Managing Entities

Reference

Java Enterprise tutorial

http://piotrnowicki.com/2012/11/types-of-entitymanagers-application-managed-entitymanager/

EntityManager & Persistence Context

see "EntityManager, Transaction and Everything"

Find Entities

em.find(Customer.class, custID);

Managing Entity Life-cycle

Entity states:

• new - has no persistent id and not associated with persistence context

• managed - has id, associated

• detached - has id, not currently associated

• removed - has id, are associated, are scheduled for removal from data store

Persisting:

by invoking EntityManager's persist method

• if cascade=PERSIST or cascade=ALL, related entities will be persisted

• if entity is NEW, will be persisted to database

• if entity is MANAGED, ignored (still cascade to related entities)

• if entity is REMOVED, entity become managed

• if entity is DETACHED, exception will be thrown (IllegalArgumentException)

Removing:

by invoking EntityManager's remove method

• if cascade=REMOVE or cascade=ALL, related entities will be removed

• if entity is NEW - ignored (still cascade)

• if entity is DETACHED - exception

• if entity is REMOVED - ignored

• if entity is MANAGED - will remove from data store when transaction complete or by flush() operatioin

Synchronizing Entity Data to Database

When transaction that the entity is associated with commits, entity persistence state is synchronized.

To force synchronization, call flush() method.

Cascade will work.