When having simple parent-child relationship of
*Parent.java*
{code}
@Entity
public class Parent implements Serializable {
@Id
private Integer id;
@OneToMany(fetch = FetchType.EAGER, mappedBy = "parent", orphanRemoval = true, cascade = CascadeType.ALL)
private Set<Child> children = new HashSet<>();
// getters, setters, hashCode, equals omitted for brevity
}
{code}
and *Child.java*:
{code}
@Entity
public class Child implements Serializable {
@Id
@ManyToOne(fetch = FetchType.LAZY, optional = false)
private Parent parent;
@Id
private String value;
// getters, setters, hashCode, equals omitted for brevity
}
{code}
then the following sequence of create-persist-detach-modify-merge:
{code}
EntityManager entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
Parent parent = new Parent();
parent.setId(10);
Child child = new Child();
child.setParent(parent);
child.setValue("old");
parent.getChildren().add(child);
entityManager.persist(parent);
entityManager.flush();
entityManager.detach(parent);
entityManager.getTransaction().commit();
entityManager.close();
// 'parent' is now detached; now let's change it and merge
Child oldChild = parent.getChildren().iterator().next();
Child newChild = new Child();
newChild.setParent(parent);
newChild.setValue("new");
parent.getChildren().add(newChild);
parent.getChildren().remove(oldChild);
entityManager = entityManagerFactory.createEntityManager();
entityManager.getTransaction().begin();
entityManager.merge(parent);
entityManager.getTransaction().commit();
entityManager.close();
{code}
fails with
{code}
Caused by: org.h2.jdbc.JdbcSQLException: NULL not allowed for column "VALUE"; SQL statement:
insert into Child (value, parent_id) values (?, ?) [23502-176]
{code}
See also [this discussion|https://discourse.hibernate.org/t/merge-fails-with-composite-identifier-containing-association/191]. |
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