JPA, Entity manager, select many columns and get result list custom objects

Question

How I can get list of custom objects, like results below query:

SELECT p.category.id, count(p.id) FROM Product p left join p.category c WHERE p.seller.id=:id         


        

Answer 1

Using JPA 2.0 and EclipseLink impl

For the first question: list of custom objects(no table objects):

answer: create a custom model and use the @Entity and @Id

@Entity
public class QueryModelDTO implements Serializable{ 
    @Id
    private Integer categoryId;
    private int count;
    ---gets and sets
}

create the query and execute

QueryModelDTO qm = (QueryModelDTO) em.createQuery(
                "SELECT p.category.id as categoryId, count(p.id) as count FROM Product p
                left join p.category c WHERE p.seller.id=:id 
                GROUP BY c.id",QueryModelDTO.class)
                .setParameter("id", id).getSingleResult();

For the second: how to read the response on a map

answer: Use the QueryHints and ResultTypes (this is one variant for the @DannyMo answer)

Query q  = em.createNativeQuery("SELECT * FROM Foo f");
q.setHint(QueryHints.RESULT_TYPE, ResultType.Map);
List

I hope this helps