I've posted my question into the worng forum so i repost the link here:

http://forum.hibernate.org/viewtopic.php?t=930299

ok so lets talk here
give relationnal model please

CREATE TABLE ph_diadoracommunity_users (
u_id int(10) unsigned NOT NULL default '0',
name varchar(10) ,
email varchar(10) ,
PRIMARY KEY (u_id),
KEY u_id (u_id)
) TYPE=MyISAM;


CREATE TABLE ph_diadoracommunity_users_lv1 (
u_id int(10) unsigned default '0',
address varchar(30) default '0',
KEY u_id (u_id)
) TYPE=MyISAM;



CREATE TABLE ph_diadoracommunity_users_lv2 (
u_id int(10) unsigned NOT NULL default '0',
code varchar(10) default '0',
PRIMARY KEY (u_id),
KEY u_id (u_id)
) TYPE=MyISAM;

The mapping:
<hibernate-mapping>
<class name="ph.news.model.UtenteBase" table="ph_diadoracommunity_users" >
<id name="id" type="int" column="u_id" unsaved-value="0">
<generator class="identity"/>
</id>


<property name="name"/>

<property name="email"/>

<joined-subclass name="ph.news.model.UtenteLivello1" table="ph_diadoracommunity_users_lv1">
<key column="u_id"/>
<property name="address"/>

<joined-subclass name="ph.news.model.UtenteLivello2" table="ph_diadoracommunity_users_lv2">
<key column="u_id"/>
<property name="code"/>
</joined-subclass>
</joined-subclass>

</class>

</hibernate-mapping>

I don't know if this is the right way to model this situation (I think NO) but note that a ph.news.model.UtenteLivello1 (UserLevel1) MUST BE ALSO a ph.news.model.UtenteBase (BaseUser)

what tests have you done with this solution? it seems ok for me

I' ve a Level1User Object with its email, name and its Id: 1.

Now The user id=1 fill a Level 2 registration form, he fills the code than post data, my app should get the UserLevel1 with id=1 and "transform" it in a user of level1 BUT with the same Id. I' can't do it ...

UtenteLivello1 ub=(UtenteLivello1) sess.load(UtenteLivello1.class,new Integer(1));

UtenteLivello2 u2=new UtenteLivello2(ub); //Copy the state

sess.save(u2,new Integer(1));
sess.flush();

stacktrace?

Delete the old object first, I'd say. Besides, Inheritance is not particulary good to model such "type changing" behaviour, consider using aggregation.

ok, I uderstand: I can't delete because I've reltionships with other entities with cascade="delete" attribute.... I'll try to change my design with aggregation!

THX