I have two classes (A and B) where A has a List of B.



The database tables for these two classes would be:



In the 'B' table, the a_id has a foreign key relationship with the id column of the 'A' table.

My question is this: I have a detached instance of A that is populated with several instances of B in its bList. I want to delete all of the instances of B from the instance of A without deleting A. If I were writing strait JDBC code, I would use the following SQL:



What is the best way to do the same with Hibernate? I know of two ways, neither of which is attractive:

Method #1:


The problem with this is that all of the Bs will first be selected from the database before they are deleted. This seems silly because I already have all of the B data in memory within A's bList (remember that I have detached instances). Why would I want to re-select them just to delete them?

Method #2:


This would work fine, except that it will issue one SQL delete statement per instance of B. This also seems silly considering that if I were using JDBC, I would do the same with one SQL delete statement as described above.

So, finally, how do I make Hibernate remove all of the elements of a collection, without removing the collection's parent, in one single SQL delete call?

Thanks!

Hibernate version:2.1.7

Not possible in 2.1, will be possible in next release of 3.0.

Thanks for your quick response!

I was afraid of that. Just for curiosity's sake, what will be the method for doing this when 3.0 is released?

ejb3 style delete by query.

While there is no stable version 3.0, what would be the best way for doing this? I tried method #1 above but it didnt work . I get the following error:

net.sf.hibernate.ObjectDeletedException: deleted object would be re-saved by cascade (remove deleted object from associations): 1363, of class: sonicBiz.DefDNS

if I remove the object from the collection I get:

java.util.ConcurrentModificationException

please disregard. Method 1 above did work. I was doing something wrong

Hi,
can you say me what you did wrong and what is the solution?
I have a problem similar to yours.

Thanks for your answer.

Well, I was actually trying to update a collection . Class1 contains a collection of Class2. I needed to update that collection and the number of elements of the new collection is not necessarily the same as the first one.

Here is what I did:

Class1 class1 = (Class1)session.get(Class1.class, "somekey");

Iterator it = class1.getListOfClass2().iterator();

while (it.hasNext()){
Class2 class2 = (Class2)it.next();
session.delete(class2);

}

Set set = new HashSet();
set.add(new Class2(parameter1, parameter2,...));
set.add(new Class2(...));
set.add(new Class2(...));
set.add(new Class2(...));
class1.setListOfClass2(set);

session.update(class1);

//just deleted the elements and then assigned a new collection to Class1

I hope it helps

Gavin,

I've been trying to find the semantics on how to do this using Hibernate3.0beta1. Could you briefly explain how to do this...or, better yet, provide link to some docs that explain it?

Thanks!