EJB 3 Developer Guide

Chapter 3. Entities

Entities are classes that need to be persisted, usually in a relational database. In this chapter we cover the following topics:

• EJB 3 entities

• Java persistence API

• Mapping an entity to a database table

• Metadata defaults

• Introduction to the entity manager

• Packaging and deploying entities

• Generating primary keys

• Overriding metadata defaults

Introduction

Entities are classes that need to be persisted; their state is stored outside the application, typically in a relational database. Unlike session beans, entities do not have business logic other than validation. As well as storing such entities, we want to query, update, and delete them.

The EJB 3 specification recognizes that many applications have the above persistence ...