Writing EJB Expression-Style Finder Methods

How to write expression-style finder methods for CMP entity beans.

About this technique	Details
Category	Enterprise JavaBean Techniques
Description	You'll learn about: Writing an expression-based finder method Specifying the expression using the JAR Designer Specifying the expression using the SilverCmd DeployEJB XML file
Related reading	See the chapter on writing entity beans in the Programmer's Guide

Writing an expression-based finder method   

Expression-based finder methods are finders that can be defined using the SilverStream expression language. You define the finder expression during the EJB JAR deployment process.

Setting up

To set up, follow these steps:

• Write a finder method declaration in the bean's home interface.

• Add the bean class, the home, and remote interfaces to the EJB JAR.

• Add the deployment descriptor information.

• Deploy the EJB JAR.

Specifying the expression using the JAR Designer   

You can use the JAR Designer to do the following:

1. In the Deployment pane, highlight the findByLikeness method and open the Property Inspector.

2. Make sure Type is Expression.

3. Open the Expression builder.

4. Choose the companyid field.

5. Choose the Like operator (from String Operators).

6. Choose the javaLangString0 parameter.

   The expression builder presents the list of parameters included in the finder method's signature. The parameter names include the data type and the parameter's position as part of the variable name. For example, if the Finder method definition included another parameters, which was an integer, the expression builder would include javaLangInt1.

   

7. Close the Property Inspector. The finder method is mapped.

Specifying the expression using the SilverCmd DeployEJB XML file    

To specify an expression-based finder method in the DeployEJB XML input file, you need to add entries for tags in the obj_FinderMethod subsection of the input file. The following example shows how to define the Company demo finder method described in the previous section.

  <obj_finderMethod> 
     <obj_method> 
       <name>findByLikeness</name> 
        <methodParams type="String"> 
          <el>java.lang.String</el> 
        </methodParams> 
     </obj_method> 
     <finderMethodType>Expression</finderMethodType> 
      <whereClause>Companies.companyname like 
                       javaLangString0</whereClause> 
  </obj_finderMethod> 

• The <finderMethodType> tag must be Expression.

• The <whereClause> tag for an expression must use the SilverStream expression language syntax.

• For more information on this syntax see the chapter on expressions in the Programmer's Guide.