I have the following mapping:



I have a grandchild2 class which hibernate correctly persist it. When I try to search by using "find("from IParent"), it correctly instanciate grandchild2.

The problem is both Child1 and Child2 has same method called getB(). So after I cast the return object to IGrandChild2 then invoke the getB() method, it throws ClassCastException there.

It seems to be the proxy class CGLIBLazyInitializer's intercept call pass the proxy which contains 'IChild1' interface which grandchild2 doesn't not implement. Maybe it sees I used getB call then it will just radomly pickup the interface who has the method?

How can I ask hiberate choose IChild2 interface instead?

Thanks.

Furthur debugging showing:

AbstractEntityPersister has a list of all the subclasses interfaces regardless what conrete class should be.

createProxy method in that class will take all the interfaces regardless if any of them are not superinterface.

I had a feeling that Hibernate should do a second round filter to populate correct interfaces after it instantiated conrete class.

Maybe a Hibernate bug?

Looks like I am talking to myself here.:-(

Finally I get a chance to do furthur investigation around this problem.

Here is why, in getProxy code of CGLIBLazyInitializer,


When I use iterate() method to find this class, it only create an id and super-interface so it doesn't know all the subclass this particular id is implementing. So it passes every conceivable sub-interfaces to CGLib. So the proxy it returns contains all the interfaces regarless this id(instance) implemented or not. As I specified before, when invoking the method it could go to the wrong place.

Here is my hack to this problem since I don't think there is an esay way to re-narrow the interfaces after user get hold on this object's reference. Come think of it, it might be the IteratorImp's job to narrow the interface which should be doable.

Anyway, in intercept(....) method do the following will work:




Please remember this is my work-around right now since it defeats the purpose of using CGLib doing byte code enhacement.

This is all correct behavior for interface proxies. Try using concrete class proxies instead.

I wish I could but :-(

We are using code by contract(interface) everywhere (reference are all using interface).

I have been looking a little bit more, if I can break the lazy contract in the iterator.next() which I hit the db at that time then I can narrow down to the correct proxies, it might works a little bit better(cleaner) than my previous posted 'hack'.

What do you think, Gavin? I know you might say no...:-(

Hello,

I have exact the same problem that I posted recently.

Gavin wrote:


I do not agree with the opinion that this is the correct behaviour. I cannot even imagine that this bug is to stay in the Hibernate implementation.

Is it subject to change in the near future, or should I try the solution (work around) as supplied by no_ejb?

Or do you have better options?

Erwin

Hello,

Another workaround I use right now is to define the methods that for example exist in both IPerson and IOrganisation in one super-interface, like IEmailable. Multiple inheritance is possible for interfaces and both are being derived from the IEmailable interface. The casting problem disappears, because the class will be casted to the unified IEmailable interface.

Greetings,
Erwin

Hi,
I've got the same problem. Has something changed since April? It seems to me more like a bug then a correct behavior. I thought I should use interface proxies for polymorphism, but this "bug" or "behavior" kills interface polymorphism.

What do you thin Gavin? How to use subclasses and proxies together?
Btw.: My ClassCastException is thrown when calling equals() or getId().

Thanks
Pavel

We have definitely found that using the Interface style of lazy loading to be buggy when combined with inheritance mappings. We get intermittent errors when doing loads on base classes - occasionally the returned class is of the wrong type, resulting in a class cast exception when invoking a method on the subclass.

The following code seemed to work in getting consistent results however we are ripping out a lot of the inheritance stuff because it's causing too many headaches.

if(templateBasePrintHDO instanceof HibernateProxy){
HibernateProxy proxy = (HibernateProxy) templateBasePrintHDO;
LazyInitializer lz = HibernateProxyHelper.getLazyInitializer(proxy);
TemplateBasePrintHDO tbph = (TemplateBasePrintHDO)lz.getImplementation();
Hibernate.initialize(tbph.getPreviewImage());
}

The documentation could definetly be improved in this area - a guide on how to properly implement interface proxies with inheritance would be very useful. For example, things like whether the subclass interfaces need to implement the base interfaces etc