I have seen doubts about Nhibernate performance and made some basic tests. After this I have decided that as always it is a question about thinking before acting.
This is my reason for asking you this question.
I am making a system where I need to optimize on this:

For many of my classes I have detailclasses (similar to Order - OrderDetails). I also have detailtypes and each detail have a specific type as a property.
When working with instances of these classes the user either works with lists of details or work with a specific detailtype.
I have in my classes a nonpersistent property: CurrentDetailType.
When this is set there is an opportunity to point directly to an element in the detaillist. Keys in db: ID from class and DetailTypeID.
I have done this in my preNhibernate days where I had a property:
CurrentDetail. This could be instantiated directly without iterating through the detaillist and finding the detail.
Ie.: the class maps in two ways to the same class. one-to-one and one-to-many.
Is it possible somehow to achieve the same with NHibernate?
Thanks beforehand. And a lot of applause to all of you who works on NHibernate and makes our life much easier.

Can you post the mapping files and the classes as I'm not quite sure of the relationships yet.