The issue:

class A {}
class B extends A {}

class C {
public A clazzA;
}

There is mySQL table (one per hierarchy) that consists class A and class B types.

The heart of the problem that classC.clazzA may contain class B.

IMHO, it's all Ok, but Hibernate when loading class C, set the field clazzA in object of class A though the table have indicator (discriminator) that this concrete row contains class B ( ! )

i.e. objC.classA.getClass().getName() ==> class A (should be class B)

and consequence: B b = (B) objC.classA ==> ClassCastException

?

May be we should talk about implisit polymorphism... ?

Yo, guys, i found the problem!

So, I check "test" directory of Hibernate's sources.
There is FooBarTest.java that contains:


public void testPolymorphism() throws Exception {
Session s = openSession();
Bar bar = new Bar();
s.save(bar);
bar.setBarString("bar bar");
s.flush();
s.connection().commit();
s.close();
s = openSession();
FooProxy foo = (FooProxy) s.load( Foo.class, bar.getKey() );
assertTrue( "polymorphic", foo instanceof BarProxy );
assertTrue( "subclass property", ( (BarProxy) foo ).getBarString().equals( bar.getBarString() ) );
s.delete(foo);
s.flush();
s.connection().commit();
s.close();
}


I create the same test but I haven't used Proxy:


public void testGavPolymorphism() throws Exception {
Session s = openSession();
Bar bar = new Bar();
s.save(bar);
bar.setBarString("bar bar");
s.flush();
s.connection().commit();
s.close();
s = openSession();
Foo foo = (Foo) s.load( Foo.class, bar.getKey() );
assertTrue( "polymorphic", foo instanceof Bar );
assertTrue( "subclass property", ( (Bar) foo ).getBarString().equals( bar.getBarString() ) );
s.delete(foo);
s.flush();
s.connection().commit();
s.close();
}

testout
=======

testPolymorphism - Success
testGavPolymorphism - Error: java.lang.ClassCastException


Use the Source, Luke (C) Star Wars
;)