Problem deleting value-type object from Collection in Hibernate

[kwame Iwegbue]

I'm using Hibernate. I have no problem deleting Entities (with ID value) but I seem to be having some trouble deleting regular Value type objects from a Collection. It seems to me that if you call remove(), the object should be removed. However, after doing this, the Object is removed from the Set, but when I load the View, the Object is again retrieved from the Set and displayed?!

  
 
/**
 * Stripes event handler that deletes the selected diagnosis from the visits Collection
 * of diagnoses. 
 */
@HandlesEvent("delete")
public Resolution deleteDiagnoses()  {
Visit v = visitDAO.findById(getVisit_id(), true);  //Visit is an Entity
 
Set<Diagnosis> diagnoses = v.getDiagnoses();
Diagnosis dxForDelete = null; //A value type object. (no DB Id)
 

for (Iterator iter = diagnoses.iterator(); iter.hasNext() ;  )  {
Diagnosis element = (Diagnosis) iter.next();

if(element.getName().contains(getDiagnosis().getName())) {
    dxForDelete = element;  //remove is called outside loop to avoid ConcurrentModificationException
    break;
}

}
diagnoses.remove(dxForDelete);
visitDAO.flush();

return getContext().getSourcePageResolution();
}
 
  

[ August 15, 2007: Message edited by: kwame Iwegbue ]

[Shailesh Kini]

Hi Kwame,

If I understand your question correctly....

Removing an entity (Diagnoses) from the Collection does not remove it from the database. It's just removed from the Collection. The flush just get's whatever is in the database and those records still exist. You might want to call a hibernate session's remove on the Diagnoses objects to get the desired effect.

[kwame Iwegbue]

Thanks Shailesh,

The thing is, the Diagnoses object is not an entity, but a Collection of value types without a database identity. They are embedded in another class, which is an Entity. When I remove one of the objects in the List, it is deleted from the List as expected, but when the List is called from the JSP, it is again loaded from the database. How can I overcome this? I can't call session.delete() because I dont want to delete the Entity.
[ August 16, 2007: Message edited by: kwame Iwegbue ]

[kwame Iwegbue]

Can someone please help with this problem. Its been over a week, and I still can't figure it out. Let me rephrase the question:
Is there a special way of handling Collections of objects in Hibernate, when those objects do not have a database identity. I know that Objects with identiy, mapped in a Collection with *-to-many, are managed by the Hibernate session and can be removed by session.remove() etc; but how about regular objects?

When I try to remove them like from the Collection, they are reloaded from the database when the Collection is again accessed. Please help!!!
[ August 22, 2007: Message edited by: kwame Iwegbue ]

[Edvins Reisons]

I see a contradiction here: how can you load from a database a collection of
objects that have no database identity?

[kwame Iwegbue]

Here's whats going on:

  
@Entity
@org.hibernate.annotations.Entity(dynamicInsert = true, dynamicUpdate = true)
@Table(name = "VISIT")
public class Visit implements Serializable {
 

@Id @GeneratedValue
@Column(name="VISIT_ID")
private Long id;
 
...
 
@org.hibernate.annotations.CollectionOfElements
@JoinTable(name = "DIAGNOSES", joinColumns = @JoinColumn(name = "VISIT_ID"))
private Set<Diagnosis> diagnoses = new HashSet<Diagnosis>();
 
...
 
  

So Visit is an Entity (has database identity) and Diagnosis is a Value type (has no database identity).

I can manage a Visit object with

  
            getSession().saveOrUpdate(visit);  
            getSession().delete(visit);
            
 
 

However, this won't work with Diagnosis. So if I want to delete a DIagnosis object, which is in a Set that is mapped to a Visit object, I do this:

  
...
Visit v = visitDAO.findById(getVisit_id(), true);
Set<Diagnosis> diagnoses = v.getDiagnoses();

for (Iterator iter = diagnoses.iterator(); iter.hasNext();    )   {
Diagnosis element = (Diagnosis) iter.next();
v.getDiagnoses().remove(element);
} 
...
 

So this works, and removes the Diagnosis from the Collection, however, when Visit is loaded again, the "deleted" Diagnosis is still present in the Collection!
[ August 23, 2007: Message edited by: kwame Iwegbue ]

[Edvins Reisons]

What is visitDAO?
[ August 24, 2007: Message edited by: Edvins Reisons ]

[kwame Iwegbue]

visitDAO is a data access object that loads the Entity, Visit from the database.

Has no one out there using Hibernate, run into this type of situation that I describe in this question, or is it still unclear what I'm asking, or is it just a dumb question. Can some hibernate guru please help me with this!!

[Edvins Reisons]

I asked the question about visitDAO because the persistence behavior of the
contained collection may depend on what is inside the DAO. Before digging into the DAO, let's make sure that the situation is as you describe: simple (non-collection) properties of the entity do get persisted to the database,
but the collection doesn't. Have you checked this?

[kwame Iwegbue]

Thanks.
All other properties of the containing Entity (Visit) are managed correctly by hibernate, including other Collections, which are Collections of Entities mapped by one-to-many association. Even this particular troublesome Collection of Value type objects (Diagnoses) is managed correctly in every way, except when it comes to delete. According to everything I've read so far, removing a Value type object from a Collection should cause it to be deleted as well.

[Edvins Reisons]

Could it be that the Visit entity that you return from the DAO is detached?

[kwame Iwegbue]

detached huh?, Well I'm using the Open session in View pattern, i.e the whole request-response cycle is wrapped in a Hibernate Session. So I guess it could be detached after the delete method exits or something. But why would that be a problem. Do I need to re-attach it after the loop or what?

[Edvins Reisons]

The problem with a detached entity is that whatever you do to it is not going to be persisted to the database. So, this is definitely worth checking, although I only half believe that this is what is going on here.
Please post the code of the DAO class(es) that get called so that we can see better what is happening.

[kwame Iwegbue]

I agree with you about detached objects, but my feeling was that with Open Session in View Pattern (which is what I'm using) , the persistence-context (unit of work) is wrapped by the request-responce cycle (in a servlet filter) so you application objects never get detached on their own, unless I close the persistence context prematurely. So I'm not sure this is the problem.

The Code for my VisitDAO is

  
public class VisitDAOHibernate extends GenericHibernateDAO<Visit, Long> implements
                                    VisitDAO {
...
 
  

the actual method is from GenericHibernateDAO, which is

   
 
public class GenericHibernateDAO<T, ID extends Serializable> 
             implements GenericDAO<T, ID> {
...
 
@SuppressWarnings("unchecked")
public T findById(ID id, boolean lock) {
T entity;
if(lock)
entity = (T) getSession()
    .load(getPersistentClass(), id, LockMode.UPGRADE);
else
entity = (T) getSession()
    .load(getPersistentClass(), id);

return entity;
}
 

The rest of the methods in the DAO are simply database queries.

[Edvins Reisons]

What happens when you move the entity manipulation code into the DAO?
I think it belongs there anyway, and if the Session is, as it is in a
sample that I have here , a member variable of the DAO, doing so
would remove questions about visibility between the Session and the entity that you are modifying.