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)
    @JoinTable(name = "ANSWERS_COLLABORATORS", joinColumns = { @JoinColumn(name = "aid") }, inverseJoinColumns = { @JoinColumn(name = "cid") })
    private Set<Collaborator> collaborators = new HashSet<Collaborator>(0);
}

Class Answer has a set of Collaborator, but a Collaborator doesn't keep a set of Answer. What I need to do from Hibernate CriteriaQuery is to find the collaborators for an answer given by id.

I have already done this with Hibernate Criteria (org.hibernate.Criteria) using result transformer, but I'm stuck when it comes to using CriteriaQuery, because I don't have a list of answers to give to the join.

score 33 · Accepted Answer · edited Sep 29 '21 at 14:47

33

It's done, finally...

Here's the code:

public List<Collaborator> getCollaborators(Long answerId) {
  CriteriaBuilder cb = entityManager.getCriteriaBuilder();
  CriteriaQuery<Collaborator> criteriaQuery = cb.createQuery(Collaborator.class);
  
  Root<Answer> answerRoot = criteriaQuery.from(Answer.class);
  SetJoin<Answer, Collaborator> answers = answerRoot.join(Answer_.collaborators);
  criteriaQuery.where(cb.equal(answerRoot.get(Answer_.id), answerId));
  
  return entityManager
    .createQuery(criteriaQuery.select(answers))
    .getResultList();
}

edited Sep 29 '21 at 14:47

Jacob van Lingen

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answered Nov 18 '11 at 08:42

user998692

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Where does the Answer_ come from? – Jukka Hämäläinen Jul 14 '23 at 07:18

Shivan Dragon · Answer 2 · 2011-11-15T12:45:59.403

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

rustem taralov · Answer 3 · 2022-09-23T14:51:36.033

2

Join<Answer , Collaborator> join = root.join("collaborators",JoinType.INNER);

predicates.add(criteriaBuilder.equal(join.get("id"),id));

edited Sep 23 '22 at 14:51

answered Sep 16 '22 at 14:41

rustem taralov

21
2

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As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community Sep 21 '22 at 09:37

score 1 · Answer 4 · answered Nov 16 '21 at 17:00

1

Using criteria Builder :

Join<CLASS_A, CLASS_B> join = root.join(WHAT_UVE_DECLARED_IN_MAPPEDBY, JoinType.INNER);
searchCriteria.add(criteriaBuilder.like(join.get("FIELD_IN_SUBCLASS").as(String.class), "%blabla%"));

answered Nov 16 '21 at 17:00

Saad Joudi

595
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jpa criteria for many to many relationship

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