许多关系的jpa标准

Question

我在Java,Answer和Collaborator中有2个POJO类,处于多对多关系中.

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);
} 

类Answer有一套Collaborator,但是Collaborator不保留一套Answer.我需要从Hibernate做的CriteriaQuery是找到id给出的答案的协作者.

我已经使用结果转换器在Hibernate Criteria(org.hibernate.Criteria)中完成了这个,但是在使用时我遇到了困难CriteriaQuery,因为我没有给出连接的答案列表.

Answer 1

它完成了,最后......

这是代码:

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

    }

Answer 2

使用HQL:

你可以用这个:

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

获取与某个协作者关联的所有答案.

还有这个:

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"));

让所有协作者与某个答案相关联.

使用JPA2 Criteria API,您可以执行以下操作:

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