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I wrote a stateless EJB method allowing to get an entity in "read-only" mode.
The way to do this is to get the entity with the EntityManager then detach it (using the JPA 2.0 EntityManager).
My code is the following:
@PersistenceContext
private EntityManager entityManager;
public T getEntity(int entityId, Class<T> specificClass, boolean readOnly) throws Exception{
try{
T entity = (T)entityManager.find(specificClass, entityId);
if (readOnly){
entityManager.detach(entity);
}
return entity;
}catch (Exception e){
logger.error("", e);
throw e;
}
}
Getting the entity works fine, but the call to the detach method returns the following error:
GRAVE: javax.ejb.EJBException
at ...
Caused by: java.lang.AbstractMethodError: org.hibernate.ejb.EntityManagerImpl.detach(Ljava/lang/Object;)V
at com.sun.enterprise.container.common.impl.EntityManagerWrapper.detach(EntityManagerWrapper.java:973)
at com.mycomp.dal.MyEJB.getEntity(MyEJB.java:37)
I can't get more information and don't understand what the problem is...
Could somebody help ?
779
You can prevent that by calling the flush method on the EntityManager. After you've done that, you can remove a specific entity from the persistence context by calling the detach method or you can call the clear method to clear the persistence context completely.
detach. Remove the given entity from the persistence context, causing a managed entity to become detached. Unflushed changes made to the entity if any (including removal of the entity), will not be synchronized to the database. Entities which previously referenced the detached entity will continue to reference it.
Entity managers are derived from factory interface called EntityManagerFactory. The configuration used by the entity manager is actually created by the entity manager factory. This definition is separately called a persistent unit. The persistent unit lays out both implicit and explicit settings, entity classes.
EntityManager. The EntityManager API is used to access a database in a particular unit of work. It is used to create and remove persistent entity instances, to find entities by their primary key identity, and to query over all entities. This interface is similar to the Session in Hibernate. Persistence context.
JPA - Detaching an Entity Instance from the Persistence Context. An entity becomes detached (unmanaged) on following actions: serializing or sending an entity remotely (pass by value). Changes to a detached entity (changing fields, removing, refreshing etc) will not be synchronized to the database state.
by clearing the persistence context with EntityManager.clear () serializing or sending an entity remotely (pass by value). Changes to a detached entity (changing fields, removing, refreshing etc) will not be synchronized to the database state. A detached entity still has the database identity.
The EntityManager will create a temporary persistence context, perform the find operation, end the persistence context, and return the detached result object to you. A second call with the same id will return a second detached object.
Overview Persistence providers like Hibernate make use of persistence context to manage the entity lifecycle in an application. In this tutorial, we'll start with the introduction of the persistence context, then we'll see why it's important.
I assume you are using JPA 2.0 with the incorrect version of Hibernate, which doesn't implement the JPA 2.0 spec. The exception tells that the EntityManagerImpl doesn't have the required method.
I suggest upgrading hibernate to 3.5, which is a JPA 2.0 implementation.
108
You can detach all entities with clear but detaching just one entity is not in the JPA 2.0. http://java.sun.com/javaee/5/docs/api/javax/persistence/EntityManager.html
You probably had hibernate impl in your build path, and another implementation on your application server (EclipseLink? or old hibernate version)...
The entityManager.detach(...) is in Hibernate but not in JPA so you need the hibernate impl on your application server to use this function...
35
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