What is Persistence Context

Question

I am new to the Java world and JPA  I was studying JPA and came across many new terms like Entity  persistence  While reading  I could not understand the exact definition for Persistence Context   Can anyone explain it in simple laymen terms  What is it to do with the data used in the  Entity   For example  I find this definition too complicated to understand      A persistence context is a set of entities such that for any persistent identity there is a unique entity instance

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A set of persist-able   entity  instances managed by an entity manager instance at a given time  is called persistence context   JPA  Entity annotation indicates a persist-able entity   Refer JPA Definition here

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In layman terms we can say that Persistence Context is an environment where entities are managed  i e it syncs  Entity  with the database

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Persistence Context is an environment or cache where entity instances which are capable of holding data and thereby having the ability to be persisted in a database  are managed by Entity Manager It syncs the entity with database All objects having  Entity annotation are capable of being persisted   Entity is nothing but a class which helps us create objects in order to communicate with the database And the way the objects communicate is using methods And who supplies those methods is the Entity Manager

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A persistence context handles a set of entities which hold data to be persisted in some persistence store  e g  a database   In particular  the context is aware of the different states an entity can have  e g  managed  detached  in relation to both the context and the underlying persistence store   Although Hibernate-related  a JPA provider   I think these links are useful   http   docs jboss org hibernate core 4 0 devguide en-US html ch03 html  http   docs jboss org hibernate entitymanager 3 5 reference en html architecture html  In Java EE  a persistence context is normally accessed via an EntityManager   http   docs oracle com javaee 6 api javax persistence EntityManager html  The various states an entity can have and the transitions between these are described below   http   docs jboss org hibernate entitymanager 3 6 reference en html objectstate html  http   gerrydevstory com wp-content uploads 2012 05 jpa-state-transtition png

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Entities are managed by javax persistence EntityManager instance using persistence context  Each EntityManager instance is associated with a persistence context  Within the persistence context  the entity instances and their lifecycle are managed  Persistence context defines a scope under which particular entity instances are created  persisted  and removed  A persistence context is like a cache which contains a set of persistent entities   So once the transaction is finished  all persistent objects are detached from the EntityManager s persistence context and are no longer managed

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Both the org hibernate Session API and javax persistence EntityManager API represent a context for dealing with persistent data    This concept is called a persistence context  Persistent data has a state in relation to both a persistence context and the underlying database

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A persistent context represents the entities which hold data and are qualified to be persisted in some persistent storage like a database  Once we commit a transaction under a session which has these entities attached with  Hibernate flushes the persistent context and changes insert save  update or delete  on them are persisted in the persistent storage

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Taken from this page   Here s a quick cheat sheet of the JPA world    A Cache is a copy of data  copy meaning pulled from but living outside the database  Flushing a Cache is the act of putting modified data back into the database  A PersistenceContext is essentially a Cache  It also tends to have it s own non-shared database connection  An EntityManager represents a PersistenceContext  and therefore a Cache  An EntityManagerFactory creates an EntityManager  and therefore a PersistenceContext Cache

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While  pritam kumar gives a good overview the 5th point is not true      Persistence Context can be either Transaction Scoped-- the Persistence   Context  lives  for the length of the transaction  or Extended-- the   Persistence Context spans multiple transactions    https   blogs oracle com carolmcdonald entry jpa caching  JPA s EntityManager and Hibernate s Session offer an extended Persistence Context

[java] What is Persistence Context?

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