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JasDA
 Post subject: "Reverse" a join with the Criteria API
PostPosted: Tue Mar 28, 2006 4:54 am 
Newbie

Joined: Wed Nov 02, 2005 6:07 am
Posts: 12
Hibernate version: 3.xx

Hi,

I've got table A and table B. In most cases I process a join between these tables to get the information I need.

Code:
Criteria crit = sess.createCriteria(CustomerAddress.class)
            .setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY)

           crit.createAlias("B", "B");

......

With this I get every entry of table A which has an entry in table B. But now I've got an understanding problem. How is it possible to get every entry in table A which has NO entry in table B?
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tenwit
 Post subject:
PostPosted: Wed Mar 29, 2006 12:48 am 
Expert
Expert

Joined: Thu Dec 23, 2004 9:08 pm
Posts: 2008
Assuming that B is a set, map or similar, then you want something like this:
Code:
Criteria crit = sess.createCriteria(A.class);
crit.setProjection(Projections.alias(Projections.count("B"), "count"));
crit.add(Restrictions.eq("count", 0));
You could also use subqueries, but this is the most efficient.
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