hi all,

imagine you have A (many to many) B (one to many) C
B and C are lazy loaded
querying like this

will return a with b collection loaded but c not initialized, that is what we want.

But is there a way to force collection c to be loaded too, something like


i think "bs b left fetch join b.c" is incorrect.... because bs is a collection not an instance of B
I'm asking this because we are two in the forum needing this and that i'm not sure to understand the doc :


And is there an impact of the parameter max_fetch_depth on this ?


Thanks,
Anthony[/code]

No, you can't use "fetch" for collections twice in a single HQL query. Imagine what kind of join and result set would be produced. With your "fetch b, fetch c" query you'd get a product/cross join, which would retrieve a huge result set (really huge). Hibernate will then throw away most of the data (distinct style) to flatten this big result table. This is less performant than two selects, so we don't even provide this "feature" right now. That way, everyone will have good performance without thinking too much about the generated SQL.

The max_fetch_depth parameter has no influence on any collection roles or outer join fetching for collections, it is only relevant for single-ended associations (one-to-one, many-to-one).

ok thanks for reply,
the only thing is about
"less performant than two selects"

there won't be only 2 sql generated but 1(for a with b loaded) + 1 (to load c) per b = n+1 queries.

but the performance seems to be ok (i'm working on a test with 600 generated queries) it take 20 seconds to load a 3 level object graph , i was just thinking about how to generate only one sql, if we can't, we can't, no problem.


Thanks,
Anthony

Well, there are some usecases where it might make sense to outer join three (or four/five tables for many-to-many). I remember that there was a JIRA issue about that.

i took a look at jira, are you talking about this issue?
http://forum.hibernate.org/viewtopic.php?p=2197847

it's not the same problem isn't it?
Should i open a new issue?

No, there is an issue in JIRA that discusses the case of more than one "collection fetch".

argh, i've been searching for this issue for an hour, just can't get it i've made search on keyword "fetch" or "collection" but can't find.

Sorry to waste your time

Christian, this was a private discussion the team had.

too bad

Oh. Sorry :)

is there a way to be a virtual member of hibernate team? just to see this issue.... nop? ok no problem ;)

It's not really interesting. The conclusion was: "We don't want it right now, complexifies many other things as well, let's focus on things on TODO with higher priority".

Ok, anyway thanks a lot

That answers one of my earlier question.

Thanks to all
Shishir