[hibernate-dev] Eager fetch and duplicates of collection elements

[Vlad Mihalcea]

Hi,

True. I also wondered why don't we use the DISTINCT as the default
mechanism.
While the underlying SQL would return a result-set according to the total
number of joined relations, we are building the entity tree hierarchy and
I don's see why a user would be interested in getting duplicate root entity
objetc references.

If I want to fetch the parent entity along with all its children, then I'd
rather expect to see distinct parent objects than an object reference for
each child entity.

Vlad

On Thu, Feb 11, 2016 at 3:48 PM, Gunnar Morling <gunnar at hibernate.org>
wrote:

> Hi,
>
> I understand that $subject is a known source of confusion for people
> when working with HQL/criteria queries and not applying something like
> DistinctRootEntityResultTransformer.
>
> I am seeing the same behaviour though when getting a root entity by id
> and join-fetching two (nested) collections. That's my model:
>
>     @Entity
>     public class Parent {
>
>         @Id @GeneratedValue
>         private Long id;
>
>         @OneToMany(cascade = CascadeType.ALL, fetch=FetchType.EAGER)
>         @JoinColumn(name = "parent_id")
>         private List<Child> children = new ArrayList<>();
>     }
>
>     @Entity
>     public class Child {
>
>         @Id @GeneratedValue
>         private Long id;
>
>         @ElementCollection(fetch=FetchType.EAGER)
>         @JoinTable(name = "Child_Properties")
>         @MapKeyColumn(name = "key")
>         @Column(name = "value")
>         private Map<String, String> properties = new HashMap<>();
>     }
>
> I am persisting a parent with one Child which has three "properties"
> entries. Loading the Parent by id yields three elements in the
> "children" list:
>
>     Parent loaded = session.get( Parent.class, 123 );
>     assert 1 == loaded.getConfigurations().size(); // <!-- Fails, it
> contains the same Child three times
>
> I don't think that's expected?
>
> I can file an issue, but first wanted to make sure I am not missing
> anything obvious.
>
> Thanks,
>
> --Gunnar
> _______________________________________________
> hibernate-dev mailing list
> hibernate-dev at lists.jboss.org
> https://lists.jboss.org/mailman/listinfo/hibernate-dev
>