[FIXED] What caused the PersistenceException with the message "detached entity passed to perist"

Issue

I'm using:

• Quarkus with JPA (javax)
• Postgres 11 database

I have:

An Entity

@Entity
@Table(name = "MyEntityTable")
@NamedQuery(name = MyEntity.DOES_EXIST, query = "SELECT x FROM MyEntity x WHERE x.type = :type")
public class MyEntity {

  public static final String DOES_EXIST = "MyEntity.DoesExists";

  @Id
  @SequenceGenerator(name = "myEntitySequence", allocationSize = 1)
  @GeneratedValue(generator = myEntitySequence)
  private long id;

  @Column(name = type)
  private String type;
} 

A repository

@ApplicationScoped
@Transactional(Transactional.TxType.Supports)
public class MyEntityReporitory {

  @Inject
  EntityManager entityManager;

  @Transactional(Transactional.TxType.Required)
  public void persist(final MyEntity entity) {
    entityManager.persist(entiy);
  }

  public boolean doesExist(final String type) {
    final TypedQuery<MyEntity> query = entityManager
      .createNamedQuery(MyEntity.DOES_EXIST, MyEntity.class)
      .setParameter("type", type);
    
    return query.getResultList().size() > 0;
  }
}

A test with two variations

Variation 1

@QuarkusTest
@QuarkusTestResource(DatabaseResource.class) // used to set up a docker container with postgres db
public class MyEntityRepositoryTest {

  private static final MyEntity ENTITY = entity();

  @Inject
  MyEntityRepository subject;

  @Test
  public void testDoesExist() {
    subject.persist(ENTITY);
    final boolean actual = subject.doesExist("type");
    assertTrue(actual);
  }

  @Test
  public void testDoesExist_notMatching() {
    subject.persist(ENTITY);
    final boolean actual = subject.doesExist("another_type");
    assertFalse(actual);
  }

  private static MyEntity entity() {
    final MyEntity result = new MyEntity();
    result.setType("type")
    return result;
  }
}

When I execute this test class (both tests) I'm getting the following Exception on the second time the persist method is called:

javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist com.mypackage.MyEntity
...

Variation 2

I removed the constant ENTITY from the test class, instead I'm calling now the entity() method inside the tests, like:

...
subject.persist(entity());
...

at both places. Now the Exeption is gone and everything is fine.

Question

Can someone explain to me, why this is the case (why variante 2 is working and variante 1 not)?

Solution

https://vladmihalcea.com/jpa-persist-and-merge/

The persist operation must be used only for new entities. From JPA perspective, an entity is new when it has never been associated with a database row, meaning that there is no table record in the database to match the entity in question.

1. testDoesExist executed, ENTITY saved to database and ENTITY.id set to 1
2. testDoesExist_notMatching executed and persist called on ENTITY shows the error beacuse it exists in the database, it has an id assigned

The simplest fix is to call entity() twice, as in you variation 2. But don't forget that the records will exist after a test is run, and might affect your other test cases. You might want to consider cleaning up the data in an @After method or if you intend to use this entity in multiple test cases then put the perist code into a @BeforeClass method.

Answered By - TomasZ.
Answer Checked By - Willingham (JavaFixing Volunteer)