休眠：更新 many-tomany 中介 table 删除

Question

我是 Hibernate 的新手，不完全理解我应该如何继续更新中介 table。

我在两个 table 之间有一个 ManyToMany 关系：会议和出版物

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

删除会议“b”之前：

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

删除会议“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();
      }

但是我收到了 org.hibernate.HibernateException: Illegal attempt to associate a collection with two open sessions。所以我想知道我做的是否正确。

编辑 #1: 我用 :

替换了之前的代码

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)

时仍然有之前的异常

有人可以帮我吗？谢谢

Answer 1

从 JPA/Hibernate 的角度来看，您甚至不应该考虑联接 table。您只需要维护 @ManyToMany 关系的双方并让 Hibernate 管理数据库。在您的情况下，应该归结为删除一行并从连接 table 添加一行。您的代码应如下所示

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

休眠：更新 many-tomany 中介 table 删除

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