unexpected JPA results

Question

Hi, Im learning JPA and having problems. My main problem is when i join my entitys and dont quite understand why im getting the results i am .. and its realy slowing my progress if someone could help i would be very greatful.

Entitys

College

@Entity
@NamedQueries({
    @NamedQuery(name=College.allCollegeQuery,query="SELECT col FROM College col"),
    @NamedQuery(name=College.collegeStudentJoinQuery,query="SELECT DISTINCT col FROM College col JOIN FETCH col.students"),
    @NamedQuery(name=College.collegeStudentBasicJoinQuery,query="SELECT col FROM College col JOIN col.students s")
})
public class College {

    public static final String allCollegeQuery = "allCollegeQuery";
    public static final String collegeStudentJoinQuery = "collegeStudentJoinQuery";
    public static final String collegeStudentBasicJoinQuery = "collegeStudentBasicJoinQuery";

    @Id
    @GeneratedValue
    private long id;
    private String name;

    @OneToMany(mappedBy="college")
    private List<Student> students;

    public long getId() {
        return id;
    }
    public void setId(long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    public List<Student> getStudents() {
        return students;
    }
}

Student

@Entity
@NamedQueries({
    @NamedQuery(name=Student.allStudentsQuery, query="SELECT stu FROM Student stu"),
    @NamedQuery(name=Student.studentsCollageQuery, query="SELECT stu.college FROM Student stu WHERE stu.id = :id"),
    @NamedQuery(name=Student.studentsWithCollageIDQuery, query="SELECT stu FROM Student stu WHERE stu.college.id = :id")
})
public class Student {

    public static final String allStudentsQuery = "allStudentsquery";
    public static final String studentsCollageQuery = "studentsCollageQuery";
    public static final String studentsWithCollageIDQuery = "studentsCollagewithIDQuery";

    @Id
    @GeneratedValue
    private long id;
    private String name;

    @ManyToOne
    private College college;

    public long getId() {
        return id;
    }
    public void setId(long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    public College getCollege() {
        return college;
    }
    @XmlTransient
        public void setCollege(College college) {
            this.college = college;
        }
    }

Ok so my goal is to query all college's and to return all the students related to them. Which i was expecting my named query to do

SELECT col FROM College col JOIN col.students s

My responce was (invoked via glassfish Tester interface)

    <return>
        <id>1</id>
        <name>"Bournemouth</name>
    </return>
    <return>
        <id>1</id>
        <name>"Bournemouth</name>
    </return>
    <return>
        <id>1</id>
        <name>"Bournemouth</name>
    </return>
    <return>
        <id>1</id>
        <name>"Bournemouth</name>
    </return>

As you can imagen this college only exists once in the database, but i know there are four students attached to this college entity (which i guess why it has repeated). The solution i and kind of hoping for would be somthing like (in a sudo xml kind way)

<return>
   <id>1</id>
   <name>Bournemouth</name>
   <students>
     <student>
     </student>
    </students>
</return>

any help tips or pointers would be greatfuly recived Thanks

--------------------------- Additional Info ------------------------------

So i performed the SQL logging as Pascal kindly suggested which upon calling the method genorates

SELECT DISTINCT t1.ID, t1.NAME, t0.ID, t0.NAME, t0.college_Id FROM STUDENT t0, COLLEGE t1 WHERE (t0.college_Id = t1.ID)

I also tested the above script in my DB and its results are as i would expect JPA to return.

ID    name              id       name     col_id 
1   "Bournemouth    2   James   1
1   "Bournemouth    3   Rich    1
1   "Bournemouth    1   Jon 1
1   "Bournemouth    4   tom 1

so i guess this means there must be a problem in my JPA setup? as its obviously not repacking the results correctly.

Thanks Again

----------- Update --------------------------- Further from Pascals suggestions i printed the data to the server log to cut out the Tester interface.

    public List<College> getCollageWithStudents(){
    List<College> s = null;
    try{
        Query query = em.createNamedQuery(College.collegeStudentBasicJoinQuery);
        s = query.getResultList();

        for (int i = 0; i < s.size(); i++) {
                College c = (College) s.get(i);
                System.out.println("College "+c.getId() + "  "+c.getName());
                System.out.println("Amt Students: "+c.getStudents().size());
                for (int j = 0; j < c.getStudents().size(); j++) {
                    Student stu = (Student) c.getStudents().get(j);
                    System.out.println(stu.getId() + "  "+stu.getName());
                }
            }
    }catch (Exception e) { 
        System.out.println(e.toString());
    }
    return s;
 }

The result are as the should be but this is still not reflected in the Glassfish interface.

INFO: College 1  "Bournemouth
INFO: Amt Students: 4
INFO: 2  James
INFO: 3  Rich
INFO: 1  Jon
INFO: 4  tom

Answer 1

Your current query is doing an INNER JOIN and thus returns rows when there is at least one match in both tables. In other words, you'll get the College of each Student that has a College (and this explains why you are getting 4 times the the Bournemouth here).

What about:

SELECT DISTINCT c 
FROM College c JOIN FETCH c.students

That would return distinct College having Student (and fetch the association).