Application Identity

Whenever you want to control object identity with your own source code, you have to use application identity. This requires also a primary key class beside your business class. This class must fullfil the following requirements:

• The class has to be public .
• The class has to implement the interface Serializable .
• The class has to offer a public constructor that has no parameters or uses the default constructor.
• All non-static fields have to be serializable.
• All serializable non-static fields have to be public.
• The names of all non-static fields in the class have to include the primary key fields of the persistent class.
• The implementation of the methods equals() and hashCode() has to consider all the values of the primary keys.
• The primary key class must have a constructor which takes a String as argument (created by the toString() method).
• The method toString() must return the unique object id as String.

Sample class Person:

public class Person
{
  . . .
  private Integer id; // primary key field
  private String name; // jdo persistent field
  private Integer xyz; // jdo persistent field
  ...
}

// primary key class for class Person
public class PersonKey implements Serializable
{
  public Integer id; // primary key field

  public PersonKey()
  {
  }

  public PersonKey(String key)
  {
    id = Integer.parseInt(key);
  }

  public boolean equals(Object o)
  {
    if (o != null && o instanceof PersonKey)
     { 
     return id.equals(((PersonKey)o).id); 
     }
    return false;
  }

  public int hashCode()
  {
    return id.hashCode();
  }

  public String toString()
  {
    return Integer.toString(id);
  }
}

<class name="Person" identity-type="application"
  objectid-class="com.test.PersonKey">
  
  <field name="id" default-fetch-group="true" primary-key="true" />
  <field name="name" default-fetch-group="true" />
  ...
</class>