DATAMONGO-1756 - Fix nested field name resolution for arithmetic aggregation ops.

Original pull request: #491.

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

@@ -1408,7 +1408,7 @@ public class ProjectionOperation implements FieldsExposingAggregationOperation {
 			protected List<Object> getOperationArguments(AggregationOperationContext context) {
 
 				List<Object> result = new ArrayList<Object>(values.size());
-				result.add(context.getReference(getField().getName()).toString());
+				result.add(context.getReference(getField()).toString());
 
 				for (Object element : values) {
 

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

@@ -40,7 +40,7 @@ import com.mongodb.util.JSON;
 
 /**
  * Unit tests for {@link Aggregation}.
- * 
+ *
  * @author Oliver Gierke
  * @author Thomas Darimont
  * @author Christoph Strobl
@@ -564,6 +564,16 @@ public class AggregationUnitTests {
 		assertThat(getAsDBObject(fields, "foosum"), isBsonObject().containing("$first.$cond.else", "no-answer"));
 	}
 
+	@Test // DATAMONGO-1756
+	public void projectOperationShouldRenderNestedFieldNamesCorrectly() {
+
+		DBObject agg = newAggregation(project().and("value1.value").plus("value2.value").as("val")).toDbObject("collection",
+				Aggregation.DEFAULT_CONTEXT);
+
+		assertThat((BasicDBObject) extractPipelineElement(agg, 0, "$project"), is(equalTo(new BasicDBObject("val",
+				new BasicDBObject("$add", new BasicDbListBuilder().add("$value1.value").add("$value2.value").get())))));
+	}
+
 	private DBObject extractPipelineElement(DBObject agg, int index, String operation) {
 
 		List<DBObject> pipeline = (List<DBObject>) agg.get("pipeline");

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

@@ -47,6 +47,7 @@ import org.springframework.data.mongodb.core.convert.QueryMapper;
 import org.springframework.data.mongodb.core.mapping.Document;
 import org.springframework.data.mongodb.core.mapping.MongoMappingContext;
 import org.springframework.data.mongodb.core.query.Criteria;
+import org.springframework.data.mongodb.test.util.BasicDbListBuilder;
 
 import com.mongodb.BasicDBObject;
 import com.mongodb.DBObject;
@@ -54,7 +55,7 @@ import com.mongodb.util.JSON;
 
 /**
  * Unit tests for {@link TypeBasedAggregationOperationContext}.
- * 
+ *
  * @author Oliver Gierke
  * @author Thomas Darimont
  * @author Mark Paluch
@@ -336,6 +337,19 @@ public class TypeBasedAggregationOperationContextUnitTests {
 		assertThat(age, isBsonObject().containing("$ifNull.[1]._class", Age.class.getName()));
 	}
 
+	@Test // DATAMONGO-1756
+	public void projectOperationShouldRenderNestedFieldNamesCorrectlyForTypedAggregation() {
+
+		AggregationOperationContext context = getContext(Wrapper.class);
+
+		DBObject agg = newAggregation(Wrapper.class, project().and("nested1.value1").plus("nested2.value2").as("val"))
+				.toDbObject("collection", context);
+
+		BasicDBObject project = (BasicDBObject) getPipelineElementFromAggregationAt(agg, 0).get("$project");
+		assertThat(project, is(equalTo(new BasicDBObject("val", new BasicDBObject("$add",
+				new BasicDbListBuilder().add("$nested1.value1").add("$field2.nestedValue2").get())))));
+	}
+
 	@Document(collection = "person")
 	public static class FooPerson {
 
@@ -406,4 +420,15 @@ public class TypeBasedAggregationOperationContextUnitTests {
 
 		String name;
 	}
+
+	static class Wrapper {
+
+		Nested nested1;
+		@org.springframework.data.mongodb.core.mapping.Field("field2") Nested nested2;
+	}
+
+	static class Nested {
+		String value1;
+		@org.springframework.data.mongodb.core.mapping.Field("nestedValue2") String value2;
+	}
 }