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

Original pull request: spring-projects#491.

Author: christophstrobl

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

@@ -1407,7 +1407,7 @@ public Document toDocument(AggregationOperationContext context) {
 			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

@@ -559,6 +559,16 @@ public void groupOperationShouldAllowUsageOfDerivedSpELAggregationExpression() {
 		assertThat(getAsDocument(fields, "foosum"), isBsonObject().containing("$first.$cond.else", "no-answer"));
 	}
 
+	@Test // DATAMONGO-1756
+	public void projectOperationShouldRenderNestedFieldNamesCorrectly() {
+
+		Document agg = newAggregation(project().and("value1.value").plus("value2.value").as("val")).toDocument("collection",
+				Aggregation.DEFAULT_CONTEXT);
+
+		assertThat(extractPipelineElement(agg, 0, "$project"),
+				is(equalTo(new Document("val", new Document("$add", Arrays.asList("$value1.value", "$value2.value"))))));
+	}
+
 	private Document extractPipelineElement(Document agg, int index, String operation) {
 
 		List<Document> pipeline = (List<Document>) agg.get("pipeline");

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

@@ -338,6 +338,18 @@ public void rendersAggregationIfNullInTypedAggregationContextCorrectly() {
 		assertThat(age, isBsonObject().containing("$ifNull.[1]._class", Age.class.getName()));
 	}
 
+	@Test // DATAMONGO-1756
+	public void projectOperationShouldRenderNestedFieldNamesCorrectlyForTypedAggregation() {
+
+		AggregationOperationContext context = getContext(Wrapper.class);
+
+		Document agg = newAggregation(Wrapper.class, project().and("nested1.value1").plus("nested2.value2").as("val"))
+				.toDocument("collection", context);
+
+		assertThat(getPipelineElementFromAggregationAt(agg, 0).get("$project"), is(
+				equalTo(new Document("val", new Document("$add", Arrays.asList("$nested1.value1", "$field2.nestedValue2"))))));
+	}
+
 	@org.springframework.data.mongodb.core.mapping.Document(collection = "person")
 	public static class FooPerson {
 
@@ -408,4 +420,15 @@ static class Bar {
 
 		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;
+	}
 }