Question

I have a simple OneToMany association between 2 object Parent & Child as shown below.

Parent Entity

    @Entity
    public class Parent {
     @Id
     @GeneratedValue(strategy = GenerationType.AUTO)
     private Long id;
     private String name;
     @Version
     private Long version;

      @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.EAGER)
      List<Child> children = new ArrayList<Child>();

      ....
    }

Child entity

    @Entity
    public class Child {
      @Id
      @GeneratedValue(strategy = GenerationType.AUTO)
      private Long id;
      private String name;
      @Version
      private Long version;
        ...
    }

Following is my test which loads an existing parent adds a child and calls EntityManager.merge() on the parent.

    @Test
public void testParent(){
    Parent parent = (Parent) dao.loadParent(Parent.class, parentId);

    Child c = new Child();
    c.setName("c");

    parent.getChildren().add(c);

    dao.mergeEntity(parent);

    Assert.assertNotNull(c.getId());
}

The assertion where primary key of the id is tested fails. I see the record being inserted correctly in the database along with the primary key auto assigned.

All my DAO calls are wrapped around transaction with propagation as Required.

Answer 1

EntityManager.merge(..) gets an instance and returns an instance that is managed. And in case of transient instances it returns a new instance (does not modify the original)

So your mergeEntity(..) method should return em.merge(entity)