Fetching data from ternary associations

binnyg · **Joined:** Sat Oct 07, 2006 4:44 pm **Posts:** 4

Hibernate version:3.2.5.ga
Mysql 5.0:

Code:

Class Theme {
    @CollectionOfElements(targetElement = TernaryAssociation.class, fetch = FetchType.LAZY)
   @JoinTable(name = "themes_locations_types", joinColumns = @JoinColumn(name = "theme_id"))
   public Set<TernaryAssociation> getAssociations() {
   } 
}

Class Location {}
Class Type {}

@Embeddable
Class TernaryAssociation {
 @Parent 
 public Theme getTheme(){
 }
 
 @ManyToOne
 @JoinColumn(name = "location_id", nullable = false, updatable = false)
 public Location getLocation() {
 }

 @ManyToOne
 @JoinColumn(name = "type_id", nullable = false, updatable = false)
 public Type getType() {
 }

}

Class A owns the relation.
First, is this the right way to have a ternary association?
Second, I am able to say A.getAssociations to get the list of associations but what I am looking for is give me C where a.id = 1 and b.id=1.

Theme
------------------------
| 1 | description 1
| 2 | description 2
| 3 | description 3

Location
------------------------
| 1 | description 1
| 2 | description 2
| 3 | description 3

Type
------------------------
| 1 | description 1
| 2 | description 2
| 3 | description 3

Theme_Location_Type
------------------------
| 1 | 1 | 1 |
| 2 | 1 | 1 |
| 3 | 1 | 1 |
| 1 | 2 | 1 |
| 2 | 2 | 1 |
| 3 | 2 | 1 |

How do I get, say 2 2 1 from Theme_Location_Type? I have a handle of Theme object. One way of doing it is get the list through theme object and loop until I find the right record.

Thanks

binnyg · **Joined:** Sat Oct 07, 2006 4:44 pm **Posts:** 4

Is this very difficult to achieve or am I doing something wrong?

Cameron McKenzie · **Posted:** Fri Jul 04, 2008 10:35 am

Quote:

One way of doing it is get the list through theme object and loop until I find the right record.

This is certainly a valid way! If there aren't too many objects, it could actually be fairly efficient.

You could also use custom HQL, or even my favorite, use a Criteria Query. The Hibernate3 Criteria API greatly simplifies your queries and makes data access much easier:

Code:

public static void main(String args[]) {
  Session session = HibernateUtil.beginTransaction();
  Criterion c1 = Restrictions.gt("id", (long)2);
  Criterion c2 = Restrictions.lt("id", (long)8);
  Criterion c3 = Restrictions.isNotNull("emailAddress");
  User user = new User();
  user.setEmailAddress(".com");
  Example c4 = Example.create(user);
  c4.enableLike(MatchMode.END);
  c4.ignoreCase();
  Criteria criteria = session.createCriteria(User.class);
  criteria.add(c1);
  criteria.add(c2);
  criteria.add(c3);
  criteria.add(c4);
  List results = criteria.list();
  HibernateUtil.commitTransaction();
  for (int i = 0; i<results.size(); i++) {
    System.out.println(results.get(i).toString());
  }
}