Of all the greatness in NHibernate, there is one aspect I find not so great; XML mapping files. I'd much prefer to do the mapping in code where it can be compiled, built, and tested with less trouble.

Looking at the Binder class, it seems like I could build up an equivalent PersistentClass and add it to the Mappings.

Does this seem reasonable? If so, are there any suggestions to go about doing it?

There are two attribute-based solutions. One is NHibernate.Mapping.Attributes in the NHibernateContrib package, and the other is Castle's ActiveRecord solution.

I've looked at attributes and active record. Both solutions force the POCOS to depend on NHibernate. I'd like to avaoid this too.

Building up the mappings in code, seperate from the POCOS, is what I'd really like.

You have to add a reference to NHibernate.Mapping.Attributes.dll (not NHibernate.dll)!
And even if you had to add a reference to NHibernate.dll, conceptually, there will still be no usage of NHibernate.

Another "extreme" solution would be to have a separated set of class with attributes (so, you will have to maintain your domail model and update these "mapped classes" whenever your mapping change).

Anyway, do you have another possible solution for your issue?

Right. I understand that the attributes are unintrusive, but they still require a reference to the dll and using statement in all my POCOs. This is a violation of the Dependency Inversion Principle. It means I can't build without NHibernate or NHibernate.Mapping.Attributes. I'd like a DLL containing all my domain classes that has no external dependency.

I've considered the "extreme" solution and found it unpalatable. Using XML mapping files also provides the decoupling I want, it

As far as I know, neither NMA or AR (or NHibernate for that matter) was explicitly designed using DI. Also, DI doesn't help when you need to use interfaces in the dependent assembly. DI is about object dependencies, not assembly dependencies. You could load objects by reflection, but attributes won't work that way.

If you want an attribute-based mapping solution that you don't have to write yourself, you have to reference an external dll of some kind. Otherwise, you have to do the mapping yourself. I know of no other solution.

Seems like a very expensive requirement. What is the reason for it? License issues?