NHibernate returning duplicate rows from hql named query with object constructors

I have a named hql query which makes use of object constructors for an object that is not mapped (it is only imported)

e.g.

select distinct new NotMappedResultClass(ah.SomeProp1, ah.SomeProp2)
from SomeMappedClass
where ...
order by ah.SomeProp1

The weird thing is, that when I call IQuery.List() in NHibernate, I end up with exactly twice as many rows from NHibernate than from the quer开发者_开发知识库y that NHibernate ran (traced using SqlProfiler).

(In case it matters, the "where" clause does actually involve some subqueries).

Why is NHibernate duplicating the rows coming back from the database?

(I am using NHibernate 1.2.1.4000)

Found the problem.

My project has some odd mappings when it comes to inherited classes.

Basically, SomeMappedClass was abstract, and had its own NHibernate mapping, and there was a derived class SomeDerivedClass (that didn't add any functionality) that was also mapped separately without the "extends" attribute.

This caused NHibernate to issue two sql queries, with different aliases for the same table.

In my case the simple quick and dirty solution was to query from SomeDerivedClass instead of SomeMappedClass, but the more appropriate solution would probably be to modify the mappings / object inheritance.