Re: [Hibernate-devel] Help with One-to-Many

[Paul S. <pau...@ne...>]

Okay, I think we're (almost?) on the same page. I'm *not* advocating a 
heavy framework that does a whole bunch of magic for you, like 
maintaining integrity of bidirectional associations.

Where a bidirectional association exists simply tweak the relational 
mapping. For example to avoid "doubling up" on foreign keys to provide 
visibility from both ends as is done now in a one-to-many.

This gives the possibility of integrity checking, which in my experience 
is very useful once the database gets large and/or complex.

No extra API should be needed - it's still non-intrusive.

Hibernate shouldn't manage the integrity of the association - the 
programmer still has to ensure both ends match. The code should be no 
different if the class is being persisted or not, at least in this respect.

PaulS.

Gavin_King/Cirrus%CI...@ci... wrote:
>>Your statement about such a concept being alien to idiomatic Java to me
>>seems to be putting the horse before the cart. While true, I think that
>>it loses sight of what we're building - for me at least that's the
>>object model.
>>
> 
> Hmmmmmmm. Perhaps. I was very keen to stay with the current approach of
> just adding persistence to Java, not trying to add any extra semantics, not
> trying to build an application framework. If you manage to convince me that
> its possible to do bidirectional associations with no xtra API then I'm
> sold on it.
> 
> 
>>There are ways to do this, and all the commercial O/R tools that I've
>>used support this. Basically the association is "managed" from one end
>>when it comes to persisting the association - and it's straightforward
>>to tell when things are screwy.
>>
> 
> Interesting. The thing I've used that does bi-directional associations -
> namely Visual Age for Java's EJB associations - uses a generated class that
> ensures association integrity from _both_ ends. Its arguably not a good
> design and is not consistent with the approach in this project. (I think
> they have a more difficult problem though, because the ends of the
> association might be remote.)
> 
> 
>>I don't see the problem. Your code (i.e. not Hibernate, the users code)
>>is still responsible for making sure  all the persistent objects point
>>to the right places. This is true without persistence, and I wouldn't
>>expect the persistence layer to do this for you - that would be intrusive.
>>
> (snip)
> 
>>Yep - and that's fine. And if you wanted to you *could* do a consistency
>>check quite transparently. There's actually huge advantages in being
>>able to do that.
>>
> 
> Yeah, I was thinking about this on the way home, after firing off that last
> email and thinking "Well, you could just let the users manage integrity
> themselves, but validate the state before we persist anything" ... All we
> would need to implement this approach is some code to validate the
> association somewhere. There wouldn't need to be any other changes to the
> runtime engine and there wouldn't need to be any API. This would make me
> happy.
> 
> I've been thinking of one-to-many associations while I've been writing
> this, but I think much the same thing goes for many-to-manys (where its a
> collection on each end - mapped to the one table).