def save(self, filename=None):
        filename = Path(filename) if filename is not None else self.filename
        with filename.open("w") as f:
            f.write(self.yaml)
def index(self, request):
        queryset = Condition.objects.select_related('source', 'target_option')
        serializer = ConditionIndexSerializer(queryset, many=True)
        return Response(serializer.data)