jpa多对多关系的标准 [英] jpa criteria for many to many relationship

问题描述

  class答案在Java，Answer和Collaborator中我有2个POJO类，在多对多的关系中。 {
 @ManyToMany（cascade = CascadeType.ALL）
 @JoinTable（name =ANSWERS_COLLABORATORS，joinColumns = {@JoinColumn（name =aid）}，inverseJoinColumns = {@JoinColumn（name = cid）}）
 private Set< Collaborator>协作者=新的HashSet<协作者>（0）; 
 
  

Class Answer has一组协作者，但协作者不保留一组 Answer 。
我需要从Hibernate做些什么 CriteriaQuery 是为id找到的答案寻找协作者。

我已经用Hibernate Criteria （ org.hibernate.Criteria ）使用结果转换器完成了这项工作，但是I' m在使用 CriteriaQuery 时陷入困境，因为我没有给出连接的答案列表。

完成后，终于...

以下是代码：

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

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.

解决方案

It's done, finally...

Here's the code:

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();

    }

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