JPA: Query that returns multiple entities

I'm writing a JPQL query that joins across three tables. In my resultlist I would like to get all three entities per matching row (hope that makes sense).

Any ideas?

Hibernate 3.x is my JPA provider.开发者_如何学JAVA

IIRC, you can do a SELECT o1, o2, o3 FROM EntityA o1, EntityB o2, EntityC o3 WHERE ...., and the result will be a List<Object[3]>, where the array contents will contain the o1,o2,o3 values.

This is a Spring Data sample, however its works the same way in JPA

//HQL query
 @Query("SELECT c,l,p,u FROM  Course c, Lesson l, Progress p, User u "
            + "WHERE c.id=l.courseId AND l.id = p.lessonId AND p.userId = u.id AND u.id=:userId AND c.id=:courseId")
    public List<Object[]> getLessonsWithProgress(@Param("userId") Integer userId, @Param("courseId")Integer courseId);

Then, I call this method and print the results:

List<Object[]> lst = courseRepository.getLessonsWithProgress(userId, courseId);
for (Object o[] : lst) {
    Course c = (Course) o[0];
    Lesson l = (Lesson) o[1];
    Progress p = (Progress) o[2];
    User u = (User) o[3];
    //all the classes: Course, Lesson, Progress and User have the toString() overridden with the database ID;    
    System.out.printf("\nUser: %s \n Lesson: %s \n Progress: %s \n Course: %s",u,l,p,c);
}

The output @Test is here:

User: com.cassio.dao.model.User[ id=1965 ] 
Lesson: com.cassio.dao.model.Lesson[ id=109 ] 
Progress: com.cassio.dao.model.Progress[ id=10652 ] 
Course: com.cassio.dao.model.Course[ id=30 ]

Cheers

Since You are asking JPA: Query that returns multiple entities, EclipseLink too comes under it. And I reached on this question googling for EclipseLink. So here is my solution. Hope it works for you.

TypedQuery<Object[]> query = entityManager.createQuery("select p from Post p where   p.publisher.pubId= :ID order by p.createdAt desc",
                Object[].class);
query.setParameter("ID", publisherID);

Then you can loop through the result objects and cast them accordingly.

for (Object result : query.getResultList()) {
            myList.add((Post) result);
        }

You can also try this,

Query query = entityManager.createQuery("select p from Post p where   p.publisher.pubId= :ID order by p.createdAt desc");

Reference:http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Querying/JPQL

In case of many to one or one to many relationship how to get multiple records of one of the entities? lets say A is one entity and B is another entity but they have one to many relationship and when you get result you expect B has one record and A has more than 1 record? My query is as below but I don't know how shall I get multiple records of 2nd entity?

@Query("SELECT wl, gr FROM WatchList as wl, GeozoneReference gr " +
            "WHERE wl.watchlistId = gr.objWatchList.watchlistId " +
            "AND wl.watchlistId =:watchlistId")
    List<Object[]> findWatchlistByWatchlistId(@Param("watchlistId") Long watchlistId);