Hi everybody,

For example, I have two classes : Person and Employee (Employee is a subclass of Person). Person : has a lastname and a firstname. Employee : has also a salary.

On the client-side, I have a single HTML form where i can fill the person informations (like lastname and firstname). I also have a "switch" between "Person" and "Employee", and if the switch is on Employee I can fill the salary field.

On the server-side, Servlets receive informations from the client and use the Hibernate framework to create/update data to/from the database. The mapping i'm using is a single table for persons and employee, with a discriminator.

I don't know how to convert a Person in an Employee.

I firstly tried to :

• load the Person p from the database
• create an empty Employee e object
• copy values from p into e
• set the salary value
• save e into the database

But i couldn't, as I also copy the ID, and so Hibernate told me they where two instanciated ORM with the same id.

And I can't cast a Person into an Employee directly, as Person is Employee's superclass.

There seems to be a dirty way : delete the person, and create an employee with the same informations, but I don't really like it..

So I'd appreciate any help on that :)

Some precisions :

The person class :

public class Person {

    protected int id;

    protected String firstName;
    protected String lastName;

    // usual getters and setters
}

The employee class :

public class Employee extends Person {

   // string for now
   protected String salary;

   // usual getters and setters
}

And in the servlet :

// type is the "switch"
if(request.getParameter("type").equals("Employee")) {
  Employee employee = daoPerson.getEmployee(Integer.valueOf(request.getParameter("ID")));
  modifyPerson(employee, request);
  employee.setSalary(request.getParameter("salary"));
  daoPerson.save(employee );
}
else {
  Person person = daoPerson.getPerson(Integer.valueOf(request.getParameter("ID")));
  modifyPerson(employee, request);
  daoPerson.save(person);
}

And finally, the loading (in the dao) :

public Contact getPerson(int ID){
  Session session = HibernateSessionFactory.getSession();
  Person p = (Person) session.load(Person.class, new Integer(ID));
  return p; 
}

public Contact getEmployee(int ID){
  Session session = HibernateSessionFactory.getSession();
  Employee = (Employee) session.load(Employee.class, new Integer(ID));
  return p; 
}

With this, i'm getting a ClassCastException when trying to load a Person using getEmployee.

XML Hibernate mapping :

<class name="domain.Person" table="PERSON" discriminator-value="P">
        <id name="id" type="int">
            <column name="ID" />
            <generator class="native" />
        </id>

        <discriminator column="type" type="character"/>


        <property name="firstName" type="java.lang.String">
            <column name="FIRSTNAME" />
        </property>
        <property name="lastName" type="java.lang.String">
            <column name="LASTNAME" />
        </property>

  <subclass name="domain.Employee" discriminator-value="E">
    <property name="salary" column="SALARY" type="java.lang.String" />
  </subclass>
</class>

Is it clear enough ? :-/