[英]jpa criteria for many to many relationship
我在 Java、Answer 和 Collaborator 中有 2 個 POJO 類,它們是多對多關系。
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
有一組Collaborator
,但Collaborator
不保留一組Answer
。 我需要從 Hibernate CriteriaQuery
中找到合作者以獲取 id 給出的答案。
我已經使用結果轉換器使用 Hibernate Criteria
( org.hibernate.Criteria
) 完成了此操作,但是在使用CriteriaQuery
時我被卡住了,因為我沒有要給連接的答案列表。
它完成了,最后......
這是代碼:
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();
}
使用HQL:
你可以用這個:
Criteria criteria = session.createCriteria(Answer.class);
criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
criteria.createAlias("collaborators", "collaborators");
criteria.add(Restrictions.eq("collaborators.id",desiredCollaboratorId);
獲取與某個協作者關聯的所有答案。
還有這個:
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"));
讓所有協作者與某個答案相關聯。
使用JPA2 Criteria API,您可以執行以下操作:
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
使用標准生成器:
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%"));
Join<Answer, Collaborator> join = root.join("collaborators",JoinType.INNER); predicates.add(criteriaBuilder.equal(partnerEntityCityEntityJoin.get("id"),Long.parseLong(v)));
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