Hibernate does not delete Objects

StefanKNeedsHelp · **Joined:** Thu Nov 26, 2009 8:20 am **Posts:** 23

Hello,
I am working on an Graphical Editor based on GEF. The Model is saved in a database using hibernate.
All of my model-objects are fetched eager.
I have 2 EntityManagers, one to read model data and the second to write changes back to database via merge
First reading example:

Code:

static public Diagram findByProjectAndName(String pProjectName, String pName) {
      Diagram lResult = null;
      sReadingManager.clear(); 
      sReadingManager.getTransaction().begin();
      List<Diagram> lDiagrams = sReadingManager.createQuery(
            "from Diagram d where d.project.name = '" + pProjectName + "' " +
            "and d.name = '" + pName + "'")
            .getResultList();
      if (lDiagrams.size() == 1) {
         lResult = lDiagrams.get(0);
      }
      sReadingManager.getTransaction().commit();
      return lResult;
   }

Second, write data back to db:

Code:

   static public void mergeDiagram(Diagram pDiagram) {
      sWritingManager.getTransaction().begin();
      Diagram lDia = sWritingManager.merge(pDiagram);
      sWritingManager.getTransaction().commit();
      
   }

Everything works fine so far. I get the diagram, do some changes to its model and then clall merge after saving.
But there is still one Problem left, if I delete an element of the diagram, hibernate will not delete it in the database. Hibernate will only set the references on the deleted element to null:
DEBUG SQL:393 - update DiagramElement set name=?, viewInfo=?, diagram_fk=? where DIAGRAMELEMENT_ID=?
DEBUG SQL:393 - update DiagramElement set diagram=null where diagram=?

Do I have to delete the element explicit in a query or am I doing something wrong?

I would appreciate any help!

Thanks in advance & best regards.

Cameron McKenzie · **Posted:** Wed Feb 03, 2010 6:13 pm

Are you just making the object null, or calling delete? Making it null won't delete it. Nullifying it will likely just delete an association with an aggregating object.

StefanKNeedsHelp · **Joined:** Thu Nov 26, 2009 8:20 am **Posts:** 23

Hello and first of all thanks for your reply!
How should I delete it?
At the moment I am removing the Element from the List of DiagramElements in my Diagram via list.remove(diagramElement)
So what else should I do to delete the object in database, too.
Please be aware that I am working with detached objects and all my changes on the model are updated at the end.

Thanks for your help.
Best regards
Alex

StefanKNeedsHelp · **Joined:** Thu Nov 26, 2009 8:20 am **Posts:** 23

Hello again,
I figured out that JPA causes the problem with deleting detached objects.
During the long unit of work, the user can change the model outside of a transaction (detached objects!), so if the user deleted an object it is not possible to call lEntitityManager.remove(modelObject)
So I need something which automatically removes all orphans from the database. In hibernate an annotiation CascadeType.DELETE_ORPHANS exists, but in JPA there is no annotation like this supported.
Perhaps there is an easy way to get the same functionality with JPA and if so I would appreciate any example :)
But there is still another problem left:
Calling sWritingManager.merge(pDiagram) causes to reload all instances.
For example before merging, DiagramElement A has the object_id 1 and after merging it has the object_id 2.
But not all instances in the application are reloaded. If I had any references to DiagramElement A, the reference is now out of date (because the reference is on DiagramElement A with object_id 1).
Any opportunities to solve this?
Thanks in advance & best regard,
Alex