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JPA (Hibernate) - Session/Transaction and lazy loading

Answer 1

+2 A:

What you really want to do is push all of the Person removal code down into the PersonDao's remove() method. Inside that method, you want to do the following:

begin transaction
Find Person instance by the id
Get its Project set and remove it from all of them
Remove the Person instance itself
commit transaction

In JPA, you shouldn't need to do anything more than that, however I believe in straight Hibernate you may need to saveOrUpdate then changes made to each Project as well as remove the Person.

So your code might look something like this:

public void removePerson(int personId) {
  SessionFactory sessionFactory = HibernateUtil.getSessionFactory();
  Session sess = sessionFactory.getCurrentSession();
  Transaction tx = sess.beginTransaction();

  try {
    Person person = (Person)sess.createQuery("from Person where id = "+personId).list().get(0);
    Set<Project> projects = person.getProjects();
    for (Project project : projects) {
      if (project.getPersons().contains(person)) {
        project.getPersons().remove(person);
        sess.saveOrUpdate(project);
      }
    }

    sess.delete(person);
    tx.commit();
  }  catch (Exception e) {
     System.err.println("Failed deleting Person: "+e.getMessage());
  }
}

(Note: this is roughly closer to pseudo code and has not been tested inside an actual IDE)

Ophidian 2010-10-14 13:33:17

I added _person.getProjects();_ before _tx.commit();_ but unfortunately same result.

Tim 2010-10-14 13:45:10

My bad, I should have read the question much more closely. I've updated my answer.

Ophidian 2010-10-14 14:13:26

I used your code, but I get the same error in this line: for (Project project : projects) { - lazy initialization exception

Tim 2010-10-14 14:22:12

I'm an idiot, the findPersonById has its own session so it can't be re-used in my removePerson method. Try it with the query directly in the removePerson method.

Ophidian 2010-10-14 14:52:09

Thanks a lot, now it works! My JUnit tests are green :-) So I should do all such performances into the transaction of the Dao implementation? Because I have another problem like this, so I will do this in this kind.

Tim 2010-10-14 14:59:23

Yes, all the cleanup for removing an object should really be carried out within the Dao.

Ophidian 2010-10-14 15:10:23

Answer 2

+1 A:

You have two options here really. The first one is to perform this in your service/DAO implementation.

projectDao.removePersonFrom(Person personToRemove, Project projectToRemoveFrom);

personDao.removeProjectFrom(Project projectToRemove, Person personToRemoveFrom);

I usually have a Model class associated with a view and sometimes I make certain methods in them transactional (I use Spring) to do this kind of stuff.

--edit--

Inside the daos you create your session/transaction and then you can do the code that fails. The code you have posted should work fine.

willcodejavaforfood 2010-10-14 13:53:07

And what should be the vontent of the methode removePersonFrom? Because there is one person and only one project. But I do not know the projects which the person is associated to. I also have Spring implemented for Dependency Injection.

Tim 2010-10-14 14:02:03

I meant I use it to declare transaction boundries

willcodejavaforfood 2010-10-14 14:35:46

You are also right, I have to put all the stuff from the ServiceImpl to the DaoImpl inside the transaction.

Tim 2010-10-14 15:00:11

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