Can anyone tell me if there is such a feature in NHibernate?

I have two associated objects lets name them Parent and Child. Child object has a reference to Parent object. Child object contains Id of Parent object in database, but objects are not linked with foreign key. My query fetches all Child objects from the table and also takes all Parent objects. All works fine if there is Parent object for each Children. But if the Parent object doesn't exist for any Child object then NHibernate generates exception. Is there is a way to make NHibernate assign null value to a Parent property of a Child object if Parent row doesn't exist for this Child without generating exception?

In your Child mapping you probably have a many-to-one mapping for Parent. Set the not-null attribute to false.

No, it doesn't help :( I believe it isn't work because the value of a Parent Id column in a Child row isn't NULL but a specific not existing in Parent table number. Is there a way to make it work without changing all non-existing Id values to NULL?

No, this feature is not present in NHibernate currently.

Okay, I see. Actually I found a solution that helps me to do what I want without using triggers. I created a View which uses LEFT OUTER JOIN to merge tables and I can automatically put the value NULL to Parent Id column in all Child rows. But now I have a different problem, 'cause I had to change the value of a TABLE attribute in mapping file to table view. So now it is impossible for me to insert records of type Child. Can I somehow tell NHibernate that he must use my table view for fetching records and original table for inserting/updating?

In the end I just created trigger, which nullify all reference to Parent table if someone deletes Parent row.