Because standard distinct used on the all fields are very slow and works only with PostgreSQL database
        this method provides alternative to the standard distinct method.
        :return: qs with unique objects

def fast_distinct(self):
        """
        Because standard distinct used on the all fields are very slow and works only with PostgreSQL database
        this method provides alternative to the standard distinct method.
        :return: qs with unique objects
        """
        return self.model.objects.filter(pk__in=self.values_list('pk', flat=True))