DATAJPA-931 - Avoid unnecessary merging on save.

Checking if entity is already attached to entity manager before calling merge.

Fixed one test that was relying on the implicit flush triggered by the save.

See also: https://vladmihalcea.com/2016/07/19/jpa-persist-and-merge/

Author: schauder

src/main/java/org/springframework/data/jpa/repository/support/SimpleJpaRepository.java

@@ -66,6 +66,7 @@
  * @author Mark Paluch
  * @author Christoph Strobl
  * @author Stefan Fussenegger
+ * @author Jens Schauder
  * @param <T> the type of the entity to handle
  * @param <ID> the type of the entity's identifier
  */
@@ -487,9 +488,11 @@ public <S extends T> S save(S entity) {
 		if (entityInformation.isNew(entity)) {
 			em.persist(entity);
 			return entity;
-		} else {
+		} else if (!em.contains(entity)) {
 			return em.merge(entity);
 		}
+
+		return entity;
 	}
 
 	/*

src/test/java/org/springframework/data/jpa/domain/support/AuditingEntityListenerTests.java

@@ -41,6 +41,7 @@
  * Integration test for {@link AuditingEntityListener}.
  *
  * @author Oliver Gierke
+ * @author Jens Schauder
  */
 @RunWith(SpringJUnit4ClassRunner.class)
 @ContextConfiguration("classpath:auditing/auditing-entity-listener.xml")
@@ -89,7 +90,9 @@ public void auditsTransitiveEntitiesCorrectly() {
 		role.setName("ADMIN");
 
 		user.addRole(role);
-		repository.save(user);
+
+		repository.saveAndFlush(user);
+
 		role = user.getRoles().iterator().next();
 
 		assertDatesSet(user);

src/test/java/org/springframework/data/jpa/repository/support/SimpleJpaRepositoryUnitTests.java

@@ -44,6 +44,7 @@
  * @author Oliver Gierke
  * @author Thomas Darimont
  * @author Mark Paluch
+ * @author Jens Schauder
  */
 @RunWith(MockitoJUnitRunner.Silent.class)
 public class SimpleJpaRepositoryUnitTests {
@@ -131,4 +132,28 @@ public void shouldPropagateConfiguredEntityGraphToFindOne() throws Exception {
 
 		verify(em).find(User.class, id, singletonMap(EntityGraphType.LOAD.getKey(), (Object) entityGraph));
 	}
+
+	@Test // DATAJPA-931
+	public void mergeGetsCalledWhenDetached() {
+
+		User detachedUser = new User();
+
+		when(em.contains(detachedUser)).thenReturn(false);
+
+		repo.save(detachedUser);
+
+		verify(em).merge(detachedUser);
+	}
+
+	@Test // DATAJPA-931
+	public void mergeGetsNotCalledWhenAttached() {
+
+		User attachedUser = new User();
+
+		when(em.contains(attachedUser)).thenReturn(true);
+
+		repo.save(attachedUser);
+
+		verify(em, never()).merge(attachedUser);
+	}
 }