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Section 1. Introduction

Introduction to CMP/CMR

This tutorial is designed to introduce you to Container Managed Persistence (CMP)

and Container Managed Relationships (CMR) in Enterprise JavaBeans 2.0 (EJB).

These features are particular to EJB entity beans that are typically long lived as

compared to session beans that are normally transitory.

Enterprise JavaBeans (EJB) 2.0 extends the earlier version 1.1 by adding advanced

support for entity beans as follows:

updated container managed persistence for entity beans

support for container managed relationships

EJB Query Language (EJB QL) for portable

select

and

find

query methods defined

in the deployment descriptor

The addition of local interfaces and local home interfaces to optimize access from

other beans in the same container.

If you want to buy or sell components, you will most likely want a layer of persistence in

your components to work cross platform on application servers (for example, IBM

WebSphere, BEA WebLogic, JBoss/Tomcat, etc.) and persistence storage systems (for

example, Oracle, DB2, etc.). You do not have to write low level Java Database

Connectivity (JDBC) calls in your EJBs to add these features, a great reducer of time

and complexity. Once you get the hang of CMP/CMR, it is faster to write entity beans

using this technology, than using low level JDBC inside of bean managed persistence

(BMP) beans.

Should I care about CMP/CMR?

What does this mean to you? Well, for starters, you do not have to write low level

JDBC calls and, you do not have to write code to manage relationships. It is all built

into the EJB framework. Your interface to relationships is through the pervasive

java.util.Collection

and

java.util.Set

which most EJB developers are

already familiar with. Very cool!

This additional feature includes support for JavaBeans component patterns for

persistent fields, inside of the entity bean. Thus, instead of making your class variables

public    which has always felt strange to me    you create get and set methods

following the JavaBean s standard naming pattern we all know and love.

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Introducing EJB CMP/CMR, Part 1 of 2