JPA / Hibernate - ConstraintViolationException by removing an element

Question

Hello!

I have a JPA/Hibernate problem with a n:m relation (Project <-> Person) with a join table. The Project is the mapping owner and has a (cascade = CascadeType.ALL).

Now I want to remove a project which is associated with a Person, so there is an entry in the Project_Person join table, but I get a

org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update

because the entry of the Project_Person table is not deleted before the project should be removed.

Here is the removeProject method:

public void removeProject(int projectId){
    SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
    Session sess = sessionFactory.getCurrentSession();
    Transaction tx = sess.beginTransaction();
    try {
        Project p = (Project)sess.createQuery("from Project where id = "+projectId).list().get(0);
        sess.delete(p);
        tx.commit();
    }
    catch (IndexOutOfBoundsException ex) {System.out.println("exception: "+ex);}
}

All is inside the transaction, so there is not a problem. But why does the sess.selete(p) not automatically remove the entry from the join table?

Does anyone know? Best Regards Tim.

Update:

Person.java:

@ManyToMany(mappedBy="persons")
private Set<Project> projects = new HashSet<Project>();

Project.java:

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "Project_Person",
    joinColumns = {@JoinColumn(name="project_id", referencedColumnName="id")},
    inverseJoinColumns = {@JoinColumn(name="person_id", referencedColumnName="id")}
)
private Set<Person> persons = new HashSet<Person>();

Answer 1

I can answer my question: I need to set the persons to null:

p.setPersons(null);

and everything is okay.