Hi All, I have been having problems with nested collections. I have just found this comment on the web 'Unfortunately hibernate doesn't handle collections inside collections' at http://www.xwiki.org/xwiki/bin/view/Dev/UnorganisedFeedback

Is this true, that you cannot use collections inside collections?

Thanks

Paul :-)

Thats correct. It's not very good OO anyways.

Hi Michael, thanks for the quick reply. I'm interested in why you think that it is not good OO? For example I have an Account object which contains multiple AddressBook objects & a user can add as many as they wish. These AddressBook objects need to contain multiple Contact objects which contain the info about each contact. How else would one model this?

Paul

Exactly as you described it.

But then surely I have a collection of Contact objects inside a collection of AddressBook objects inside an Account object, which is a collection inside of a collection which Hibernate cannot cope with & which you said was not very good OO? And is the problem I have been struggling with since attempting to port my app from CMP Entity Beans to Hibernate.

Paul :-)

This is not what a "nested collection" is. A nested collection would be this:



Hibernate can perfectly handle the example i posted.

OK. Thanks. It's me then :-) I've been having a real nightmare, with which should be my primary & which should be my inverse mapping & how I manage adding & removing things. I had a really odd experience, where in my junit test I add an AddressBook to the Account, then get the collection of AddressBooks from the Account, get my AddressBook object back from the collection & then call myCollection.contains(myAddressBook) & it returns false!!! Even though I just obtained the object from the same collection! I'll have to soldier on & try to figure it out.

Thanks Michael :-)
Paul

check your equals/hashCode implementation, thats the bug most likely. look here http://www.hibernate.org/109.html

Thanks Michael, I'll check that out, as my equals & hashcode at the moment do use the id!

Paul :-)

Does Hibernate still have the nested collection limitation in its latest versions of Hibernate that was indicated in this 2004 posting?