[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-879) Enable joining the same association twice with Criteria

[Ashkan Aryan (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-879?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=39793#action_39793 ] 

Ashkan Aryan commented on HHH-879:
----------------------------------

With regards to Simon's suggestion above, it does work, however there are a couple of issues you need to take into account while implementing it. Here's an example of how I did it. 

relationship : ClassA- 1 : 0...* -ClassB

Assuming that you already have a criteria for ClassA, called classACriteria, you will need to add something like this to it:

{code:title=sample|borderStyle=solid}
             
                Conjunction conjunction = Restrictions.conjunction();

                DetachedCriteria detachedCriteria1 = DetachedCriteria.forClass(ClassA.class).setProjection(Projections.id());
                detachedCriteria1.createAlias("classB", "classBAlias1"); //classB is the name of property representing a bag of ClassA instances in ClassB
                detachedCriteria1.add(Restrictions.eq("classBAlias1.field1", value1)); //Replace field one with the appropriate property name
                detachedCriteria1.add(Restrictions.eq("classBAlias1.field2", value2)); //

                DetachedCriteria detachedCriteria2 = DetachedCriteria.forClass(ClassA.class).setProjection(Projections.id());
                detachedCriteria2.createAlias("classB", "classBAlias2"); 
                detachedCriteria2.add(Restrictions.eq("classBAlias2.field3", value3)); 
                detachedCriteria2.add(Restrictions.eq("classBAlias2.field4", value4)); 

                conjunction.add(Property.forName("id").in(detachedCriteria1)); 
                conjunction.add(Property.forName("id").in(detachedCriteria2)); 

                classACriteria.add(conjunction);

{code}

Please note, you'll have to specifically set the projection on each criteria (in this case we're assuming that ClassB has a unique identifier) otherwise you'll get a nasty NPE.

As mentioned before this is not ideal (a proper join would've been preferable in terms of performance) but at least it works!










> Enable joining the same association twice with Criteria
> -------------------------------------------------------
>
>                 Key: HHH-879
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-879
>             Project: Hibernate Core
>          Issue Type: Improvement
>          Components: core
>            Reporter: Vladimir Bayanov
>
> Make double joining the same association with Criteria.createCriteria possible. See: http://forum.hibernate.org/viewtopic.php?t=931249

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