I have a mapping class which specifies a mapping relationship which looks like this:

<set name="groups" table="group_permission" order-by="updated">
<key column="permission_id"/>
<many-to-many column="group_id" class="Group"/>
</set>

The updated column is on the many-to-many join table group_permission. When I use hbm2ddl.auto to create the schema automatically obviously it has no way to know what the udpated column is and doesn't create it. Is there a way to make hbm2ddl.auto to create such meta columns on many-to-many SQL tables? If not then is there a way to do this manually in hibernate - corresponding to the SQL statement "alter table group_permission add column updated timestamp default now() on update now();"