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About EntityManager

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Manual
33

Working with JPA Entity Objects

this state the object is not yet associated with an EntityManager and has no representation in ... via an EntityManager’s persist method, which must be invoked within an active transaction. On transaction commit, the owning EntityManager stores the new entity object to the database. More details on storing objects
Manual
30

Chapter 3 - Using JPA

Explains how to store, retrieve, update and delete entity objects using JPA.
Manual
30

CRUD Operations with JPA

Explains how to use JPA for CRUD database operations (persist, retrieve, update, remove).
Manual
30

Deleting JPA Entity Objects

Explains how to use JPA to delete (remove) entity objects from the database.
JPA Doc
30

JPA Reference (JavaDoc)

Java/JPA API Reference (based on the JPA 3 JavaDoc)
Manual
26

Setting and Tuning of JPA Queries

on which they were invoked). Flush Mode (setFlushMode) Changes made to a database using an EntityManager ... of other EntityManager instances). JPA implementations can easily make uncommitted changes visible in ... the application, either at the EntityManager level as a default for all the queries in that EntityManager
Manual
25

Shared (L2) Entity Cache

Every EntityManager owns a persistence context, which is a collection of all the entity objects ... an entity object that is already managed by the EntityManager returns the existing instance from ... is one EntityManager. This section describes a level 2  (L2) cache of entity objects, which is managed
Manual
25

CRUD Database Operations with JPA

Given an EntityManager, em, that represents a JPA connection to the object database, we can use ... an ordinary Java object. It then becomes associated with an EntityManager and with its transaction (as ... can become productive very quickly. The EntityManager object serves as the factory for Query instances
Manual
20

DELETE Queries in JPA/JPQL

the entity objects into an EntityManager. Removing these objects from the EntityManager within an active ... them, but it should be used cautiously because bypassing the EntityManager may break its synchronization with the database. For example, the EntityManager may not be aware that a cached entity object in its persistence
Manual
18

Locking in JPA

another EntityManager) since it was retrieved by the current updater. Optimistic locking ... another EntityManager instance) currently holds a PESSIMISTIC_WRITE lock on that database object. A PESSIMISTIC ... .lock(e1, lockMode1); em2.lock(e2, lockMode2); em1 and em2 are two EntityManager instances