Eager loading in EntityQuery

[zaya]

I'm wondering if this is possible. I'm using EntityQuery in Seam Application Framework.

Say, I want to page query for Comment entity, but when I show comments for an article, I need the name of the user who contributed this comment, and this information is in my User entity.

The consequence is n+1 queries. How to avoid this?

[fhh]

Have you tried this?

SELECT c FROM Comment c
INNER JOIN FETCH c.user

Regards

Felix

[zaya]

It gave such error:

org.hibernate.QueryException: query specified join fetching, but the owner of the fetched association was not present in the select list

[zaya]

I read Hibernate doc, and it says:

Nor should fetch be used together with setMaxResults() or setFirstResult() as these operations are
based on the result rows, which usually contain duplicates for eager collection fetching, hence, the number of
rows is not what you'd expect.

EntityQuery used paging, there's certainly setMaxResults().

I'm kinda confused here. I executed generated mysql from mysql log, and the result seemed correct. Just the transaction was rolled back.

[zaya]

When I specify ejbql="select c from Comment c inner join fetch c.user" in components.xml, the generated ejbql is correct, but to retrieve the count number, it generated "select count(*) from Comment inner join fetch c.user where ......", that's wrong.

There isn't setCountEjbql() method either in EntityQuery or in Query. I have to extend the class. And because there is WHERE clause appended, I too have to recalculate the String, which is annoying and redundant.

Created Jira issue:
http://jira.jboss.com/jira/browse/JBSEAM-2177

And thanks fhh, I think you're correct.