Hibernate child object creation problem

Question

hi,
i have two java classes named "user" and "writer"
writer is subclass of user.
with hibernate mapping files , i 'm mapping objects with table-per-subclass strategy...
here is my mapping code:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
<class name="User" table="User">
<id name="id" type="long" column="id">
<generator class="increment"/>
</id>
<property name="userName" column="userName"/>
<joined-subclass name="Writer" table="Writer">
<key column="user_id"/>
<set name="articles" table="writer_articles" lazy="false">
<key column="user_id"/>
<many-to-many column="Article_id"
unique="true"
class="Article"/>
</set>
</joined-subclass>
</class>
</hibernate-mapping>
when i create a writer(child) object, writer record is inserted to two tables with the same id column.it's good.not a problem
but when i create a user(parent) object then if i want to change role of user to writer it's a problem...
for example:
User user=new User(..); user is inserted to user table with id =10
i want to save same user as a writer with same id number to writer table
Writer writer =new Writer(..); writer must be inserted to writer table with id=10_
in hibernate writer is inserted to writer table with different id number...
what must i do to solve problem ??

Answer 1

nobody replied about my problem...
i searched on google and learned some information
i think ,there is two way to resolve this issue:
1) -delete parent record - and -create child record-
but this could not be efficient.
2) insert child record with same id number to child table manually (by HQL )
Regards.