
 		if (this.value instanceof List) {
 
 			List<Object> clone = new ArrayList<Object>((List) this.value);
 
-			if (value instanceof List) {
-				clone.addAll((List) value);
+			if (value instanceof Collection && Expand.EXPAND_VALUES.equals(expandList)) {
+				clone.addAll((Collection<?>) value);
 			} else {
 				clone.add(value);
 			}
@@ -117,6 +118,17 @@ abstract class AbstractAggregationExpression implements AggregationExpression {
 		return Arrays.asList(this.value, value);
 	}
 
+	/**
+	 * Expand a nested list of values to single entries or keep the list.
+	 */
+	protected enum Expand {
+		EXPAND_VALUES, KEEP_SOURCE
+	}
+
+	protected List<Object> append(Object value) {
+		return append(value, Expand.EXPAND_VALUES);
+	}
+
 	@SuppressWarnings("unchecked")
 	protected java.util.Map<String, Object> append(String key, Object value) {
 

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

@@ -411,7 +411,7 @@ public class ComparisonOperators {
 		public Cmp compareToValue(Object value) {
 
 			Assert.notNull(value, "Value must not be null!");
-			return new Cmp(append(value));
+			return new Cmp(append(value, Expand.KEEP_SOURCE));
 		}
 	}
 
@@ -488,7 +488,7 @@ public class ComparisonOperators {
 		public Eq equalToValue(Object value) {
 
 			Assert.notNull(value, "Value must not be null!");
-			return new Eq(append(value));
+			return new Eq(append(value, Expand.KEEP_SOURCE));
 		}
 	}
 
@@ -873,7 +873,7 @@ public class ComparisonOperators {
 		public Ne notEqualToValue(Object value) {
 
 			Assert.notNull(value, "Value must not be null!");
-			return new Ne(append(value));
+			return new Ne(append(value, Expand.KEEP_SOURCE));
 		}
 	}
 }

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

@@ -1499,6 +1499,15 @@ public class ProjectionOperationUnitTests {
 		assertThat(agg).isEqualTo(Document.parse("{ $project: { eq250: { $eq: [\"$qty\", 250]} } }"));
 	}
 
+	@Test // DATAMONGO-2513
+	public void shouldRenderEqAggregationExpressionWithListComparison() {
+
+		Document agg = project().and(ComparisonOperators.valueOf("qty").equalToValue(Arrays.asList(250))).as("eq250")
+				.toDocument(Aggregation.DEFAULT_CONTEXT);
+
+		assertThat(agg).isEqualTo(Document.parse("{ $project: { eq250: { $eq: [\"$qty\", [250]]} } }"));
+	}
+
 	@Test // DATAMONGO-1536
 	public void shouldRenderGtAggregationExpression() {