How to use the Distinct interface with Criteria queries

JamieV · **Joined:** Mon Feb 11, 2008 9:23 am **Posts:** 2

Hi,

I have an Email object, which has a list of Recipient objects and I would like to know how to use criteria queries to match the e-mail address of one of the recipients without getting back duplicate objects.

I have searched around a lot and found the Distinct interface (org.hibernate.criterion.Distinct) which I believe was added in Hibernate 3.0.2 to remedy situations like this, but I cannot figure out how to use it. I can't find any examples of use of this class online.

Please could somebody let me know how to use this Distinct interface for use with the following simple code:

Code:

Criteria crit = this.getSession().createCriteria(Email.class);
Criteria recipCrit = crit.createCriteria("recipients");
recipCrit.add(Restrictions.eq("emailAddress", "email@address.com"));

I cannot use the following line because I plan to page the results:

Code:

crit.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);

Thanks in advance.

kuzhali · **Posted:** Thu Mar 13, 2008 4:14 am

If you want to fetch the distinct value of only one field, then you can go for this

recipCrit.setProjection(Projections.distinct("propertyName"));

JamieV · **Joined:** Mon Feb 11, 2008 9:23 am **Posts:** 2

Thanks for the advice, kuzhali. I did fiddle around with something similar to what you suggested at the time, but in the end I settled for changing it to an HQL query. This actually turned out better because I could use the distinct keyword (similar to SQL)...

Code:

String hql = "select distinct..."

and I could also just select the fields I needed from the query instead of the whole object which made everything slightly quicker.