NHibernate SQL Server Identity Columns - Use or Not Use

Question

I work with SQL Server, and most tables have identifier columns of type int. And now I just stumbled upon a book that says that this mechanism is not recommended. What are the downsides / pros of using identity columns when using NHibernate as an ORM?

Answer 1

I'm not an NHibernate expert, but as I understand it, using identity columns breaks UnitOfWork and causes extra round trips to the database.

Fabio Molo (then NHibernate project manager, I'm not sure if he still has one) has a blog post where he explains this in detail:
Identity: Endless Story

Here is another (longer) blog post with sample code:
NH2.1.0: Generator Behavior Explained

However, note that both blog posts are about three years old and talk about NH 2.1.0, and the current version to date is NH 3.3. But I suppose that the problem described by Fabio still exists today.

Answer 2

It doesn't matter if they are an identifier column or not. The role of ORM is to map data objects in the database so as not to dictate the structure / design of the database. I used an implementation with identity columns and it works fine.