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 ? :-/