java – Hibernate Bi-Directional多对多关联创建重复

我上课了,如下所示

@Cache(usage = CacheConcurrencyStrategy.TRANSACTIONAL)
@Entity 
public class A{
     private int id;
     private List<B> listB;

     ...
     @Cache (usage = CacheConcurrencyStrategy.TRANSACTIONAL)
     @ManyToMany(cascade = {CascadeType.PERSIST,CascadeType.MERGE},targetEntity = B.class)
     @JoinTable(name = "A_B",joinColumns = { @JoinColumn(name = "a_id") },inverseJoinColumns = { @JoinColumn(name = "b_id") })
     public List<B> getListB() {
         return listB ;
     }
}

@Cache (usage = CacheConcurrencyStrategy.TRANSACTIONAL)
@Entity
public class B{
     private int id;
     private List<A> listA;

     @ManyToMany(cascade = {CascadeType.PERSIST,targetEntity = A.class)
     @JoinTable(name = "A_B",joinColumns = { @JoinColumn(name = "b_id") },inverseJoinColumns = { @JoinColumn(name = "a_id") })
     public List<a> getListA() {
         return listA ;
     }

     public void addToA(A a) {
         a.getListB().add(this);
     }
}

正如预期的多对多关系一样,我一直在更新双向关系的两个方面.

现在我遇到的问题是,当我尝试添加/更新集合中的项目时,弹出重复的条目.以下是我用来持久保存实体的代码……

b.getA().clear() ;
...
...
b.getListA().add(A) ;
b.addToA(A) ;
em.saveOrUpdate(b) ;

以下是Hibernate从日志中获取的查询.

delete from A_B where b_id=?

insert into A_B (b_id,a_id) values (?,?)
insert into A_B (b_id,?)

delete from A_B where a_id=?

insert into A_B (a_id,b_id) values (?,?)
insert into A_B (a_id,?)

我在哪里错了？
如何摆脱正在插入的重复项？
缓存正在正确刷新,但重复的条目是唯一的问题！