Prepare for a random thought > 140 chars:
I just read Ayendes post where he debates why we should not put an abstraction on top of NHibernate.
The reason to do such a thing would be to avoid coupling your code to the persistence layer. This in itself is not a bad idea until you take a deeper look at what is required to make a useful abstraction.
A simple persistence interface on top of NHibernate would make it easy to change the persistence layer but
- What happens when you need other features from NHibernate. Will you add it to the abstraction layer ? Not a very solid abstraction really.
- NHibernate is already an abstraction on top a relational database. Do you want to add another one ?
The term “Leaky abstraction” comes to mind.
