[hibernate-dev] Fwd: Re: Proxies and typing

[Steve Ebersole]

Oops, forgot the name of the test package I referred to :)

org.hibernate.test.dynamicentity

On Wed 21 Mar 2012 08:06:44 AM CDT, Steve Ebersole wrote:
> Comments inline...
>
>
> On Wed 21 Mar 2012 05:36:01 AM CDT, Sanne Grinovero wrote:
>> As an API user if I'm expected to use the _User_ interface, I think I
>> would expect the annotations to be defined on the interface, not on
>> the UserImpl.class .. as with the rest of mapping annotations.
>>
>> I don't know about the technical requirements to make this
>> implementable; I guess you need some UserImpl class as a prototype?
>>
>> If so wouldn't it make sense to have
>>
>> @Entity @PrototypedBy(UserImpl.class)
>> public interface User {
>>
>> @Id Long getUserId();
>> void setUserId(Long id);
>>
>> }
>>
>> public class UserImpl implements User {
>> ...
>> }
>
> I'm ok with this. I do not like the phrase "prototyped by", but the 
> general idea is good. In fact this was my proposal initially on how to 
> map this situation :)
>
> However, I want to at least allow both ways to map it. Couple of 
> reasons. First (brought up on the JPA list in regards to this 
> proposal) is that you now have a bi-directional relationship between 
> the interface and implementation. Why is that important? The reasoning 
> on the JPA list was just the unnaturalness of the bi-directionality 
> and being able to split each into jars (thinking osgi). Another 
> thought I had was imagine you are trying to persist interfaces 
> provided to you by another group/project.
>
>
>> And ideally I would expect the "prototype" class to be not needed / 
>> optional.
>
> Yes we spoke of this before also. I agree the interface should be 
> enough. And as I pointed out to you, nothing in Hibernate internals 
> disallows this. We have quite a few tests (see the ... test package) 
> making sure that persisting interfaces works using proxies and various 
> approaches. But here is rub... If Hibernate is the one generating the 
> proxies, how is the application supposed to instantiate instances of 
> the entity? I don't have a clean answer to that at the moment.
>
>
>> Finally, since I'd expect the setter / getter implementations in the
>> proxy to be generated by us, could we have them take care of
>> bi-directional relations, to update both sides of relation
>> automatically and correctly? I was speaking recently to a Ruby
>> developer who just switched to JavaEE, and he pointed out that this
>> requirement is long gone in other persistence APIs.
>> I know by experience this also frequently bites beginners, and even
>> experienced developers have to write code about this.. this looks like
>> a chance to evolve?
>
> You don't need proxies to do this. In fact unless things have changed 
> drastically, most other providers actually use bytecode manip (build 
> time or via agent) rather than proxying. Ideally, if we are going to 
> offer this "evolution", I'd prefer that it be more consistent, meaning 
> that it would be nice if it was not only available to those mapping 
> interfaces. We do have a long-standing task to investigate java agents 
> for in-VM enhancement, though a major pre-req there is actually 
> getting some decent enhancement code. Our current enhancement code is 
> pretty lacking.
>

-- 
steve at hibernate.org
http://hibernate.org