code: def order_by(self, *fields):
          
          doc = []
          for field in fields:
              if field.startswith('-'):
                  doc.append((field.strip('-'), pymongo.DESCENDING))
              else:
                  doc.append((field, pymongo.ASCENDING))
          return self.sort(doc)
docs: An alternate to ``sort`` which allows you to specify a list
          of fields and use a leading - (minus) to specify DESCENDING.