Hibernate version: 2

Hi, I am a newbie in hibernate and definitely confused.

I have a classic many-to-many relation (e.g. Category and Item). The relational table doesn't have it's own id but uses a combined key consisting of the 2 foreign keys (e.g <CAT_ID, ITEM_ID>). Both collections (Category.items, Item.Categories) are lazy loaded.

I want to retrieve the Item.Categories ids without loading the categories collection.

My first approach was using a query like

My second approach trying to avoid inner selections was

Both of them worked fine, but then I was urged to use filtering, so here are my questions :

1) Is there any point trying to use filtering in this case if the collection may not be initialized or referenced (net.sf.hibernate.LazyInitializationException)?
2) If yes how can I do this? What filter should I use (e.g. "select this.id").
3) What is the practical difference with the previous approaches?

Thanks in advance for your time.

First of all if you have declared many to many relationship in both direction you can simply do:

item = session.load( Item.class, id );

Set<Category> categories = item.getCategories();

that is all.

If for some reason there is not item.categories and only category.items than you may use this query:

select c.id from Category c join c.items i where i = :chosenItem

Please rate if that helped.

Thanks! It seems to be working now. Actually I missed the loading part. When I loaded the item object and then applied a filter "select this.id" on the categories collection, it worked fine.

On the other hand, in terms of optimization, since joining is not avoided, shouldn't be better to choose the 2nd approach (HQL join query), in order to avoid the loading overhead?