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I am currently having a problem with understanding a concept of JPA. I am currently using/developing recent EclipseLink, Glassfish, Derby database to demonstrate a project. Before I develop something in much bigger picture, I need to be absolutely sure of how this PersistingUnit work in terms of different scopes. I have bunch of servlets 3.0 and currently saving user's associated entity classes in the request.session object (everything in the same war file). I am currently using Application-managed EntityManager using EntityManagerFactory and UserTransaction injection. It works smooth when it is tested by myself. The different versions of entities occur when 2 people accessing the same entities at the same time. I want to work with managed beans cross the same WAR, same persistence unit if possible. I have read http://docs.oracle.com/javaee/6/tutorial/doc/bnbqw.html and bunch of explanations of those scopes which don't make sense at all for me. Long story short , what are the usage and difference of app and container managed EntityManagers?

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