Are one-to-many associations required to be two-way? Let's say I have a one-to-many association from a Foo object to a set of Bar objects. My application requires only one-way navigation, from a Foo object to its Bar objects.

Does NHibernate nonetheless require me to (a) include a Foo property in my Bar class, and (b) include a <many-to-one> mapping in the Bar mapping file? Or can I simply use a <set> mapping in the Foo object (and no Foo property in my Bar object), since my business requirements specify one-way navigation?

Thanks for your help!

David Veeneman
Foresight Systems

I think the answer is yes with one exception. If you allow the foreign key to Foo to be nullable in the Bar table then NHibernate will persist the many side with an insert to Bar then an update to set the foreign key.

I'd be happy to hear that this isn't the case because I don't like this answer either. The pattern I've adopted is to expose the collection as read only and use Add and Remove methods to control the collection contents. These methods would be responsible for setting Bar.Foo on the Bar being added or removed.

Nothing to add to greenmtboy answers. You might want to read this

http://nhforge.org/doc/nh/en/index.html#example-parentchild

This will give you more information about that case.