I am pretty sure SQLAlchemy will translate that into: UPDATE purchase SET downloads_left=%(downloads_left)s WHERE purchase.id = %(purchases_id)s; By the w

I am pretty sure SQLAlchemy will translate that into: UPDATE purchase SET downloads_left=%(downloads_left)s WHERE purchase.id = %(purchases_id)s; By the way, the posted code has an off-by-one error, as it should do the checking first before the minus operation. Also, the line `db.session.add(purchase)` is redundant. EDIT: remove bad sample