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Section 9. Example 2: Finder methods and EJB QL

Finder methods and EJB QL

The Enterprise JavaBeans Query Language (EJB QL), a subset of SQL92, allows the

definition of finder methods in the deployment descriptor for entity beans with

container managed persistence. EJB QL is a powerful little language that is easy to

learn and use. Like SQL, EJB QL is easy to learn, but takes some time to master.

EJB QL was extended to navigate over CMR relationships. The EJB container is

responsible for translating EJB QL queries into the query language of the persistent

datastore, for example, SQL 92 for IBM DB2. This translation results in creating finder

methods that are more portable. This allows enterprise component vendors to sell

components that work on more target platforms. The third tutorial in this series will

cover EJB QL in detail. Here is a small taste.

Creating a

findAll()

method for

UserBean

Finder methods allow entities to be found based on a criteria. Finder methods are

defined in the home interface. Prior to EJB 2.0 it was up to the developer to create his

own finder methods (or a propietary EJB vendor solution). The developer would

declare a finder method in the home interface let s say

findAll()

then the developer

would define the corresponding definition of the finder method in the bean

implementation for example

ejbFindAll()

.

Listing 11: Home interface for

findAll()

/** Home interface now has findAll method **/

package com.rickhightower.auth;

import java.util.Collection;

public interface LocalUserHome extends EJBLocalHome {

public Collection findAll() throws FinderException;

}

With EJB 2.0 CMP, you merely define the finder method definition in the deployment

descriptor using EJB QL. You still have to declare the finder method in the home

interface. Note that the finder method

public Collection findAll() throws

FinderException

is declared in the home.

Introducing EJB CMP/CMR, Part 1 of 2

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