[jboss-user] [EJB 3.0] - Re: EJB QL/ JPQL and search for inheritance

[andydale]

Joachim,

I have never attmepted to do an instanceof with the inheritance type of a single table per hierarchy.  Prehaps you should investigate some other strategies, namely table per subclass as i think this will provide you with the functionality you would like, like so:


  |         //create query
  |         Query tmpQuery = mEntityManager.createQuery("FROM Tag t");
  | 
  |         //get query result
  |         ArrayList<Tag> queryResult = (ArrayList<Tag>)tmpQuery.getResultList();
  | 
  |         //get iterator
  |         Iterator it = testList.iterator();
  |         
  |         //loop
  |         while (it.hasNext()) {
  |             Tag element = (Tag) it.next();
  |             
  |             if(element instanceof PlaceMark) {
  |                 //DO STUFF :-)                   
  |             }                     
  |         }
  | 

In your top level parent class you just need to annotate like so:

@Inheritance(strategy = InheritanceType.JOINED)

and i just have a getter and setter for the id in this parent class, and not in the sub-classes(children). All you should need to do in the children classes is just extend the parent class.

To persist, just create and persist a child object and it automatically create and persists the parent objet with the correct attributes.


Cheers,

Andy

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