Avoid duplicate context nesting to properly convert nested projections.

Closes: #4609
Original pull request: #4616

Author: christophstrobl

Diff for: spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/convert/MappingMongoConverter.java

@@ -595,7 +595,6 @@ private void readProperties(ConversionContext context, MongoPersistentEntity<?>
 			}
 
 			ConversionContext propertyContext = context.forProperty(prop);
-			MongoDbPropertyValueProvider valueProviderToUse = valueProvider.withContext(propertyContext);
 
 			if (prop.isAssociation()) {
 
@@ -623,7 +622,7 @@ private void readProperties(ConversionContext context, MongoPersistentEntity<?>
 				continue;
 			}
 
-			accessor.setProperty(prop, valueProviderToUse.getPropertyValue(prop));
+			accessor.setProperty(prop, valueProvider.getPropertyValue(prop));
 		}
 	}
 
@@ -2436,6 +2435,8 @@ class ProjectingConversionContext extends DefaultConversionContext {
 			this.returnedTypeDescriptor = projection;
 		}
 
+
+
 		@Override
 		public ConversionContext forProperty(String name) {
 

Diff for: spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/MongoTemplateTests.java

@@ -2554,6 +2554,30 @@ public void findAndReplaceShouldProjectReturnedObjectCorrectly() {
 		assertThat(projection.getName()).isEqualTo("Walter");
 	}
 
+	@Test // GH-4609
+	public void shouldReadNestedProjection() {
+
+		MyPerson walter = new MyPerson("Walter");
+		walter.address = new Address("spring", "data");
+		template.save(walter);
+
+		PersonPWA result = template.query(MyPerson.class)
+				.as(PersonPWA.class)
+				.matching(where("id").is(walter.id))
+				.firstValue();
+
+		assertThat(result.getAddress().getCity()).isEqualTo("data");
+	}
+
+	interface PersonPWA {
+		String getName();
+		AdressProjection getAddress();
+	}
+
+	interface AdressProjection {
+		String getCity();
+	}
+
 	@Test // GH-4300
 	public void findAndReplaceShouldAllowNativeDomainTypesAndReturnAProjection() {
 

Diff for: spring-data-mongodb/src/test/java/org/springframework/data/mongodb/core/convert/MappingMongoConverterUnitTests.java

@@ -2851,6 +2851,44 @@ void projectShouldReadNestedProjection() {
 		assertThat(person.getAddresses()).extracting(AddressProjection::getStreet).hasSize(1).containsOnly("hwy");
 	}
 
+	@Test // GH-4609
+	void projectShouldReadNestedInterfaceProjection() {
+
+		org.bson.Document source = new org.bson.Document("foo", "spring").append("address",
+				new org.bson.Document("s", "data").append("city", "mongodb"));
+
+		EntityProjectionIntrospector introspector = EntityProjectionIntrospector.create(converter.getProjectionFactory(),
+				EntityProjectionIntrospector.ProjectionPredicate.typeHierarchy()
+						.and((target, underlyingType) -> !converter.conversions.isSimpleType(target)),
+				mappingContext);
+
+		EntityProjection<WithNestedInterfaceProjection, Person> projection = introspector.introspect(WithNestedInterfaceProjection.class,
+				Person.class);
+		WithNestedInterfaceProjection person = converter.project(projection, source);
+
+		assertThat(person.getFirstname()).isEqualTo("spring");
+		assertThat(person.getAddress().getStreet()).isEqualTo("data");
+	}
+
+	@Test // GH-4609
+	void projectShouldReadNestedDtoProjection() {
+
+		org.bson.Document source = new org.bson.Document("foo", "spring").append("address",
+				new org.bson.Document("s", "data").append("city", "mongodb"));
+
+		EntityProjectionIntrospector introspector = EntityProjectionIntrospector.create(converter.getProjectionFactory(),
+				EntityProjectionIntrospector.ProjectionPredicate.typeHierarchy()
+						.and((target, underlyingType) -> !converter.conversions.isSimpleType(target)),
+				mappingContext);
+
+		EntityProjection<WithNestedDtoProjection, Person> projection = introspector.introspect(WithNestedDtoProjection.class,
+				Person.class);
+		WithNestedDtoProjection person = converter.project(projection, source);
+
+		assertThat(person.getFirstname()).isEqualTo("spring");
+		assertThat(person.getAddress().getStreet()).isEqualTo("data");
+	}
+
 	@Test // GH-2860
 	void projectShouldReadProjectionWithNestedEntity() {
 
@@ -3206,6 +3244,7 @@ static class Person implements Contact {
 		String lastname;
 
 		Set<Address> addresses;
+		Address address;
 
 		Person() {
 
@@ -3248,6 +3287,16 @@ interface WithNestedProjection {
 		Set<AddressProjection> getAddresses();
 	}
 
+	interface WithNestedInterfaceProjection {
+		String getFirstname();
+		AddressProjection getAddress();
+	}
+
+	interface WithNestedDtoProjection {
+		String getFirstname();
+		AddressDto getAddress();
+	}
+
 	interface ProjectionWithNestedEntity {
 
 		Set<Address> getAddresses();
@@ -3258,6 +3307,19 @@ interface AddressProjection {
 		String getStreet();
 	}
 
+	class AddressDto {
+
+		String street;
+
+		public String getStreet() {
+			return street;
+		}
+
+		public void setStreet(String street) {
+			this.street = street;
+		}
+	}
+
 	static class PersonDto {
 
 		LocalDate birthDate;