I have the following problem:

There is a base class 'A' and its inheritor one 'B'.
These classes are both mapped on the table 'C'.

Supposed, there are two records in the table 'C'.

If we select data of objects 'A' we get 4 records.
although we get 2 records for the objects 'B'.

What may problem be in ?
Note: I'm using NHibernate 1.2
Thanks in advance.

I assume you don't have a discriminator value:

when selecting A you select A and all inheritors, since your table contains two rows which (i assume can be both A's and B's) it returns 2 A instances and 2 b instances. The same result would you get if you did for instance:

How can i resolve this problem?

In my book it isn't a "problem" its just how polymorphism works :-)

But for performanceoptimizations you can take a look at the suggestions in this post:

http://forum.hibernate.org/viewtopic.ph ... 56#2373556

I need to get 2 records for 'A' and 'B' objects (

An instance of B is also of type A as far as i known HQL queries don't have any operators to ensure that you only get superclass'es. Try reading chapter 11.6 in the nHibernate reference manual

Thanks for your quickly answering my question.
You clarified a lot of nuances.