删除Tapestry5给出的休眠实体:“具有相同标识符值的其他对象已与会话关联”[重复]

可能重复:
Hibernate: different object with the same identifier value was already associated with the session

删除实体时出错。我一次只在一个组中拥有用户,所以在用户类中这是一种多方面的关系。在page类中,我有一个属性组:

@Property @Persist private Group group;

在页面激活时填充:

public void onActivate(Group g) {
    group = g;
}

单击删除操作链接时,将执行以下操作:

@CommitAfter
public ListBillingUserGroups onActionFromDelete() {
    for (User u : getUsersInGroup())
        u.setGroup(null);
    session.delete(group);
    return listPage;
}

public List<User> getUsersInGroup() {
    Criteria c = session.createCriteria(User.class)
        .add(eq("company", ctx.getUser().getCompany()))
        .add(eq("group", group));
    return c.list();
}

当该组中没有用户时,将执行删除操作,浏览器将重定向到列表页(如预期)。但是,如果组中有用户,则会从休眠中引发异常,并显示消息:

a different object with the same identifier value was already associated with the session: [my.package.Group#10]

使用stacktrace:

org.hibernate.engine.StatefulPersistenceContext.checkUniqueness(StatefulPersistenceContext.java:613)
org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:121)
org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:74)
org.hibernate.impl.SessionImpl.fireDelete(SessionImpl.java:793)
org.hibernate.impl.SessionImpl.delete(SessionImpl.java:771)
... my code ...

如果将OnActionFromDelete方法替换为:

@CommitAfter
public ListBillingUserGroups onActionFromDelete() {
    for (User u : getUsersInGroup())
        System.out.print(" >> " + u.getGroup());
    session.delete(group);
    return listPage;
}

错误仍然会发生(与获取约束语音异常相反),但如果我将其替换为:

@CommitAfter
public ListBillingUserGroups onActionFromDelete() {
    session.delete(group);
    return listPage;
}

我得到了违反约束的异常。

因此,它的行为就好像调用getAllUsersInGroup方法会将Group对象更改为表示同一实体(同一类、同一ID)的另一个对象。我做错了什么有什么暗示吗?