Hibernate version: 2.6

I have problem in saving the sub - class data
I have one Object Person and Other object Teacher which extends Person.

Person
{
id Long
name String
Role String (default values TEACHER,STUDENT)
}


Teacher extends Person
{
subject - String
}



TABLES

PERSON: ID NAME ROLE
TEACHER : ID (Foreign Key to PERSON), SUBJECT

Based on Role I have to Save the Teacher Info

For Example
A ROW has following data in PERSON TABLE
1 ABC NULL

Now I am Updating the Role as TEACHER in PERSON Table while updating the PERSON Table a new has to be generated with same ID in TEACHER table. But My ID Generate class is identity in person mapping xml file

can any one please help me on this

use ID Generate class as assigned in person mapping xml file