Add support for DTO projections on derived query methods.

In case a derived query uses a DTO, we now create a select clause that uses a constructor expression for the DTO type. This wasn't supported before and expexted either an interface-based projection or an explicit query using a constructor expression.

Fixes #2363.

Author: odrotbohm

src/main/java/org/springframework/data/jpa/repository/query/JpaQueryCreator.java

@@ -176,7 +176,12 @@ protected CriteriaQuery<? extends Object> complete(@Nullable Predicate predicate
 				selections.add(toExpressionRecursively(root, path, true).alias(property));
 			}
 
-			query = query.multiselect(selections);
+			Class<?> typeToRead = returnedType.getTypeToRead();
+
+			query = typeToRead.isInterface()
+					? query.multiselect(selections)
+					: query.select((Selection) builder.construct(typeToRead,
+							selections.toArray(new Selection[0])));
 
 		} else if (tree.isExistsProjection()) {
 

src/test/java/org/springframework/data/jpa/repository/UserRepositoryTests.java

@@ -2599,6 +2599,14 @@ void findByElementCollectionInAttributeIgnoreCaseWithNulls() {
 		assertThat(result).containsOnly(firstUser);
 	}
 
+	@Test // #2363
+	void readsDtoProjections() {
+
+		flushTestUsers();
+
+		assertThat(repository.findAllDtoProjectedBy()).hasSize(4);
+	}
+
 	private Page<User> executeSpecWithSort(Sort sort) {
 
 		flushTestUsers();

src/test/java/org/springframework/data/jpa/repository/sample/UserRepository.java

@@ -611,6 +611,9 @@ Page<User> findAllOrderedBySpecialNameMultipleParams(@Param("name") String name,
 	// DATAJPA-1303
 	Page<User> findByAttributesIgnoreCaseIn(Pageable pageable, String... attributes);
 
+	// #2363
+	List<NameOnlyDto> findAllDtoProjectedBy();
+
 	interface RolesAndFirstname {
 
 		String getFirstname();