Hibernate在级联上删除对象 [英] Hibernate delete objects on cascade

问题描述

对于cascade =delete是如何工作的，我很困惑。我在City映射文件中以下列方式定义了映射：

 < set inverse =truename =client cascade =delete> 
< key> 
< column name =id_name/> 
< / key> 
<一对多等级=model.Client/> 
< / set> 
  

类Client拥有一个City类的外键。

所以当我运行时：

  List object = null; 
尝试{
 org.hibernate.Transaction tx = session.beginTransaction（）; 
 try {
 session.delete（from city where row_id =+ row_id and table_id =+ table_id）; 
} catch（Exception e）{
 e.printStackTrace ）; 
} 
} 
  

如果所有的客户端都被删除，或者我是否需要处理它？我是否将查询作为方法参数正确传递给会话的delete（）方法？感谢您的帮助。
最好的问候，
sass。

解决方案

我对cascade =delete的工作方式略有困惑（...） >

级联删除操作意味着如果 delete 一个父项，这个操作将会沿着这个关联传播，所以在你的情况下，删除一个 City 实体应该被传播到 Client s。

所以当我运行时（...）所有的客户端都应该被删除

使用 HQL查询字符串的 Session＃delete（String）方法，执行它，遍历结果并调用 Session＃delete（Object）在每个对象方面级联（因此，如果您的查询实际上是HQL查询，则客户端将被删除）。

但是这个方法是旧的，并且在Hibernate 3中已经被弃用了（并且转移到了经典的 Session 界面），我并不真的推荐它1 + N操作，并且删除大量结果的效率非常低）。

如果这是一个问题，那么首选Hibernate提供的批量删除支持：

  int deleteCount = session.createQuery（从Foo删除where bar =：bar）
 .setParameter（bar，bar）; 
 .executeUpdate（）
  

但是请注意批量删除有限制：

• 您无法使用别名。
  
• 查询中没有内连接（尽管可以在where子句中使用子查询）。


• 批量删除不会级联（并且不会处理连接表）。

因此，对于批量删除，您必须在 City Client C $ C>。但是，表演要好得多。

PS：你需要 commit（）错误处理，即catch块中的 rollback（））
$ b

引用

• Hibernate核心参考指南
  
  
  
  
  • 14.4。 DML风格的操作
  
  

I'm sligthly confused as to how the cascade="delete" works. I defined the mapping in the following way in the City mapping file:

<set inverse="true" name="client" cascade="delete">
  <key>
    <column name="id_name"/>
  </key>
    <one-to-many class="model.Client"/>
 </set>

The class Client has a foreign key to a class City.

So when I run:

List object = null;
try {
   org.hibernate.Transaction tx = session.beginTransaction();
   try {
       session.delete("from City where row_id=" + row_id and table_id = " + table_id);
   } catch (Exception e) {
       e.printStackTrace();
   }
}

Should all the clients be deleted as well or do I have to handle it somehow? Am I passing the query as a method parameter correctly to the delete() method of a session? Thanks for any help. Best Regards, sass.

解决方案

I'm slightly confused as to how the cascade="delete" works (...)

Cascading a delete operation means that if you delete a parent, the operation will be propagated along the association. So in your case, deleting a City entity should be propagated to the Clients.

So when I run (...) Should all the clients be deleted as well

The Session#delete(String) method that takes a HQL query string, executes it, iterates over the results and calls Session#delete(Object) on each object respect cascading (so the Clients will be deleted if your query is really a HQL query).

But this method is old and has been deprecated in Hibernate 3 (and moved to the "classic" Session interface), I do not really recommend it (it performs 1+N operations and is pretty inefficient to delete a huge number of results).

If this is a concern, prefer the bulk delete support offered by Hibernate:

int deleteCount = session.createQuery("delete from Foo where bar = :bar") 
    .setParameter("bar", bar);
    .executeUpdate()

But note that bulk delete has restrictions:

• You can not use aliases.
• No inner joins in the query (although you can use subselects in the where clause).
• A bulk delete does not cascade (and won't take care of join tables).

So with a bulk delete, you'd have to delete the Client before the City. But performances are much better.

PS: You need to commit() at some point (and also improve your error handling i.e. rollback() in the catch block)

References

• Hibernate Core Reference Guide
  • 14.4. DML-style operations

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