Question

我在使用Hibernate处理特定场景时遇到了一些困难...

考虑到上面的片段（简化模型），实体A和D已经存在。他们将获得新的儿童B和E，而E也有新的C儿童。然后我打电话给＆＃34;合并＆＃34;实体管理器中的方法。

@Entity
public class A {

    @OneToMany(mappedBy = "a", fetch = FetchType.Lazy, cascade = CascadeType.All)
    private List<B> bList;

}

@Entity
public class B {

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinCollumn(name="ID_A")
    private A a;

    @OneToMany(mappedBy = "b", fetch = FetchType.Lazy, cascade = CascadeType.All)
    private List<E> eList;

}

@Entity
public class C {

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinCollumn(name="ID_E")
    private E e;

}

@Entity
public class D {

    @OneToMany(mappedBy = "d", fetch = FetchType.Lazy, cascade = CascadeType.All)
    private List<E> bList;

}

// The "Double Parented" Children
@Entity
public class E {

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinCollumn(name="ID_B")
    private B b;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinCollumn(name="ID_D")
    private D d;

    @OneToMany(mappedBy = "e", fetch = FetchType.Lazy, cascade = CascadeType.All)
    private List<C> cList;

}

public class Example {
    public void newChildren() {
        A a = getExistingAfromDatabase(); // defined elsewhere
        E e = new E(); // then fills some attributes...
        B b = new B(); // then fills some attributes...

        b.getEs().add(e);
        e.setB(b);

        a.getBs().add(b);
        b.setA(a);

        edit(a);           
    }

    public void edit(A myEntity) {
        EntityTransaction trans = null;
        EntityManager eMngr = getEntityManager(); // this is defined in another place

        try {
            trans = eMngr.getTransaction();
            trans.begin();

            eMngr.merge(myEntity);
            trans.commit();
        } catch (Exception e) {
            if (trans != null && trans.isActive())
                trans.rollback();

            throw new DAOException("Error! " + e.getMessage(), e);
        }       
    }
}

无论我选择合并的第一个实体（A或D），我都得到了相同的异常：org.hibernate.TransientObjectException：object引用未保存的瞬态实例 - 在刷新之前保存瞬态实例：E.b - ＆gt;乙

Hibernate能否使用Cascade处理这个问题？如果是这样，我做错了什么？

非常感谢！

Answer 1

确保你总是同时设置父和子，所以拿A和B你应该在基类中有这种实用方法（例如A）：

public void addChild(B child) {
    child.setA(this);
    this.bList.add(child);
}

此实用程序可以防止您获得此类异常。

Hibernate：将现有实体与新的＆＃34; Double Parented＆＃34;合并。孩子

1 个答案: