class CustomTripFilter(filters.Filter):
    def filter(self, qs, value):
        if value in EMPTY_VALUES:
            return qs

        try:
            value = int(value)
        except ValueError:
            raise ValidationError('Trip filter must be integer.')

        trip = Trip.objects.get(pk=value)

        qs = qs.filter(vehicle_id=trip.vehicle_id)

        if trip.start_location is None:
            raise ValidationError('Trip is not valid.')

        qs = qs.filter(pk__gte=trip.start_location.pk)

        if trip.end_location is not None:
            qs = qs.filter(pk__lte=trip.end_location.pk)

        return qs