我的A实体<-&燃气轮机;B实体关系通过R实体完成。然而,R有额外的信息阻止使用@ManyToMany:

id  | id_a | id_b | previous | ordering_index
----------------------------------------------
 1  |  1   |  10  |    2     |       1
 2  |  1   |  15  |   null   |       0
 3  |  1   |  18  |    1     |       2

JPA实体

@Entity
// ...
public class A{
    // ...
    @OneToMany(mappedBy="master", cascade = Cascade.ALL, orphanRemoval = true)
    @OrderBy("ordering")
    private List<R> bList;
    // ....
}

@Entity
// ...
public class B{
    // ...
    @OneToMany(mappedBy="slave", cascade = Cascade.REMOVE)
    private List<R> aList;
    // ....
}

@Entity
// ...
public class R{
    @Id
    // ...
    private long id;

    @ManyToOne
    @JoinColumn(name = "id_a", referencedColumnName = "id")
    private A master;

    @ManyToOne
    @JoinColumn(name = "id_b", referencedColumnName = "id")
    private B slave;

    @OneToOne
    @JoinColumn(name = "previous", referencedColumnName = "id")
    private R previous;

    @Column(name = "ordering_index")
    private int ordering;
}

aList .

在创建、更新和删除后,R实体被正确地持久化并在数据库中删除

1. 如果我把B加在A上,A就正确地把B加在了里面 bList
2. 删除B后,R实体被正确删除,但受影响的A实体中仍有B

我试过的

1. 为了看一看,我尝试向 slave 属性,这是个坏主意
2. 我想为负责B实体的EJB修饰CRUD方法:删除后,找到所有受影响的A实体,并删除中的关系 bList公司 so-far > 1) :B无法识别与其相关的A实体
3. 列表 entityManager.merge() 操作=>JPA错误,因为R已经存在(即使我没有级联合并属性?)
4. 列表 无法识别与其相关的实体

编辑:解决方案(草稿)

我附加了解决方案来连接评论和答案的反馈。正如Chris正确提到的,这是关于JPA事务范围的。在继续之前,请先了解一些细节:

1. 在R的设计(数据库和实体定义)中,主从之间存在唯一性约束

在创建和更新A操作时,也更新B实体 )根据克里斯的回答:

public class aEjb{
    // ...
    public void update(A a){

        // by A -> R cascade, all the bList will be updated
        em.merge(a);

        // BUT !!!
        // as the transaction did not end, the newly created
        // relationship do not have a primary key generated
        // yet so if I do:
        for(R r : a.getBList()){
            B b = r.getSlave();
            // I'm here adding r = (null, a, b)
            b.add(r);
            // as r has a null primary key, JPA will try to
            // create it, even if I removed all cascade annotation
            // on b side => I didn't really understand why though
            bEjb.update(b);
            // as there is UNIQUE(a,b) constraint, JPA will
            // throw an exception
        }

        // the solution was to fetch a fresh copy of the 
        // cascaded created R entity. As the primary key
        // is not known yet, I have to go through sth like
        for(R r : a.getBlist()){
            B b = r.getSlave();
            R updatedR = rEjb.findByMasterAndSlave(a, b);
            // I'm here adding updatedR = (123, a, b)
            b.add(updatedR)
            // as updatedR primary key is not null, JPA 
            // won't force any cascade operation, and that's
            // great becaues I don't want any cascade here
            bEjb.update(b);

        }

    }
    // ...
}

附加说明

目前为止 bList公司 列表 是最新的。如果删除B实体,我有一个可用的 循环通过。然而,又出现了一个问题:如果我从a实体中删除了B实体,但只删除了链接,而不删除这些实体中的任何一个,该怎么办?

解决方案是避免这种选择 orphanRemoval = true :

之前:

@Entity
// ...
public class A{
    // ...
    @OneToMany(mappedBy="master", cascade = Cascade.ALL, orphanRemoval = true)
    @OrderBy("ordering")
    private List<R> bList;
    // ....
}

之后:

@Entity
// ...
public class A{
    // ...
    @OneToMany(mappedBy="master", cascade = Cascade.ALL)
    @OrderBy("ordering")
    private List<R> bList;

    @Transient
    private List<R> orphanBList;
    // ....

    public void addB(B b){
        R r = new R(a,b);
        bList.add(r);
    }

    public void removeR(R r){
        bList.remove(r);
        orphanBList.add(r);
    }
}

然后,我继续执行定义的类似EJB操作,以更新受影响的B实体