CMP ejbRemove(): Underlying collection has been modified.

[sergeibatiuk]

Hello,

I have a TreeNode bean that implements a hierarchical structure. It has a CMR field parent, with type of TreeNode. There is also a CMR field children, with type of java.util.Collection. Both of these fields comprise a single one-many relationship.

My ejbRemove() method is as follows:

public void ejbRemove() {
Iterator children = getChildren().iterator();
while ( children.hasNext() ) ( ( TreeNode )children ).remove();
}

However, I get the "Underlying collection has been modified" exception. Is it OK?

If I add an ejbSelect method called "ejbSelectChildren( TreeNode parent ); with a query "SELECT OBJECT(tn) FROM TreeNodeBean tn where tn.parent=?1", and redefine my ejbRemove() method as

public void ejbRemove() {
Iterator children = ejbSelectChildren( ( TreeNode )entityContext.getEJBLocalObject() ).iterator();
while ( children.hasNext() ) ( ( TreeNode )children ).remove();
}

Everything works fine.

Why can't I just use a collection return with getChildren()? Is it a bug or a feature?

Thanks in advance.
Sergei Batiuk.

[sergeibatiuk]

There has been a mistake in my previous message:

my ejbRemove() method, that doesn't work (but should work in my opinion):
---------------------------------

public void ejbRemove() {
Iterator children = getChildren().iterator();
while ( children.hasNext() ) ( ( TreeNode )children.next() ).remove();
}


ejbRemove() that works, but requires addition ejbSelect() method:
---------------------------------
public void ejbRemove() {
Iterator children = ejbSelectChildren( ( TreeNode ) entityContext.getEJBLocalObject() ).iterator();
while ( children.hasNext() ) ( ( TreeNode )children.next() ).remove();
}

---------------------------------
All this wouldn't be an issue if cascade-delete worked fine (which doesn't work, it seems, in BEA Weblogic 7 properly too).

[timfox]

You need to remove the item from the iterator
ie iter.remove(), just before the call to yourObject.remove().
you are getting a collectionmodifiedexception since your call yourObject.remove() removes the object from the collection you are currently iterating through thus making it invalid.
This is a side-effect of what the ejb2 spec mandates for what happens when you remove an entity.
There is a whole section in the ejb2 spec on the correct semantics for adding and removing entities from cmr relations.