Question

I’ve recently started using Hibernate and am trying to get my head around all the annotations and ensure I do things properly. I have two tables ‘user’ and ‘user_friends’ that are similar to the below

+------+------+-------+------+
| id   | name | email | etc. |
+------+------+-------+------+

and the user friends table

+--------+---------+----------+
| userid | buddyid | accepted |
+--------+---------+----------+

Now in SQL I ran a query that looked similar to

SELECT u.id AS id, u.name AS username, u.email AS email FROM user_friends 
INNER JOIN users AS u ON u.id = '1' WHERE buddyid = '2' AND ACCEPTED = 1 UNION ALL 
SELECT u.id as id, u.name AS username, u.email AS email FROM user_friends
INNER JOIN users AS u ON u.id = '2' WHERE buddyid = '1' AND ACCEPTED = 1;

I’ve got two classes in Java set-up in a fashion similar to this

@Entity
@Table(name="users")
public class User {

  @Id
  @GeneratedValue
  private int id;

  private int name;
  private int email;

  private DateTime registerDate;
  private DateTime lastActivity;

  private int currency;
  private int seasonCurrency;

  @OneToMany(fetch=UserBuddy.class, mappedBy="user", fetch=FetchType.LAZY)
  @JoinColumn(name="userid")
  @Filter(name="messengerBuddyFilter", condition="accepted=1")
  private Set<UserBuddy> _buddies;
}

@Entity
@Table(name="user_friends")
public class UserBuddy {

   private int id;
   private int name;
   private int email;
}

I asked this question before but still haven’t been able to get this working how I would like it. I need to be able to return a set of UserBuddy.class that contains the name and email of that Buddy and nothing else, not their register time etc (by using a User class to map). I’m also having difficulty ensuring it only returns buddies that have accepted the request (ACCEPTED=1)

Can anyone offer any suggestions?

Answer 1

You need to use native queries if you are using JPA (and named native queries with hibernate and JPA are problematic) or IIRC sql queries if just using pure hibernate.

This might work… just doing this quickly, use it as a place to start. Say you have an entity manager in JPA named em defined as a class member variable

@PersistenceContext(unitName = "MyPersistenceUnit_PU")
private EntityManager em;

…

some method…

List<UserBudy> buddyList = new <>ArrayList();
Query q = createNativeQuery("SELECT u.id AS id, u.name AS username, u.email AS email "
                          + "FROM user_friends "
                          + "INNER JOIN users AS u "
                          + "ON u.id = '1' "
                          + "WHERE buddyid = '2' "
                          + "AND ACCEPTED = 1 "
                          + "UNION ALL "
                          + "SELECT u.id as id, u.name AS username, u.email AS email "
                          + "FROM user_friends "
                          + "INNER JOIN users AS u "
                          + "ON u.id = '2' "
                          + "WHERE buddyid = '1' "
                          + "AND ACCEPTED = 1");
List<UserBudy> buddyList = (List<UserBudy>)em.getResultList);

This example is not a “named” native query. This is done inline similar to POJDBC (plain old jdbc). Like I said, if you were going to try to create a NamedNativeQuery using JPA and Hibernate you would get a “something or other not implemented yet exception”. Hibernate hasn’t supported named native queries with JPA forever. It is still in their bug tracker somewhere (for 5 or 6 years already) and it looks like they don’t give a rats ass about fixing it. Overall though, I’ve had less issues with Hibernate when working with PostgreSQL than with Eclipselink, so I can put up with it for now. 🙂

IIRC if you were to do this with pure hibernate you would create a Hibernate session object instead of an JPA EM object and use createSQLQuery instead. Other than that would be nearly the same.

i.e.

session.createSQLQuery("...");

If this didn’t help enough, you should now at least have enough info to figure it out.

And here is a link if you want to try what you are after using pure JPA. Look for the “line item summary” example about half way down this article.

http://www.oracle.com/technetwork/articles/vasiliev-jpql-087123.html

Remember when you are dealing with JPA you are joining the entities, not the tables. Anyway, that article is one of the clearest I’ve ever found showing how a lot of it works. Regards.