excuse me, but i have a stupid question and i just can't remember...

is there a simple way to have the same function as "lazy loading" but for a to-one association.

I know that (simplifying)
outer-join = true will execute on query
outer-join = false will execute x queries

but i can't remember if it is possible not to join until we want it.

example
class A many - to - one class B

i want myA.B to be null until i call myA.getB() (that will generate SQL and hit the DB)


And excuse me again, it seems i'm too busy to remember some basics... :-/

Thanks

This is not possible (Keep something "null" until get is called.) You can use a proxy for the one side class though (take a look at http://www.hibernate.org/162.html it is conceptually the same as for a one-to-one)

thank you Michael, that's what i was thinking but i wanted to be sure

Anthony

I've been looking around the forum and experimenting to try to do the same thing.

I've got the lazy-loading with the proxy working great with many-to-one, but a one-to-one breaks if the -to-one object is null, as described at http://www.hibernate.org/Documentation/SomeExplanationsOnLazyLoading.

So I was wondering - has anyone come up with a good programmatic strategy for lazy-loading a one-to-one association that is not constrained (e.g. doing what Michael said is impossible: keeping the object null)?

Since you cannot proxy the -to-one class (B), seems like the only thing left to do is to remove the one-to-one relationship from the A mapping and then put some lazy-loading in the getB() method of the A class.

for example, in class A I have something like:



While I'm not thrilled about putting hibernate code into a property getter of my A class, it's what we did back in the JDBC days, and it's the only solution I've thought of. If anyone has better ideas I'd love to hear them.

Also, I was wondering if anyone knew the best way for A to get a reference to the session that loaded/locked it?

Or I suppose I could add a nullable B_ID column to TBL_A, map the association as a many-to-one with outer-join="false" and proxy B. Seems much less intrusive. Thoughts?

Is it made exactly on http://www.hibernate.org/Documentation/ ... azyLoading?

If no, can you give a piece of code?
Maybe you should had your complete example in a wiki page?
Or if you want just give the code, i'll complete the page.

Thanks
Anthony

Not sure I understand your question. The wiki page explains the problem very well, but doesn't offer any solutions for cases where the proxied object can be null. (Incidentally, I don't understand what that has to do with the "constrained" attribute -- that's my only question regarding the wiki page).

What I have found is that a many-to-one association doesn't have that limitation -- the proxied object can be null, because no extra join is needed -- the key of our -to-one class is stored in a nullable column of the table of our primary class.



Well I haven't tried to build the application-managed lazy loading stuff, but it's fairly straightforward. If I attempt it, I'll post the code and let you know how it turned out.

However, I am leaning towards the second strategy that I posted, which would be to make the relationship many-to-one, rather than one-to-one -- because the many-to-one association allows for the proxied class on the -to-one side to be null, whereas the one-to-one association does not.

If I refactor my tables & mappings as I described, I will let you know how it turns out and post some code.

I was just wondering if anyone else had encountered a similar problem and how they had dealt with it.

constrained="true" means that there is a foreign key constraint on the pk, and hence that the one-to-one association can not be null ... and therefore we can do lazy loading.

Gavin, but what about cascading saving as in http://forum.hibernate.org/viewtopic.php?t=932623 and http://forum.hibernate.org/viewtopic.php?t=932541
??