Efective loading of more one-to-many mapped properties

jarda · **Joined:** Thu Oct 21, 2004 9:12 am **Posts:** 1

Hibernate version: 2.1.5

I inherited one ugly project of my colegue and I found it is realy far from 'efective'. I have tried to read about Hibernate in manual and make it better, but still don't know if I have the best possible solution or not..

I have class X with more array/list properties a, b, c .. mapped as one-to-many. I need to load all (or some interval) of Xs from database. The question is, how many queries Hibernate needs to do?

With one property I can use join fetch, but on second, third ... it does not help.

Next thing I have tried was to set batch-size on properties, it helps but works just with lists and it leads to n/batchsize queries minimaly.

Is there another way to solve this problem? Loading of such objects should be optimizable to one query for instances of X and one query for each property. So I don't know if Hibernate doesn't support it or I just have a bad mapping or something else..

anthony · **Posted:** Thu Oct 21, 2004 11:52 am

1- open session
2- select a from a left fetch join a.bs
3- select a from a left fetch join a.cs
4- select a from a left fetch join a.ds

you'll have 3 queries that is better than 3*n

adcworks · **Joined:** Fri Jun 18, 2004 10:17 am **Posts:** 140

i've just had to do the same thing but it appears anthony's answers is loading the main class A each time??

well, sorry if i got that wrong (totally possible), but I decided to load my main class with 1 fetch and then to load the other collection directly.

Code:

Query q = session.createQuery(
                "from X as x " +
                "   left outer join fetch x.coll1 " +
                "where x.id = :xId"
            );
            q.setParameter("xId", idParam);
            
            X x  = (X) q.list().get(0);
               
            q = session.createQuery(
                  "from CollType as c " +
                    "where c.x.id = :xId"
            );
            
            q.setParameter("xId", idParam);
            
            x.setCollType(q.list());

this works but i don't know if it's the best way. It just seemed to me that select from a with a fetch for B, C and D was heavy in comparison??