Okay here is an interesting situation that I am not sure has a solution:

Assume 2 tables and 1 many/many table as:
Person
personID
firstname

Address
addressID
city
IsPrimaryAddress

Person_address
personID
AddressID

I have a person object and an address object. The default of course would be for Person object to have a List of Addresses property.

However, I really just want person to have a single Address property were the address is "IsPrimaryAddress == true". Now I could solve this on the object by making the list property private and providing a non-mapped property that uses the private property collection. But is there a cleaner mapping way to do this ?

I do this in my schema, so my understanding is that the answer is "no". I also limit the collection to the pertinent object using a where="IsPrimary = 1" attribute in the list mapping.

I don't think there is any other mechanism, but I too would love to be proven wrong ;)