one-shot delete is different for bag?

tahirawan · **Joined:** Mon Sep 01, 2003 12:31 am **Posts:** 5

Hi,

I am trying to do one-shot delete and found the following in section 12.4 of the document.

"Suppose we add a single element to a collection of size twenty and then remove two elements. Hibernate will issue one INSERT statement and two DELETE statements (unless the collection is a bag). This is certainly desirable. ".

Question is why the behavior is different for a bag. I am using a bag for my parent/child relationship. Does it mean I should use some other type (e.g., set etc.)? Or is there another way to clear a collection that's mapped using a bag?

I want to do a one-shot delete the existing collection and add a new collection during an update.

Thanks,
Tahir

steve · **Posted:** Mon Sep 01, 2003 12:50 pm

When you use a bag, Hibernate has no way to uniquely identify each row, thus it cannot efficiently perform single row operations.

The term on-shot-delete actually refers to the opposite of what you quote from the docs. A one-shot-delete operation is deleteing all elements in a collection and then re-inserting them.

One-shot-delete is available for all Collection types. To apply a one-shot-delete, do something likes this:

Code:

Parent parent = session.load( Parent.class, parentId );
List children = new ArrayList();
children.add( child1 );
children.add( child2 );
parent.setChildren( children );

Or if you map using a list or set and want to avoid using one-shot-delete semantics, then do something like:

Code:

Parent parent = session.load( Parent.class, parentId );
parent.getChildren().add( child1 );
parent.getChildren().remove( child2 );

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