Configuring a Primary Key for an EJB 2.1 Entity Bean With Bean-Managed Persistence

Every EJB 2.1 entity bean with bean-managed persistence must have a primary key field.

You can configure the primary key as a well-known Java type (see "Configuring a Primary Key Field for an EJB 2.1 Entity Bean With Bean-Managed Persistence") or as a special type that you create (see "Configuring a Primary Key Class for an EJB 2.1 Entity Bean With Bean-Managed Persistence").

For more information, see "What is a Primary Key of an Entity Bean With Bean-Managed Persistence?"

For EJB 2.1 entity beans with bean-managed persistence, you are responsible for assigning primary key values, typically in the ejbCreate method (see "Configuring a Life Cycle Callback Method for an EJB 2.1 Entity Bean With Bean-Managed Persistence").

Configuring a Primary Key Field for an EJB 2.1 Entity Bean With Bean-Managed Persistence

For a simple EJB 2.1 entity bean with bean-managed persistence, you can define your primary key to be a well-known Java type as follows:

• Code your bean's ejbCreate method to return the primary key class type (see "Implementing an EJB 2.1 Entity Bean With Bean-Managed Persistence")

• Configure your deployment XML to use it (see "Using Deployment XML")

Using Deployment XML

Example 15-1 shows the ejb-jar.xml file <entity> element <prim-key-class> and <primkey-field> subelements configured to specify a primary key as well-known Java type Integer.

Example 15-1 ejb-jar.xml for Primary Key Field With Type Integer of EJB 2.1 Entity Bean With Bean-Managed Persistence

<enterprise-beans>
  <entity> 
    <display-name>Employee</display-name>
    <ejb-name>EmployeeBean</ejb-name>
    <local-home>employee.EmployeeLocalHome</local-home>
    <local>employee.EmployeeLocal</local>
    <ejb-class>employee.EmployeeBean</ejb-class>
    <persistence-type>Bean</persistence-type>
    <prim-key-class>java.lang.Integer</prim-key-class>
    <reentrant>False</reentrant>
    <cmp-version>2.x</cmp-version>
    <abstract-schema-name>Employee</abstract-schema-name>
    <cmp-field><field-name>empNo</field-name></cmp-field>
    <cmp-field><field-name>empName</field-name></cmp-field>
    <cmp-field><field-name>salary</field-name></cmp-field>
    <primkey-field>empNo</primkey-field>
    </entity>
...
</enterprise-beans>

Configuring a Primary Key Class for an EJB 2.1 Entity Bean With Bean-Managed Persistence

If your primary key is more complex than a well-known Java data type, then you can define your own primary key class.

Your primary key class must have the following characteristics:

• be named <name>PK

• be public and serializable

• provide a constructor for creating a primary key instance

Your class may contain any number of instance variables used to form the primary key. Instance variables must have the following characteristics:

• primitive object types

• serializable types

• types that can be mapped to SQL types

• types that are a legal Value Type in RMI-IIOP

• types that provide a suitable implementation of the hashCode() and equals(Object) methods

Once the primary key class is defined (see "Using Java"), to use it in an EJB, you must do the following:

• Code your bean's ejbCreate method to return the primary key class type (see "Implementing an EJB 2.1 Entity Bean With Bean-Managed Persistence")

• Configure your deployment XML to use it (see "Using Deployment XML")

Using Java

Example 15-2 shows an example primary key class.

Example 15-2 Primary Key Class Implementation for a EJB 2.1 Entity Bean With Bean-Managed Persistence

package employee;

import java.io.*;
import java.io.Serializable;
...

public class EmployeePK implements java.io.Serializable {
  public Integer empNo;

  public EmployeePK() {
    this.empNo = null;
  }

  public EmployeePK(Integer empNo) {
    this.empNo = empNo;
  }
}

Using Deployment XML

As Example 15-3 shows, you define the primary key class within the ejb-jar.xml file <prim-key-class> element. You define each primary key class instance variable in a <cmp-field><field-name> element using the same variable name as that used in the primary key class.

Example 15-3 ejb-jar.xml for Primary Key Class and Its Instance Variables of EJB 2.1 Entity Bean With Bean-Managed Persistence

<enterprise-beans>
  <entity>
    <description>no description</description>
    <display-name>EmployeeBean</display-name>
         <ejb-name>EmployeeBean</ejb-name>
         <local-home>employee.LocalEmployeeHome</home>
         <local>employee.LocalEmployee</remote>
         <ejb-class>employee.EmployeeBean</ejb-class>
         <persistence-type>Bean</persistence-type>
        <prim-key-class>employee.EmployeePK</prim-key-class>
         <reentrant>False</reentrant>
         <cmp-version>2.x</cmp-version>
         <abstract-schema-name>Employee</abstract-schema-name>
        <cmp-field><field-name>empNo</field-name></cmp-field>
         <cmp-field><field-name>empName</field-name></cmp-field>
         <cmp-field><field-name>salary</field-name></cmp-field>
      </entity>
</enterprise-beans>