Can anyone tell me if it is possible to use a discriminator column as part of a unique-key? We have a few classes that would benefit from a "one table per class hierarchy" model, but we currently require specific fields (a user given ID is one example) to be unique only to that concrete class. Currently we are having to use "one table per subclass" to satisfy our uniqueness needs, but it seems like the wrong solution to the problem.

We are currently using NHibernate 1.2.1