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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def current_set(self):
 """ A queryset for the active configuration entries only. Only useful if KEY_FIELDS is set. Active means the means recent entries for each unique combination of keys. It does not necessaryily mean enbled. """

        assert self.model.KEY_FIELDS != (), "Just use model.current() if there are no KEY_FIELDS"
        return self.get_queryset().filter(
            pk__in=self._current_ids_subquery()
        ).annotate(
            is_active=models.Value(1, output_field=models.IntegerField())
        )