NHibernate offers several cascading options.  Consider the behaviour of each, and choose the best option for your app.

• delete – If an object is deleted, delete all associated objects.
• delete-orphans – If an object is deleted, delete all objects associated to it.  Also when an object is no longer associated with another object, delete it.
• all-delete-orhpans - If an object is saved, deleted, or updated, check associated objects and save, delete, or update them.  Also when an object is no longer associated with another object, delete it.
• save-update – When an object is saved or updated, save or update any associated objects that are now dirty
• all – If an object is saved, deleted, or updated, check related objects and save, delete, or update them
• none – Let’s developers handle cascades by themselves.