jpa criteria for many to many relationship

Question

I have 2 POJO classes in Java, Answer and Collaborator, in a many-to-many relationship.

class Answer {
    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTa         


        

Answer 1

Using HQL:

You can use this:

Criteria criteria = session.createCriteria(Answer.class);
criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
criteria.createAlias("collaborators", "collaborators");
criteria.add(Restrictions.eq("collaborators.id",desiredCollaboratorId);

to get all the Answers associated to a certain Collaborator.

And this:

Criteria criteria = session.createCriteria(Answer.class);
criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
criteria.setFetchMode("collaborators", FetchMode.JOIN)
criteria.add(Restrictions.idEq(desiredAnswerId));
dsrTrackingCriteria.setProjection(Projections.property("collaborators"));

To get all Collaborators associated to a certain Answer.

Using JPA2 Criteria API you can do something like:

CriteriaBuilder cb = em.getCriteriaBuilder(); //creted from EntityManager instance

CriteriaQuery cq = cb.createQuery(Collaborator.class);
Root rootAnswer = cq.from(Answer.class);
Join joinAnswerCollaborator = rootAnswer.join("collaborators"); //(or rootAnswer.join(Answer_.collaborators); if you've created the metamodel with JPA2