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lhoriman
 Post subject: Deleting entities and their relationships
PostPosted: Mon Sep 15, 2003 7:43 pm 
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From a #hibernate irc conversation today:

You have two entities, EntityA and EntityB. They have a bidirectional many-to-many relationship, EntityB
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gavin
 Post subject:
PostPosted: Mon Sep 15, 2003 9:34 pm 
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The answer is "yes" to the first, and "no" to the second.
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lhoriman
 Post subject:
PostPosted: Tue Sep 16, 2003 3:19 pm 
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gavin wrote:
The answer is "yes" to the first, and "no" to the second.


Is there any plan to make this behavior more consistent?

In the case of the second situation (deleting the inverse entity), is there any efficient way to delete relationship participation without resorting to JDBC?

Thanks,
Jeff
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gavin
 Post subject:
PostPosted: Tue Sep 16, 2003 3:39 pm 
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How is this inconsistent??

The semantics of inverse="true" are currently quite clear. i.e. Don't propagate changes made to "this end" of the association.


No, I will not be changing anything.
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lhoriman
 Post subject:
PostPosted: Tue Sep 16, 2003 3:48 pm 
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gavin wrote:
How is this inconsistent??

The semantics of inverse="true" are currently quite clear. i.e. Don't propagate changes made to "this end" of the association.

No, I will not be changing anything.



Then what should we do for the use case I described?

EntityA many-to-many EntityB, EntityB is inverse

I want to delete an instance of EntityB.

Jeff
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gavin
 Post subject:
PostPosted: Tue Sep 16, 2003 3:59 pm 
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iterate over the associated EntityB instances and remove the association at that end. This is quite consistent with how other one-to-many bidirectional associations work.


Now, note: for many-to-many associations, you don't necessarily need to do the inverse="true" thing. You can make it work perfectly well, leaving both ends inverse="false". But then you need to make sure you don't change both ends of the association in one transaction.
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lhoriman
 Post subject:
PostPosted: Tue Sep 16, 2003 4:25 pm 
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Ok, cool. Don't use inverse for many-to-many, that makes sense.

Now to make it more complicated:

EntityA has a Map of EntityB to a component.

I want to delete an instance of EntityB.

How can I do this?

This is a real-world problem for me which I haven't addressed yet. I've been assuming "delete the relationship with JDBC, delete the entity with Hibernate, and evict the relationship cache", which is inelegant but ok for my purposes.

Jeff
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gavin
 Post subject:
PostPosted: Tue Sep 16, 2003 9:21 pm 
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you should *still* be able to make this association bidirectional. But map the reverse association as a simple many-to-many Set, and do use inverse="true". That way, you can "get to the other end", and then remove the association from the other end.
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lhoriman
 Post subject:
PostPosted: Wed Sep 17, 2003 5:28 pm 
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gavin wrote:
you should *still* be able to make this association bidirectional. But map the reverse association as a simple many-to-many Set, and do use inverse="true". That way, you can "get to the other end", and then remove the association from the other end.


That would mean loading every instance of EntityA (and fully populating its Map) which has a relationship with the EntityB that I'm deleting... that could be millions of EntityA objects, each of which will likely have 100-200 map entries. Ouch.

Would it be possible to achieve the same effect (without adding bidirectionality) using a query like this?

Code:
List fixList = sess.find("from EntityA a where a.theMapOfBs[?] is not null", b.getId(), Hibernate.LONG);


Not that it would solve the performance problem...

Jeff
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jzhuo
 Post subject:
PostPosted: Fri Sep 26, 2003 3:09 am 
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I have a demo to test deleting many-to-many entity,it like following:

Code:
//this setting is for entity Operation
<set name="users" table="T_UserRights" lazy="true" inverse="true" cascade="none">
      <key column="OperID"/>
      <many-to-many class="test.User" column="UserID" outer-join="auto"/>
</set>

//This setting is for entity User
<set name="operations" table="T_UserRights" lazy="true" cascade="none">
  <key column="UserID"/>
  <many-to-many class="test.Operation" column="OperID" outer-join="auto"/>
</set>


T_User: UserID UserName ...
T_Operation: OperID OperName ...
T_UserRights: UserID OperID

Now, I get a User instance from hibernate, and delete it, this code is:
Code:
//session is a variable of Session class
User user = (User) session.load(User.class, "test");
Transaction tx = session.beginTransaction();
session.delete(user);
session.flush();
tx.commit();


when the program run these codes. it throws the following exception:
Code:
net.sf.hibernate.HibernateException: Flush during cascade is dangerous - this might occur if an object was deleted and then re-saved by cascade (remove deleted object from associations)

   at net.sf.hibernate.impl.SessionImpl.flush(SessionImpl.java:2174)

   at net.sf.hibernate.impl.SessionImpl.save(SessionImpl.java:626)

   at net.sf.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:1216)

   at net.sf.hibernate.engine.Cascades$5.cascade(Cascades.java:105)

   at net.sf.hibernate.engine.Cascades.cascade(Cascades.java:280)

   at net.sf.hibernate.engine.Cascades.cascadeCollection(Cascades.java:373)

   at net.sf.hibernate.engine.Cascades.cascade(Cascades.java:296)

   at net.sf.hibernate.engine.Cascades.cascade(Cascades.java:331)

   at net.sf.hibernate.impl.SessionImpl.preFlushEntities(SessionImpl.java:2470)

   at net.sf.hibernate.impl.SessionImpl.flushEverything(SessionImpl.java:2188)

   at net.sf.hibernate.impl.SessionImpl.flush(SessionImpl.java:2177)

   at test.Test.run(Test.java:132)

   at test.Test.main(Test.java:38)


please help me! thanks!
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csmklee
 Post subject: have u tried
PostPosted: Fri Sep 26, 2003 4:35 am 
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Joined: Mon Sep 22, 2003 7:16 am
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setting both inverse=false
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jzhuo
 Post subject: Re: have u tried
PostPosted: Fri Sep 26, 2003 4:42 am 
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Joined: Fri Sep 26, 2003 2:50 am
Posts: 32
csmklee wrote:
setting both inverse=false


I have tried it to set both inverse=false, the result is same!

BTW, I set the 'set' properties like the examples Author/Work in reference manual CHAP16, it can not work too.

UNHAPPY!!!
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