ClassCast for similar objects

florian79 · **Joined:** Thu Sep 21, 2006 2:49 am **Posts:** 24

ClassCast for similar objects

Hibernate version: 3.2.0 CR4 with Annotationen

DB: MySQL

I hava the following class hirarchie (using Table per subclass strategie):
MethaBean extends Object
Person extends Metha Bean
Employee extends Person
User extends Person

Depending on the context the same person can be a User or an Employee. how to do the cast?

The following code prints always an employee, because I created it as an employee. but how can I convert (cast) it to an User or a Person.
(The second object gets a ClasCastException, of course)

Code:

Session session = SessionFactory.currentSession(); 
        Long lID = new Long(1030); 
        Object bean1 = null; 
        Object bean2 = null; 
        Object bean3 = null; 
        try 
        { 
            bean1 = (Person)session.get(Person.class, lID); 
            bean3 = (Employee) session.get(Employee.class, lID); 
            bean2 = (User) session.get(User.class, lID); 
            
        } 
        catch (ClassCastException e) 
        { 
            e.printStackTrace(); 
        } 
        System.out.println("1 Person :" + bean1); 
        System.out.println("2 User :" + bean2); 
        System.out.println("3 Employee :" + bean3); 
 

Results:

Code:

log4j:WARN No appenders could be found for logger (org.hibernate.cfg.annotations.Version). 
log4j:WARN Please initialize the log4j system properly. 
[2006.09.21][com.co.util.hibernate.SessionFactory][][DEBUG]: hibernate SessionFactory created by 
[2006.09.21][com.co.util.hibernate.SessionFactory][][DEBUG]: hibernate session opened by 
java.lang.ClassCastException: com.co.util.beans.Employee 
at com.co.test.HibernateTest.main(HibernateTest.java:39) 
1 Person :co.util.beans.Employee: Wasle Florian (1030) 
2 User :null 
3 Employee :co.util.beans.Employee: Wasle Florian (1030) 

Thanks,
Florian

pasha · **Joined:** Sat Nov 27, 2004 4:13 am **Posts:** 137

Wll forget about hibernate!! how could you do that in plain Java?
can you change class of an object?!

Hibenate fetches an object from database, what class should it be? User or Employee? when your object can be both!

Maybe you must refactor your code, for example "Employee extends User" or something like this

florian79 · **Joined:** Thu Sep 21, 2006 2:49 am **Posts:** 24

Yes I want to fetch the data from datbase and crete an object using this data. It should be possible to get the object as Person, User OR Employee. The session context just binds one object either a Person or an User, of course. And the next time with a new session I want to fetch it as another object.

It is not possible in plain java because if I cast from Employee to User the Employee-specific data would get lost. But that could not happen with o/r-mapping - there we have diferent database tables for each object.

I think that would be a nice feacher!