product_obj = products.all()[0]
db.session.expunge(product_obj) # expunge the object from session
make_transient(product_obj) # http://docs.sqlalchemy.org/en/rel_1_1/orm/session_api.html#sqlalchemy.orm.session.make_transient
product_obj.product_uid = 'something'
db.session.add(product_obj)