[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-2477) lazy fetching ManyToOne produces inproper proxies when using single table inheritance strategy

[Tun Schlechter (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2477?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_29907 ] 

Tun Schlechter commented on HHH-2477:
-------------------------------------

Unfortunately, this hack only enables you to know the real classname, you still cannot cast the object...

Finding the exact class works as well with the dynamic class.isInstance(object) - Test, even if instanceof operator test fails... 
>From this, one might expect that "dynamic" class.cast(object) casting works even if (class) object casting does not, but unfortunately, it does not.

Maybe working around toplink limitations is easier, we will see...


> 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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