Hello,

Is there a way to apply a limit on the child collection mapping?

For example, I have Department and Employees as below


What can I do so that I only get top 5 employees from the department?

I looked into using Filter, but couldn't figure out how to limit without using subselect, and MySQL doesn't support limit on subselects.

Thanks!
jydev

If you can't express the condition with @Where then chances are custom loaders are your last chance.



Farzad-

Farzad,
Thanks for your reply. I am trying to use the custom loader, but having issues.

I am getting "Named SQL query not known" error. When I stepped through the Hibernate source, for some reason it is calling getNamedSQLQuery(), rather than getNamedQuery(). I tried to track down how to trigger it to call getNamedQuery(), but the source path branches way before these calls are made and was a difficult to track down.

Here is my annotated sample:



What am I doing wrong? Note that if I swith over to NamedNativeQuery, it works.

Using Hibernate 3.2.5 and HibernateAnnotations 3.3.0
Thanks,
jydev

That's actually a valid point but as far as I know custom loaders work with native queries so you won't have a choice here.



Farzad-


ps. I might be totally wrong so let me know if you find a way around it.

Thanks for the quick reply.

I lied about everything working ok with native query. I don't get hibernate exceptions, however my collection (topEmployees) is null.

I traced the code and when Hibernate retrieves the results set, there are results. But eventually, the call ends up at the following, which doesn't return anything (return type of void).


So where and how is the results from the query being mapped to the parent (in this example Department).

Thanks again,
jydev

That means hibernate does not know it is a collection loader. In the xml mapping way there is a tag that specifies this. I don't know what the equivalent annotation is, but I will look and tell you if I find anything.



Farzad-

Take a look at this one. it might help.

http://forum.hibernate.org/viewtopic.php?t=982986



Farzad-

Thanks. I finally got it working using sql-query in mapping file.
It's weird. The documentation seems to indicated it supports @NamedQuery (hql), but the code always looks calls getNamedSQLQuery(). I also tried defining hql named query (using query tag instead of sql-query) in the mapping file and the same thing happens... Oh well. I think my query was more efficient using SQL, so it worked out. However, it would have been nice to define this using annotation. I couldn't find annotation equivalent for load-collection.

Anyway, thanks a lot for your help!

There doesn't seem to be any. If I recall correctly everywhere I looked it is said to just put the @Loader and it flies. However, in my case I get NPEs due to uninitialized collections. I would like to look at this to find out what's wrong but I might not be able to do it very soon. In any events, it's good you solved your problem.


Farzad-