class AdManager(models.Manager):
    def _get_model(self, category):
        try:
            return [m for m in self.model.__subclasses__() if m.__name__ == category.ad_class][0]
        except Exception as e:
            raise ModelNotFound(category, traceback.format_exc())

    def get_models(self, category):
        admodels = []
        if category:
            if category.is_endpoint:
                admodels = [self._get_model(category)]
            else:
                for c in category.get_descendants().filter(is_endpoint=True):
                    admodels.append(self._get_model(c))
        else:
            for c in Category.objects.filter(is_endpoint=True):
                admodels.append(self._get_model(c))
        return admodels

    def _get_filter_params(self, city, options, query):
        params = {'city__exact': city.pk}
        q = query.get('q')[0] if query.get('q') else None
        if q:
            params.update({'description__contains': q})
        params.update(dict(BaseOption.get_adoptions_classes(c).get_queryset_lookup(v) for c, v in options.items()))
        return params

    def list(self, category, city, options, query):
        params = self._get_filter_params(city, options, query)
        admodels = self.get_models(category)

        if len(admodels) == 1:
            result_qs = admodels[0].filter(**params)
        else:
            related_names = [m.__name__.lower() for m in admodels]
            result_qs = self.model.objects.select_related(*related_names).filter(**params)
        return result_qs