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http://opensource.atlassian.com/projects/hibernate/browse/HHH-2477?page=c...
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Chris Lowe commented on HHH-2477:
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Chris, thanks for the prompt response.
I accept your workarounds are valid for a pure Hibernate environments, but as a pure EJB3
environment this isn't this still an issue?
Like Sebastian Kirsch comments above, I'm getting this issue with a JOINED
inheritance. Before adding a lazy association my EJBQL was returning a subclass as
expected. After adding the lazy association I now get the root superclass. This
behaviour was not expected. I've even gone as far specifying my query in terms of the
expected subclass, but I still get the root superclass - so how can I even get to my
subclass at all?! What's more, the lazy associations that I have specified are not
even directly against any of the classes in the inheritance structure - they're on the
One side of a ManyToOne. The Many side is on the entities in the inheritance structure,
but aren't the Hibernate implementations of the various collections supposed to
prevent the need for proxying the parent class?
So with respect to Hibernate being the provider to an EJB3 implementation, is this still
an issue? Or is this something that needs to be taken up elsewhere?
I feel like I'm faced with something that essentially makes essentially makes entity
Inheritance and FetchStrategy.LAZY mutually exclusive and that just seems wrong. There
was nothing to hint at this problem in the Hibernate EJB3 docs (or even after scanning
through the EJB3 spec for that matter).
Best regards,
Chris.
lazy fetching ManyToOne produces inproper proxies when using single
table inheritance strategy
----------------------------------------------------------------------------------------------
Key: HHH-2477
URL:
http://opensource.atlassian.com/projects/hibernate/browse/HHH-2477
Project: Hibernate3
Issue Type: Bug
Components: core
Affects Versions: 3.2.1
Environment: hibernate 3.2.1-GA, postgresql 8.1
Reporter: Daniel Nguyen
Attachments: bug.zip
Original Estimate: 1 hour
Remaining Estimate: 1 hour
I have entity base class Vehicle and entity class Car which extends Vehicle (using single
table inheritance strategy).
I also have entity class User which have single-ended @ManyToOne relation from User to
Vehicle with lazy fetching.
Now there is a Car instance "c" and User instance "u" with relation
to "c". Lazily fetching vehicle from "u" results with proxy object
"o" which is instanceof Vehicle but not instanceof Car as expected. So it's
impossible cast "o" to Car or at least read any of Car's property from
"o".
This is serious problem when inheritance is extensively used because inproper proxy
object remains in cache. To walkaround I'd have to resign with lazy fetching (much
performance loss) or manually replace proxy object in cache.
testing code:
SessionFactory sf = null;
Session s = null;
Transaction tx = null;
try
{
sf = cfg.buildSessionFactory();
s = sf.openSession();
tx = s.beginTransaction();
//create car
Car car = new Car();
car.setIdVehicle(1);
car.setAge(5);
s.save(car);
//create user of car
User user = new User();
user.setIdUser(1);
user.setVehicle(car);
s.save(user);
//make sure it is actually added
s.flush();
// test 1 - works ok, because we loaded vehicle before user
s.clear(); //clear cache
Vehicle vv = (Vehicle)s.get(Vehicle.class, 1);
User uu = (User)s.get(User.class, 1);
//we know that user vehicle is actually a Car
Car cc = (Car)uu.getVehicle();
// test 2 - fails, when using lazy fetching
s.clear(); //clear cache
User u = (User)s.get(User.class, 1);
Vehicle v = u.getVehicle();
//we know that user vehicle is actually a Car
//so we cast to Car but ClassCastException is raised!!!
Car c = (Car)v;
//let's check what's actual class of v
System.out.println(v.getClass().getName());
System.out.println(v.getClass().getSuperclass().getName());
//result:
// test.hibernate.Vehicle$$EnhancerByCGLIB$$12ce1883
// test.hibernate.Vehicle
//but I expected:
// test.hibernate.Car$$EnhancerByCGLIB$$xxxxx
// test.hibernate.Car
}
finally
{
if (tx!=null)
tx.rollback();
if (s!=null)
s.close();
if (sf!=null)
sf.close();
}
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