code: def create_model(cls, name, field=None):
          
          if field:
              attrs = {'name': name, 'field': field}
          else:
              attrs = {'name': name, 'field': {'_id': ObjectId()}}
  
          return type(str(name), (cls, ), attrs)()
docs: dynamic create new model
          :args field table field, if field is None or {}, this model can not use create method