Yo! - object graph loading!

kedaar · **Posted:** Mon May 31, 2004 10:33 am

Hi,

Ive read a couple of posts but Im still confused.

If I have tables A->B->C (A has a set of Bs, B has a set of Cs). With UseOuterJoin=false and lazyLoading=true.

Ive tried the query:
"from A as a
left join fetch a.B as b
left join fetch b.C"

It doesnt throw an exception but returns A's with no B's attached.

I recall reading that you can only have one left join fetch in your query. I also read other people suggesting the above query (which has two fetches). Its also quite possible that my settings are screwed.

So to recap my question is how can I get an object graph of A's with B's and C's attached.

egervari · **Joined:** Sun Oct 26, 2003 5:05 am **Posts:** 139

I'd normally just have a set of B's defined on A and a set of C's defined in B in the hibernate mapping file. Then with lazy-loading set to true, when I load A, I can just eagerly get b's and c's (so if you only want A, you don't have to waste time getting the B's and C's. You usually end up doing something like

a.getBs().size();

and for loading all the b's and c's, you do

Code:

Iterator i = a.getBs().iterator();
while( i.hasNext() ) {
    B b = (B) i.next();
    b.getCs().size();
}

That's all I do anyway.

kedaar · **Posted:** Mon May 31, 2004 1:33 pm

Well Im using the dto's on the client side after the session is closed. I think the pattern is called thread local session.

I need to load the 1-to-many's explicitly in a query.

anthony · **Posted:** Mon May 31, 2004 2:02 pm

you can't, only one collection can be fetch in a query

kedaar · **Posted:** Mon May 31, 2004 3:23 pm

Thank you.

It seems like a strange limitation - is there plans to allow this in future versions?

anthony · **Posted:** Mon May 31, 2004 5:43 pm

hi kedaar,
not as strange as you think, of course this feature would "seem" powerfull.
But you only have to think of the consequence: a cartesian product on the resultset Hibernate core need to analyse to fill your object graph.

Don't worry;)