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EntityManagerFactory vs EntityManager

Joe Harry
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Joined: Sep 26, 2006
Posts: 9622
    
    2

Guys,

What is the difference between injecting a PersistenceUnit to an EntityManagerFactory instance and injecting a PersistenceContext to an EntityManager instance?


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Ralph Jaus
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Joined: Apr 27, 2008
Posts: 342
Hi,

if you inject the entity manager, it is created, propagated and closed automatically by the container. If you inject the entity manager factory you have to perform all these steps programmatically. Therefore you'll usually inject the entity manager.

Reasons for using an entity manager factory are:

1. In a multi-threaded environment you'll prefer to use thread-safe instance variables. An entity manager factory is thread-safe, while an entity manager is not.

2. You want to use an application-managed persistence context.


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Joe Harry
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Joined: Sep 26, 2006
Posts: 9622
    
    2

Which one to use for a Java SE application?
Ralph Jaus
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Joined: Apr 27, 2008
Posts: 342
Without a container environment you'll have to use an EntityManagerFactory and application-managed persistence context.

The EntityManagerFactory can't be injected, but has to be created by the "Persistence" class like

EntityManagerFactory emf = Persistence.createEntityManagerFactory("persistenceUnitName");
Joe Harry
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Joined: Sep 26, 2006
Posts: 9622
    
    2

Originally posted by Ralph Jaus:
Without a container environment you'll have to use an EntityManagerFactory and application-managed persistence context.

The EntityManagerFactory can't be injected, but has to be created by the "Persistence" class like

EntityManagerFactory emf = Persistence.createEntityManagerFactory("persistenceUnitName");


That"s fine, but after this do I have to say

emf.createEntityManager() in a Java SE application?
Ralph Jaus
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Joined: Apr 27, 2008
Posts: 342
Yes. Furthermore you have to close the EntityManagerFactory and the EntityManager when your program finishes.
[ November 11, 2008: Message edited by: Ralph Jaus ]
Joe Harry
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Joined: Sep 26, 2006
Posts: 9622
    
    2

Good. Thanks for the help!
 
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