code: def check_uniqueness(self, *args, **kwargs):
          
  
          if not self.field.unique:
              return
  
          try:
              pk = self.instance.pk.get()
          except AttributeError:
              pk = None
  
          key = self.get_storage_key(*args)
          value = list(args)[-1]
          pks = self.get_pks_for_filter(key, 'eq', self.normalize_value(value))
  
          self.assert_pks_uniqueness(pks, pk, value)
docs: Check if the given "value" (via `args`) is unique or not.
  
          For the parameters, see ``BaseIndex.check_uniqueness``