HQL query results "cannot be used in this generic collection" when returning a subclass

Given the following:

A Company has a collection of Product objects.

An Area has a collection of Product objects.

Any given Product has a Company and an Area.

SpecialProduct is a subclass of Product.

I'm using the following HQL query in NHibernate.

// return all SpecialProperty objects for a given company and area.
IQuery query = session.CreateQuery("select product from Company as company " +
    "join company.Products as product " +
    "join product.Area as area " +
    "where company.Id = :coId " +
    "and area.Id = :arId " +
    "and product.class = MyNamespace.DomainModel.SpecialProduct ")
    .SetInt64("coId", companyId)
 开发者_StackOverflow   .SetInt64("arId", areaId);
IList<SpecialProduct> specialProducts = query.List<SpecialProduct>();

When the 2nd statement above executes, I get an error stating:

Could not execute query[SQL: SQL not available] The value "SpecialProduct" is not of type "MyNamespace.DomainModel.SpecialProduct" and cannot be used in this generic collection.

Parameter name: value

(Note that the object shows in the message above as "SpecialProduct" because of a ToString() override in the SpecialProduct class.)

If I change the statement to return a list of the superclass, Product, like so...

IList<Product> products = query.List<Product>();  

...then I don't get the error and a single matching object is returned in the list. Examining this object in the debugger I see that appears to be, in fact, a SpecialProduct according to the ToString() override, but looking closer I see that it is an NHibernate proxy class. If I try casting the object to SpecialProduct, the cast fails. Hmmm...

I also checked in the database itself and confirmed that the record was saved as a SpecialProduct (based on the fact that there is a matching record in the joined-subclass table).

I need to get the results as a generic collection of SpecialProperty objects.

Any ideas on why this isn't working?

This is by design. NH proxies inherit from the base type, not subclasses.

Hopefully, this link will help.