如何删除双向多对多关联

Problem:

问题：

I have many-to-many association between two entities A and B. I set A entity as an owner of their relationship(inverse=true is on A's collection in b.hbm.xml).

我在两个实体A和B之间有多对多的关联。我将一个实体设置为它们关系的所有者（inverse = true在b.hbm.xml中的A集合上）。

When i delete an A entity, corresponding records in join table are deleted.
When i delete an B entity, corresponding records in join table are not deleted (integrity violation exception).

删除A实体时，删除连接表中的相应记录。当我删除B实体时，连接表中的相应记录不会被删除（完整性违规例外）。

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Let's consider some very simple example:

让我们考虑一些非常简单的例子：

class A{  
    Set<B> bset=new HashSet<B>();
    //...
}  

class B{  
    Set<A> aset=new HashSet<A>();  
    //...
}

File a.hbm.xml [m-to-m mappings only]:

文件a.hbm.xml [m-to-m映射]：

<set name="bset" table="AB">  
    <key name="a_id"/>  
    <many-to-many column="b_id" class="B"/>  
</set>

File b.hbm.xml [m-to-m mappings only]:

文件b.hbm.xml [m-to-m映射]：

<set name="aset" table="AB" inverse="true">  
    <key name="b_id"/>  
    <many-to-many column="a_id" class="A"/>  
</set>

Database relations:

数据库关系：

A(id,...)  
B(id,...)  
AB(a_id,b_id)

Suppose that we have some records in AB joint table. For example:

假设我们在AB联合表中有一些记录。例如：

AB = {(1,1),(1,2)}

AB = {（1,1），（1,2）}

where AB= { (a_id , b_id) | ... ... }

其中AB = {（a_id，b_id）| ......}

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Situation 1 - works probably because A is owner of AB relationship:

情况1 - 可能因为A是AB关系的所有者而起作用：

A a=aDao.read(1);  //read A entity with id=1  
aDao.delete(a);    //delete 'a' entity and both relations with B-entities

Situation 2 - doesn't work:

情况2 - 不起作用：

B b=bDao.read(1);   //read B entity with id=1  
bDao.delete(b);     //foreign key integrity violation

On the one hand, this is somehow logical to me, because the A entity is responsible for his relation with B. But, on the other hand, it is not logical or at least it is not orm-like solution that I have to explicitly delete all records in join table where concrete B entity appears, and then to delete the B entity, as I show in situation 3:

一方面，这对我来说是合乎逻辑的，因为A实体负责他与B的关系。但是，另一方面，它不符合逻辑，或者至少它不是类似orm的解决方案，我必须明确删除连接表中出现具体B实体的所有记录，然后删除B实体，如我在情境3中所示：

Situation 3 - works, but it is not 'elegant':

情况3 - 工作，但不是'优雅'：

B b=bDao.read(1);  
Set<A> aset=b.getA();     //get set with A entities
Iterator i=aset.iterator();  

//while removes 'b' from all related A entities  
//while breaks relationships on A-side of relation (A is owner)
while(i.hasNext()){  
    A a=i.next();  
    a.bset.remove(b);   //remove entity 'b' from  related 'a' entity 
    aDao.update(a);       //key point!!! this line breaks relation in database
}  
bDao.delete(b);           //'b' is deleted because there is no related A-entities

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So, my question: is there any more convenient way to delete no-owner entity (B in my example) in bidirectional many-to-many association and all of his many-to-many relations from joint table?

所以，我的问题：是否有更方便的方法来删除双向多对多关联中的无所有者实体（在我的例子中是B）以及他从联合表中获得的所有多对多关系？

1 个解决方案

#1

I do not see what is not elegant about the code. It works fine in all cases and does not do any extra stuff which it is not supposed to. When I say A is owning side is a relationship AB, this would imply that creating or deleting the relationship lies in the hands of A. B has no say in the relationship. So if I want to move B somewhere else, A has to let go of B before B can be moved away. Hence, when choosing the owning side you should consider what you are going to do with the objects.

我没有看到代码有什么不优雅。它在所有情况下都能正常工作，并且不会做任何不应该做的额外的事情。当我说A拥有的一方是AB的关系时，这意味着创建或删除关系掌握在A的手中.B在关系中没有发言权。因此，如果我想将B移动到其他地方，A必须放弃B才能将B移开。因此，在选择拥有方时，您应该考虑将要对象进行的操作。