Get distinct values via hibernate

Question

I want to get distinct values by a parameter:

@Transactional
public List<data> getAllFromColumn(String identifier) {

    List<data> resultList = em.createQuery("SELECT DISTINCT p.market FROM data p", Data.class).getResultList();

    return resultList;
}

My problem is that this only returns me a NullPointerException. Any recommendations what is wrong, or what I can do differently?

I appreciate your answer!

@Jens EntityManager works fine. Have proved that by doing other easier queries. — Carol.Kar, Jul 23 '14 at 12:11
[http://stackoverflow.com/questions/300491/how-to-get-distinct-results-in-hibernate-with-joins-and-row-based-limiting-pagi] this may help you — subodh, Jul 23 '14 at 12:13
your code mixes `data` and `Data`. Maybe just a tipo, but I think it is worth fixing it. — SJuan76, Jul 23 '14 at 12:14
Is this the entire code snippet? From the snippet, only em being null can result into NPE, getResultList is guaranteed to never be null. Stacktrace would help here? — maress, Jul 23 '14 at 12:17
@maress Just checked it again! Yep thats the codesnipped. The thing is when loading hibernate with spring I get the NullPointerException. — Carol.Kar, Jul 23 '14 at 12:22

score 1 · Accepted Answer · answered Jul 23 '14 at 12:09

1

If HQL doesn't support select distinct (which it doesn't seem to according to the syntax), you can do this using group by:

SELECT p.market
FROM data p
GROUP BY p.market;

answered Jul 23 '14 at 12:09

Gordon Linoff

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Just read sth about a criteria builder. Any recommendations for putting that into the criteria builder? What is the syntax? I appreciate your reply! – Carol.Kar Jul 23 '14 at 12:10
1

@Vivien . . . My expertise is in SQL, not Hibernate. In this case, the query can be turned into an equivalent valid query using `group by`. – Gordon Linoff Jul 23 '14 at 12:16

Get distinct values via hibernate

1 Answers1