Trigger JPA callbacks only once per transaction or batch - jpa

Question

I am deleting rows in a batch as follows (in an EJB).
int i=0;
List<Category> list = // Sent by a client which is JSF in this case.
for(Category category:list) {
if(++i%49==0) {
i=0;
entityManager.flush();
}
entityManager.remove(entityManager.contains(category) ? category : entityManager.merge(category));
}
Where Category is a JPA entity.
There is a callback that listens to this delete event.
#ApplicationScoped
public class CategoryListener {
#PostPersist
#PostUpdate
#PostRemove
public void onChange(Category category) {
//...
}
}
This callback method is invoked as many times as the number of rows which are deleted. For example, this method will be called 10 times, if 10 rows are deleted.
Is there a way to invoke the callback method only once at the end of a transaction i.e. as soon as the EJB method in which this code is executed returns or at least per batch i.e. when entityManager.flush(); occurs? The former is preferred in this case.
Additional Information :
I am doing some real time updates using WebSockets where clients are to be notified when such CRUD operations are performed on a few database tables. It is hereby meaningless to send a message to all the associated clients on deletion of every row which is performed in a batch - every time a single row is deleted. They should rather be notified only once/at once (as soon as) a transaction (or at least a batch) ends.
The following JPA 2.1 criteria batch delete approach does not work because it does not directly operate upon entities. No JPA callbacks will be triggered by this approach neither by using its equivalent JPQL.
CriteriaBuilder criteriaBuilder=entityManager.getCriteriaBuilder();
CriteriaDelete<Category> criteriaDelete = criteriaBuilder.createCriteriaDelete(Category.class);
Root<Category> root = criteriaDelete.from(entityManager.getMetamodel().entity(Category.class));
criteriaDelete.where(root.in(list));
entityManager.createQuery(criteriaDelete).executeUpdate();
I am using EclipseLink 2.5.2 having JPA 2.1

Answer 1

Unfortunately JPA provides entity callbacks, which are required to be called for each entity instances they listen on, so you will need to add in your own functionality to see that the listener is triggered only once per batch/transaction etc. The other alternative is to use provider specific behavior, in this case EclipseLink's session event listeners: https://wiki.eclipse.org/Introduction_to_EclipseLink_Sessions_(ELUG)#Session_Event_Manager_Events to listen for the PostCalculateUnitOfWorkChangeSet event or some other event that gets triggered when you need.