Detach an entity from JPA/EJB3 persistence context

What would be the easiest way to detach a specific JPA Entity Bean that was acquired through an EntityManager. Alternatively, could I have a query return detached objects in the first place so they would essentially act as 'read only'?

The reason why I want to do this is becuase I want to modify the data within the bean - with in my application only, but not ever have it persisted to the database. In my program, I eventually have to call flush() on the EntityManager, which would persist all changes from attached entities to the underyling database, but I want to exclude specific objects.

(may be too late to answer, but can be useful for others)

I'm developing my first system with JPA right now. Unfortunately I'm faced with this problem when this system is almost complete.

Simply put. Use Hibernate, or wait for JPA 2.0.

In Hibernate, you can use 'session.evict(object)' to remove one object from session. In JPA 2.0, in draft right now, there is the 'EntityManager.detach(object)' method to detach one object from persistence context.

No matter which JPA implementation you use, Just use entityManager.detach(object) it's now in JPA 2.0 and part of JEE6.

If you need to detach an object from the EntityManager and you are using Hibernate as your underlying ORM layer you can get access to the Hibernate Session object and use the Session.evict(Object) method that Mauricio Kanada mentioned above.

public void detach(Object entity) {
    org.hibernate.Session session = (Session) entityManager.getDelegate();
    session.evict(entity);
}

Of course this would break if you switched to another ORM provider but I think this is preferably to trying to make a deep copy.