DATAMONGO-1586 - Consider field name in TypeBasedAggregationOperationContext.getReferenceFor(…).

We now consider the provided field name (alias) in mapped fields with which it is exposed. The field name applies to the exposed field after property path resolution in TypeBasedAggregationOperationContext. Previously, the field reference used the property name which caused fields to be considered non-aliased, so aggregation projection operations dropped the alias and exposed the field with its leaf property name.

Original Pull Request: #434

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2013 the original author or authors.
+ * Copyright 2013-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,6 +35,7 @@ import com.mongodb.DBObject;
  * property references into document field names.
  * 
  * @author Oliver Gierke
+ * @author Mark Paluch
  * @since 1.3
  */
 public class TypeBasedAggregationOperationContext implements AggregationOperationContext {
@@ -96,7 +97,7 @@ public class TypeBasedAggregationOperationContext implements AggregationOperatio
 
 		PersistentPropertyPath<MongoPersistentProperty> propertyPath = mappingContext.getPersistentPropertyPath(
 				field.getTarget(), type);
-		Field mappedField = field(propertyPath.getLeafProperty().getName(),
+		Field mappedField = field(field.getName(),
 				propertyPath.toDotPath(MongoPersistentProperty.PropertyToFieldNameConverter.INSTANCE));
 
 		return new DirectFieldReference(new ExposedField(mappedField, true));

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

@@ -17,6 +17,7 @@ package org.springframework.data.mongodb.core.aggregation;
 
 import static org.hamcrest.CoreMatchers.*;
 import static org.junit.Assert.*;
+import static org.springframework.data.mongodb.core.DBObjectTestUtils.*;
 import static org.springframework.data.mongodb.core.aggregation.Aggregation.*;
 import static org.springframework.data.mongodb.core.aggregation.Fields.*;
 import static org.springframework.data.mongodb.test.util.IsBsonObject.*;
@@ -193,6 +194,27 @@ public class TypeBasedAggregationOperationContextUnitTests {
 		assertThat(definition.get("counter"), is(equalTo((Object) 1)));
 	}
 
+	/**
+	 * @see DATAMONGO-1586
+	 */
+	@Test
+	public void rendersFieldAliasingProjectionCorrectly() {
+
+		AggregationOperationContext context = getContext(FooPerson.class);
+		TypedAggregation<FooPerson> agg = newAggregation(FooPerson.class,
+				project() //
+						.and("name").as("person_name") //
+						.and("age.value").as("age"));
+
+		DBObject dbo = agg.toDbObject("person", context);
+
+		DBObject projection = getPipelineElementFromAggregationAt(dbo, 0);
+		assertThat(getAsDBObject(projection, "$project"),
+				isBsonObject() //
+						.containing("person_name", "$name") //
+						.containing("age", "$age.value"));
+	}
+
 	/**
 	 * @see DATAMONGO-1133
 	 */