java - hibernate : Update many-tomany intermediary table on Delete

Question

我对 Hibernate 相当陌生，不完全理解应该如何继续更新中间表。

我在两个表之间有多对多关系: session 和出版物

POJO Publication.class:

private List<Conference> conferences;
...
 @ManyToMany(targetEntity = Conference.class, cascade = { CascadeType.PERSIST,
      CascadeType.MERGE })
  @JoinTable(name = "publications_conferences", joinColumns = @JoinColumn(name = "Publications_id"), inverseJoinColumns = @JoinColumn(name = "Conferences_id"))
  public List<Conference> getConferences() {
    return conferences;
  }

  public void setConferences(List<Conference> conferences) {
    this.conferences = conferences;
  }

POJO Conference.class:

private List<Publication> publications;
...
@ManyToMany(targetEntity = Publication.class, mappedBy = "conferences")
  public List<Publication> getPublications() {
    return publications;
  }

  public void setPublications(List<Publication> publications) {
    this.publications = publications;
  }

我的表“conferences”包含重复的记录。我的代码检查两个 session a,b 是否具有相似的标题并删除 a 或 b。现在，我不想删除中间表中的引用(以及记录)，而是想以这种方式更新它:

删除 session “b”之前:

|Publications_id|Conferences_id
-------------------------------
        c       |       a
        d       |       b        

删除 session “d”后:

|Publications_id|Conferences_id
-------------------------------
        c       |       a
        d       |       a        <----- update reference

我尝试了以下代码:

 if (answer == 2) {
            deleteConferenceQ.setParameter("confId", confIdB);

            for (Publication pubB : publicationsB) {

              publicationsA.add(pubB); 
              pubB.getConferences().add(a);
              session.save(pubB);
            }

            int result = deleteConferenceQ.executeUpdate();
            tx.commit();
      }

但是我收到org.hibernate.HibernateException:非法尝试将集合与两个打开的 session 关联。因此我想知道我的做法是否正确。

编辑＃1:我用以下代码替换了以前的代码:

如果(答案==2){

            Iterator<Publication> pubBIter = publicationsB.iterator();
            while (pubBIter.hasNext()) {
              Publication pubB = pubBIter.next();
              pubBIter.remove();
              pubB.getConferences().remove(b);
              b.getPublications().remove(pubB);

              pubB.getConferences().add(a);
              publicationsB.add(pubB);

            }
            session.save(a);
            session.delete(b);
          }

我在 session.save(obj) 上仍然有之前的异常

有人可以帮我吗？谢谢

Answer 1

从 JPA/Hibernate 的角度来看，您甚至不应该考虑连接表。您只需要维护 @ManyToMany 关系的双方并让 Hibernate 管理数据库即可。在您的情况下，它应该归结为从连接表中删除一行并添加一行。您的代码应该如下所示

Publication pub = ...;
Conference confToBeRemoved = ...;
Conference confToBeAdded = ...;

pub.getConferences().remove(confToBeRemoved); // this implies equals() and hashcode() are properly implemented
confToBeRemoved.getPublications().remove(pub); // same here

pub.getConferences().add(confToBeAdded);
confToBeAdded.getPublications().add(pub);

// save all