DATAMONGO-788 - Polishing.

Slightly changed the way the the simple reference rendering for projections is implemented. Introduced an isAliased() method on Field to be able to determine whether the field reference has been renamed explicitly.

Original pull request: spring-projects#90.

Author: odrotbohm

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

@@ -259,6 +259,15 @@ public String getTarget() {
 			return field.getTarget();
 		}
 
+		/*
+		 * (non-Javadoc)
+		 * @see org.springframework.data.mongodb.core.aggregation.Field#isAliased()
+		 */
+		@Override
+		public boolean isAliased() {
+			return field.isAliased();
+		}
+
 		/**
 		 * Returns whether the field can be referred to using the given name.
 		 * 
@@ -349,7 +358,6 @@ public boolean isSynthetic() {
 		public String getRaw() {
 
 			String target = field.getTarget();
-
 			return field.synthetic ? target : String.format("%s.%s", Fields.UNDERSCORE_ID, target);
 		}
 

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

@@ -36,4 +36,11 @@ public interface Field {
 	 * @return must not be {@literal null}.
 	 */
 	String getTarget();
+
+	/**
+	 * Returns whether the Field is aliased, which means it has a name set different from the target.
+	 * 
+	 * @return
+	 */
+	boolean isAliased();
 }

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

@@ -237,6 +237,15 @@ public String getTarget() {
 			return StringUtils.hasText(this.target) ? this.target : this.name;
 		}
 
+		/*
+		 * (non-Javadoc)
+		 * @see org.springframework.data.mongodb.core.aggregation.Field#isAliased()
+		 */
+		@Override
+		public boolean isAliased() {
+			return !getName().equals(getTarget());
+		}
+
 		/* 
 		 * (non-Javadoc)
 		 * @see java.lang.Object#toString()

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

@@ -627,15 +627,8 @@ private Object renderFieldValue(AggregationOperationContext context) {
 
 					// check whether referenced field exists in the context
 					FieldReference reference = context.getReference(field.getTarget());
+					return reference.isSynthetic() && !field.isAliased() ? 1 : reference.toString();
 
-					if (field.getName().equals(field.getTarget()) && reference.isSynthetic()) {
-
-						// render field as included
-						return 1;
-					}
-
-					// render field reference
-					return reference.toString();
 				} else if (Boolean.FALSE.equals(value)) {
 
 					// render field as excluded

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

@@ -117,7 +117,7 @@ public void referencesToGroupIdsShouldBeRenderedAsReferences() {
 		@SuppressWarnings("unchecked")
 		DBObject secondProjection = ((List<DBObject>) agg.get("pipeline")).get(2);
 		DBObject fields = DBObjectTestUtils.getAsDBObject(secondProjection, "$project");
-		assertThat((Integer) fields.get("aCnt"), is(1));
-		assertThat((String) fields.get("a"), is("$_id.a"));
+		assertThat(fields.get("aCnt"), is((Object) 1));
+		assertThat(fields.get("a"), is((Object) "$_id.a"));
 	}
 }

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

@@ -68,7 +68,7 @@ public void alwaysUsesExplicitReference() {
 		DBObject dbObject = operation.toDBObject(Aggregation.DEFAULT_CONTEXT);
 		DBObject projectClause = DBObjectTestUtils.getAsDBObject(dbObject, PROJECT);
 
-		assertThat((Integer) projectClause.get("foo"), is(1));
+		assertThat(projectClause.get("foo"), is((Object) 1));
 		assertThat(projectClause.get("bar"), is((Object) "$foobar"));
 	}