JPA Tutorial

1. jpa-entity-class
- @javax.persistance.Entity
- public, protected no-argument contructor
- class not declare final, no method, persistence instance variables is final.
- if an entity is passed by value as detached object. such as through a session bean remote. class must by implementaion Serialization 
- Entity may extends both entity and non-entity class. 
- fields: not annotated 



2. Class Level architecture
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- Entity Manager Factory: It creates and manages multiple Entity Manager
- Entity Manager: It's interface, it manages the persistence operations on objects. It works like a factory for Query instacnce
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