OneToMany fetchType EAGER produces duplicate results

cwhite102 · **Joined:** Sun May 15, 2005 12:01 am **Posts:** 8

Hibernate version:

hibernate-3.1rc2
hibernate-annotations-3.1beta6

I seem to get different results with LAZY vs. EAGER fetching on this relationship. The two entities involved are Group and Resource with a bidirectonal OneToMany / ManyToOne

Here's the relevant beans / annotations

Code:

public class ResourceBean {
...
    @ManyToOne( fetch=FetchType.EAGER )
    private GroupBean group;
}

public class GroupBean {
...
    @OneToMany( mappedBy="group", fetch=***FetchType.EAGER***)
    private Set<ResourceBean> resources = new HashSet<ResourceBean>();
}

If the highlighted fetchType is EAGER, and I do a 'findAll' on Group, I get duplicate entries from the Resources join. If the fetch type is LAZY, the results are as I'd expect (one object per Group).

I'm using the code patterns in CaveatEmptor demo, so the findall is....

Code:

   public List<T> findAll() {
        return findByCriteria();
    }
    protected List<T> findByCriteria(Criterion... criterion) {
        Criteria crit = getSession().createCriteria(getPersistentClass());
        for (Criterion c : criterion) {
            crit.add(c);
        }
        return crit.list();
    }

The Eager SQL is basically...

Code:

select * from groups this_ 
left outer join resources resources3_ on this_.groupId=resources3_.group_groupId

Am I doing something wrong or is this a bug? Is it my responsibility to somehow unique in the findByCriteria? (eg. I've seen posts about putting results in a Set to remove duplicates). Just doesn't seem right to have to do that here, so I figured I'd post...

emmanuel · **Posted:** Wed Nov 09, 2005 7:43 am

you're using java.util.List with no indexed column so it is considered a bag hence fetching 2 collections including a bag is not possible in hibernate

bjoben · **Joined:** Tue Dec 13, 2005 9:13 am **Posts:** 4

I have the same problem when i eagerly fetch an object with, in this case, a couple of List-collections. And while I understand why this happens with an outer join i tried with setting the FetchMode to FetchMode.SELECT in a query
and it correctly fetches the correct number of beans in the collection.
However, I have a generic dao, and to set this on the load operation for every possible bean and its collections is not feasible.
I'd thought i'd set the fetchmode in the mapping file but since i use annotations i'd like to annotate the bean. But i can't find a way to do that.
Please make it possible!
I'll go down another path till then :-)
/björn

emmanuel · **Posted:** Tue Dec 13, 2005 12:16 pm

this is already possible use fetch=FetchType.LAZY on you associations

bjoben · **Joined:** Tue Dec 13, 2005 9:13 am **Posts:** 4

oh i thought i could fetch eagerly with select fetchmode.
i didnt know that setting fetchmode.select implicitly made my fetch lazy.
i used a Set object instead of List though.

damonf · **Joined:** Wed Dec 21, 2005 6:57 pm **Posts:** 70

Emmanuel, I think you mis-read his post. The findAll method returns a list, but the mapping is a Set, not a List. His mappings have no bags.

Can you clarify why you say it is a problem with bags?

emmanuel · **Posted:** Sat Mar 08, 2008 1:15 pm

ah, to the original problem, the query needs to use a DistinctRootEntityResultTransformer