In Secion 6.4.1 of "Hibernate in action" the authors speak about some nuances of polymorphic many-to-one associations noting along, the way, that when such associations are mapped lazily there are limitations on the use of casting due to the use of proxies:

.. if BillingDetails was mapped with lazy="true", Hibernate would proxy the billingDetails association. In this case, we wouldn’t be able to perform a typecast to the concrete class CreditCard at runtime, and even the instanceof operator would behave strangely:
User user = (User) session.get(User.class, uid);
BillingDetails bd = user.getBillingDetails();
System.out.println( bd instanceof CreditCard ); // prints "false"
CreditCard cc = (CreditCard) bd; // ClassCastException!


Then they propose a way of dealing with this isse, which is based on knowing the expected runtime type:

User user = (User) session.get(User.class, uid);
BillingDetails bd = user.getBillingDetails();
// Get a proxy of the subclass, doesn't hit the database
// The below code assumes the knowledge of the expected
// runtime type of the bd instance.
CreditCard cc = (CreditCard) session.load( CreditCard.class, bd.getId() );
expiryDate = cc.getExpiryDate();

What they don't explain is how to dynamically figure out the runtime type of a given BillingDetails object. Consider this code:

User user = (User) session.get(User.class, uid);
BillingDetails bd = user.getBillingDetails();
// Suppose I don't know what dynamic type of the bd POJO is.
// Depending on the runtime type, I'd like to use different execution paths:
if (bd instanceof CreditCard) {
// process bd as a credit card;
}
else if (bd instanceof BankAccount) {
// process bd as a bank account;
}

Does Hibernate support this usage scenario for lazy associations?

Thanks in advance,
Andrei.

have you tried lazy="no-proxy" on many-to-one element

Then it will work, thank you very much! In my situation, however I also need to find a way for it to work for polymorphic collections and the documentation on no-proxy says it cannot be used for collection-valued associations.

I am having the same problem. I have a polymophic many-to-one association that I am trying to lazy-load and an instance of the base class
is always loaded. I am using joined-subclass in the polymorphic class. Using lazy="false" and/or fetch="join" returns the correct subclass, but lazy="true" and lazy="no-proxy" do not. What's interesting is if I turn on debug level logging hibernate says thats its hydrated an instance of the correct class. Am I doing something wrong? Does anyone know if these same problems occur with lazy-loaded polymorphic collections?