NHibernate 3.3.1 explicit polymorphism - nhibernate

Question

I use NH 3.3.1.
Suppose simple classes:
public class TestBase
{
public virtual int Id { get; set; }
public virtual string A { get; set; }
}
public class Test : TestBase
{
public virtual string B { get; set; }
}
and mappings for them:
public sealed class TestBaseMap : ClassMap<TestBase>
{
public TestBaseMap()
{
this.Polymorphism.Explicit();
this.Id(a => a.Id).GeneratedBy.Identity();
this.Map(a => a.A);
}
}
public sealed class TestMap :SubclassMap<Test>
{
public TestMap()
{
this.Map(a => a.B);
}
}
Even with Polymorphism.Explicit() specified, NH still left joins Test when querying for TestBase.
var a = this.Session.Get<TestBase>(1);
I don't really need this joining 'cuz will have lots of subclasses.
I checked xml generated by fluent. it's ok, "explicit" clause is there. What am i doing wrong?

Answer 1

I guess that explicit polymorphism is only used in queries, not for session.Get. But I couldn't find any references for this.
Try to not query for the base class, but always have an concrete subclass (which is in most cases a better design anyway):
public abstract class TestBase
{
public virtual int Id { get; set; }
public virtual string A { get; set; }
}
public class TestA : TestBase
{
public virtual string B { get; set; }
}
public class TestB : TestBase
{
public virtual string B { get; set; }
}
var a = this.Session.Get<TestA>(1);

Answer 2

Ok. I've got it. As Stefan supposed, i made abstract TestBase. But since I really needed to query TestBase table without many left joins, i introduced stub class:
public class TestStub : TestBase
{
// nothing
}
This class is absolutely empty. Map:
public sealed class TestStubMap : SubclassMap<TestStub>
{
public TestStubMap()
{
this.Table("TestBase");
this.KeyColumn("Id");
}
}
Now I can query:
var a = this.Session.Get<TestStub>(1)
It produces only one join (TestBase join TestBase). So now i can get my TestBase from db without overhead. I don't like hacks, but if built-in logic doesn't work (polymorphism=explicit), what is left to do.