[hibernate-dev] Proxies and typing

[Sanne Grinovero]

Would it be acceptable for such a use case to demand to use the
interface instead ?

UserImpl u = (UserImpl) session.load( UserImpl.class, ... ) -> Illegal
type exception
User u = (User) session.load( User.class, ... ) -> Ok

I think it would, as the first case would work only in certain
situations even with the current code, depending if you actually get a
proxy or not, so I would consider such code wrong even with the older
API.

It would only break this currently working code:
User u = (User) session.load( UserImpl.class, ... )

but it won't break at runtime, it would stop compiling.. which is a
good warning imho. Existing code (already compiled) would throw a
runtime exception though.

-- Sanne


On 25 January 2012 21:26, Steve Ebersole <steve at hibernate.org> wrote:
> BTW, I did go back and verify that indeed the mismatch  is with
> @Proxy.proxyClass specifying an interface.  Consider an example:
>
> @Entity
> @Proxy(proxyClass=User.class)
> public class UserImpl implements User {
>    ...
> }
>
> You will never be able to cast proxies instance of this thing to
> UserImpl.  This call will fail with CCE:
>
> UserImpl u = (UserImpl) session.load( UserImpl.class, ... )
>
> get() may or may not work depending.
>
> This is the source of us not being able to offer generic signatures.
>
>
> On Wed 25 Jan 2012 01:33:14 PM CST, Steve Ebersole wrote:
>> In regards to the new "load access", a user asked why we don't
>> leverage generics.
>>
>> The problem is the existence of @Proxy#proxyClass. We have the same
>> issue with Session#load/get taking the entity Class. We can't use a
>> generic sig like:
>>
>> public <T> T load(Class<T> entityType, ...)
>>
>> because at times we return objects that are not typed to <T>. I have
>> to dive back into the specifics, but IIRC the problem is that we don't
>> do the expected thing and have the generated proxy class extend from
>> the entity class if @Proxy#proxyClass names an interface. I remember
>> this change way back when, but the specifics of why escape me at the
>> moment.
>>
>> IMO I think providing generic signatures would obviously be a great
>> improvement. Is it enough to change this behavior?
>>
>> WDYT?
>>
>
> --
> steve at hibernate.org
> http://hibernate.org
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