19.5.4. One shot delete
Deleting collection elements one by one can sometimes be extremely inefficient. Hibernate knows not to do that in the case of an newly-empty collection (if you called
list.clear(), for example). In this case, Hibernate will issue a single DELETE.
Suppose you added 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.
However, suppose that we remove eighteen elements, leaving two and then add thee new elements. There are two possible ways to proceed
- delete eighteen rows one by one and then insert three rows
- remove the whole collection in one SQL
DELETEand insert all five current elements one by one
Hibernate cannot know that the second option is probably quicker. It would probably be undesirable for Hibernate to be that intuitive as such behavior might confuse database triggers, etc.
Fortunately, you can force this behavior (i.e. the second strategy) at any time by discarding (i.e. dereferencing) the original collection and returning a newly instantiated collection with all the current elements.
One-shot-delete does not apply to collections mapped
inverse="true".
