Persistence Context and Entity Manager

Persistence Context is nothing but a bag that holds entities. Entity Manager contains persistence context and manages [creates, updates, deletes] the entities that are part of that persistence context. This is shown in the following figure


The life cycle of persistence context depends on whether it is transaction-scoped or extended persistence context.

Transaction-Scoped Persistence Context -

Transaction begins when the bean method is invoked and it ends when the method returns or completes. Similarly transaction-scoped persistence context follows the transaction and is created when the transaction begins and ends after the transaction commits or rolls back.



Extended Persistence Context -

This type of Persistence Context is independent of transaction i.e., the creation or destruction of persistence context is not dependent on transaction begin or transaction end as in the case of transaction-scoped persistence context. Persistence Context will be created when the statefull session bean is created and it is destroyed when the stateful session bean is destroyed.



Note:

There can be many instances of Entity Manager referring to the same single instance of persistence context if all these entity managers are part of the same transaction i.e., entity manager instances part of different ejb's invoked by an ejb which starts and ends the transaction. Please refer the picture below -