mORMot Open Source

Hi,
I'm a newbie with Momrmot :
1. If the database already exist do I need to write manualy in lazarus each class to map or do Mormot can reflect the database existing schema (and may be write somewhere this class for me) ?
2. I understand it's not the best way to get a lot of joins and it will  be preferable to update table with json collections but how to synchronize such collections if I delete a records without cascading with the database ?
Thank to your response.
Patrick