Type specified for TypedQuery is incompatible with query return type [class java.lang.Double]

Question

I'am trying to make a join between two entities using j2ee and hibernate. But I get the following error:

java.lang.IllegalArgumentException: Type specified for TypedQuery is incompatible with query return type [class java.lang.Double]

This is the query that I'm trying to get work

Query query = entityManager
                .createQuery("SELECT avg(responseEnd - responseStart)  FROM QualiteDeService q  join q.test",QualiteDeService.class );

And these are the entities:

    @Entity
    public class QualiteDeService {

        private int id_qualite_service;
            private Test test;

        @Id    
        @GeneratedValue(strategy=GenerationType.IDENTITY)
        public int getId_qualite_service() {
            return id_qualite_service;
        }
        @ManyToOne
        @JoinColumn(name = "id_test", referencedColumnName = "id_test", insertable = false, updatable = false)
        public Test getTest() {
            return test;
        }
        public void setTest(Test test) {
            this.test = test;
        }
    }


    @Entity
    public class Test implements Serializable{
    private int id_test;
private int note;

    @Id    
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    public int getId_test() {
        return id_test;
    }
    public void setId_test(int id_test) {
        this.id_test = id_test;
    }
    }

Answer 1

The query return type need be compatible with the entity object in which you want to cast it. Update your code

entityManager.createQuery("SELECT avg(responseEnd - responseStart)  FROM QualiteDeService q  join q.test",Double.class );