Hello,

it seems to me that NHibernate doesn't want return the collection of child objects that are in the same class hierarchy as the parent.

In the following example I have base class QuestionBase and 2 derived classes Question & Group.
Object Group contains collection of Question objects.

I have created one group in the DB and inserted a few Questions in the Group.
But when I retrieve this Group via NHibernate and look at it's Questions collection, it is always empty.

What is the reason?

Mapping file:

Your mapping is a bit strange, you have Group.Id and the key for Group.Questions mapped to the same column. You probably want the collection key to be GroupID.

Sergey, thank you for the help!

But I'm not sure that the key of the collection should be GroupID.

I have base class QuestionBase. It's identifier is QuestionID.
The same identifier have derived classes Question & Group.

I want retrieve all Questions in the Group. For this purpose
I use collection Questions in subclass Group with key QuestionID
(the id of Group).

And GroupID is database field (foreign key) of Question objects.

Please let me know if I'm not right.

Maybe the collection is empty because GROUP - is reserved word in SQL?

But I don't see an error on the page.

Best regards,
Sergey





> Your mapping is a bit strange, you have Group.Id and the key for
> Group.Questions mapped to the same column. You probably want the
> collection key to be GroupID.

How do you select the questions that belong to the group with ID 1? Do you do 'select * from Question where QuestionID = 1' or do you do 'select * from Question where GroupID = 1'? The field that you use to "identify" the collection (QuestionID or GroupID) is called collection key in NHibernate, and that's what the <key> element should map to.