如何从Hibernate EntityManager正确分离实体

Question

I wanted to test out JPA a little and so I created the following class User :

@Entity
@Table(name="USER")
public class User {

    @Id @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="user")
    private int user_id;

    @Column(name="firstname")
    private String firstname;

    @Column(name="lastname")
    private String lastname;

    protected User() {
    }

    public User(String firstname, String lastname) {
        this.firstname = firstname;
        this.lastname = lastname;
    }
    //getters and setters
}

Now I got the following test-class:

@RunWith(SpringRunner.class)
@DataJpaTest
public class AssignmentTest {
    @Autowired
    private TestEntityManager entityManager;

    @Autowired
    private UserRepository userRepository;

    @Test
    public void whenFindByName_thenReturnUser() {
        //given
        User user = new User("Firstname", "Lastname");
        entityManager.persist(user);
        entityManager.flush();

        //when
        User found = userRepository.findUsersByLastname(user.getLastname()).get(0);

        entityManager.detach(user);
        user.setLastname("Boohoo");

        //then
        assertThat(found.getLastname())
            .isEqualTo("Lastname");
    }
}

Now I'd like the entityManager to stop changing the value of my Entity. I read a few posts that told to use detach , remove or clear - none of it worked out. I still get (on test run):

 org.junit.ComparisonFailure: expected:<"[Lastname]"> but was:<"[Boohoo]">

I tried to see into the statements Hibernate is executing, but I cannot see that hibernate would execute an update -statement.

What did I do wrong on that?

Answer 1

In your example, user and found are pointing to the same object .

First, you call persist on user , meaning that the object that user references becomes a managed entity. You then call:

User found = userRepository.findUsersByLastname(user.getLastname()).get(0);

and, since the User that matches the query criteria is already present in the persistence context, a reference to that (previously persisted) object is returned.

Calling entityManager.detach(user) does detach the entity referenced by user . It's just that found references that very same object at this point.