def currently_active(self, when=None):
        """Filter on start and end dates to limit to currently active postitions"""

        if when == None:
            when = datetime.date.today()

        now_approx = repr(ApproximateDate(year=when.year, month=when.month, day=when.day))

        qs = (
            self
                .filter(start_date__lte=now_approx)
                .filter(Q(sorting_end_date_high__gte=now_approx) | Q(end_date=''))
        )

        return qs