code: def query_insert(self, direction='max'):
          
          if direction == 'min':
              return Layer.objects.aggregate(
                  Min('last_updated'))['last_updated__min'].strftime('%Y-%m-%dT%H:%M:%SZ')
          return self._get_repo_filter(Layer.objects).aggregate(
              Max('last_updated'))['last_updated__max'].strftime('%Y-%m-%dT%H:%M:%SZ')
docs: Query to get latest (default) or earliest update to repository