[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-2480) Unify join fetch behavior for HQL and Criteria APIs

[wesley wu (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-2480?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_26960 ] 

wesley wu commented on HHH-2480:
--------------------------------

I need this improvement especially when I use EntityManager to do query rather than Criteria or HQL.

In fact, the HibernateEntityManager provides no way to force returning distinct top level pojo objects when there is an One-to-Many left outer join clause.

One of the workaround I learned from http://www.hibernate.org/117.html#A12 is to add a DISTINCT keyword after SELECT.

"Yes, in other cases an HQL distinct will translate straight into a SQL DISTINCT. Not in this case: you can not filter out duplicates at the SQL level, the very nature of a product/join forbids this - you want the duplicates or you don't get all the data you need."

But in two cases, this workaround failed to work:
1.  When the resultset should be paginated, I.E., setFirstResult() and setMaxResults() were used.
2.  When the resultset has LONGVAR field, like ntext, image in SQLServer. Database will generate a error like : ntext datatype could not be distinct compared."

And these two case should happen pretty frequently.

The conclusion : despite of using "setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY)" in Hibernate HQL queries and criteried queries, HibernateEntityManager has no way to eliminate the duplication of top level pojo objects when there is an One-to-Many left outer join clause.

We need this improvments indeed.

Thanks in advance.

> Unify join fetch behavior for HQL and Criteria APIs
> ---------------------------------------------------
>
>                 Key: HHH-2480
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-2480
>             Project: Hibernate3
>          Issue Type: Improvement
>          Components: query-criteria, query-hql
>    Affects Versions: antlr-rework
>            Reporter: Christian Bauer
>            Priority: Critical
>             Fix For: antlr-rework
>
>
> Can we consider changing the criteria API in 3.3 so that DISTINCT_ROOT_ENTITY is the default transformer?
> 10:28
> I remember that detecting "fetch" in HQL and applying this transformer is already on the list, right?
> 10:29
> or introduce config options for both APIs, so users can switch the default transformer
> 10:30
> also, verify this please: http://www.hibernate.org/117.html#A12
> Steve
> 2:31
> we should try to detect if any fetches are present
> 2:31
> otherwise DISTINCT_ROOT_ENTITY presents unecessary overhead
> 2:31
> i dont recall such a discussion regarding that  feature in HQL
> 2:32
> another option is sorta like i'm planning in other areas: fallback to subselect fetching

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