code: def last_change(self):
          
          try:
              cdt = self.latest('created')
              udt = self.latest('updated')
              #print cdt, udt
              return max(cdt.created, udt.updated)
  
          except ObjectDoesNotExist:
              return None
docs: queries the database for the most recent time an object was either created or
          updated
  
          returns datetime or None if db is empty