code: def lookup_field_orderable(self, field):
          
          try:
              self.model._meta.get_field_by_name(field)
              return True
          except Exception:
              # that field doesn't exist, so not sortable
              return False
docs: Returns whether the passed in field is sortable or not, by default all 'raw' fields, that
          is fields that are part of the model are sortable.