What is a sustainability context?

Question

I am new to Java and JPA. I studied JPA and came across many new terms such as Entity, perseverance. While reading, I could not understand the exact definition for the Save Context .

Can anyone explain this in plain language? What does this have to do with the data used by @Entity ?

For example, I find this definition too difficult to understand:

A persistence context is a collection of entities for which a unique instance of an object exists for any permanent identification.

Answer 1

The persistence context processes a set of entities that store data that should be stored in some persistence store (for example, a database). In particular, the context knows the different states that an object (for example, managed, disconnected) can have in relation to both the context and the main persistence store.

Although Hibernate-related (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 usually accessible through the EntityManager.

http://docs.oracle.com/javaee/6/api/javax/persistence/EntityManager.html

The various states that an entity can have and the transitions between them 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

Answer 2

• Objects are managed using the javax.persistence.EntityManager instance using the persistence context.
• Each instance of EntityManager is associated with a persistence context .
• In the context of persistence, instances of entities and their life cycle are managed .
• A save context defines the area in which instances of specific entities are created, saved, and deleted.
• A persistence context is like a cache that contains a set of persistent entities , so after a transaction is completed , all persistent objects are removed from the EntityManager persistence context and are no longer managed.

Answer 3

Taken from this page :

Here is a quick swap sheet of the JPA world:

• A cache is a copy of data whose copy is pulled from the database but lives outside the database.
• Clearing the cache is the act of returning the changed data to the database.
• PersistenceContext is essentially a cache. It also tends to have its own connection without exchanging data.
• EntityManager is a PersistenceContext (and therefore cache)
• EntityManagerFactory creates an EntityManager (and therefore PersistenceContext / Cache)

Answer 4

Both the org.hibernate.Session and javax.persistence.EntityManager APIs are a persistent data context. This concept is called persistence context. Persistent data has a state in relation to both the persistence context and the underlying database.

Answer 5

A persistent context represents objects that contain data and can be stored in some persistent storage, such as a database. As soon as we commit transaction in the session to which these objects are attached, Hibernate clears the persistent context and the changes ( insert / save, update or delete ) in them are stored in the persistent storage.

Answer 6

"The set of instances that are persisted (entities) managed by the entity manager instance at a given time" is called the persistence context.

JPA @ Optional annotation means an object that retains the ability.

Refer to JPA Definition here.

Answer 7

While @pritam kumar gives a good overview, the fifth point is not true.

Contrast The context can be either the scope of transactions - restraint The context "lives" for the length of the transaction or Extended - Contrast The context spans several transactions.

https://blogs.oracle.com/carolmcdonald/entry/jpa_caching

JPA EntityManager and Hibernate Session offer an extended save context.

Answer 8

From the layman's point of view, we can say that a constant context is an environment in which entities are managed, i.e. it synchronizes the "entity" with the database.