public function sortByZoneType()
    {
        return $this->sort(function (Zone $zone1, Zone $zone2) {
            $zone1Order = $zone1->getZoneType()->getOrder();
            $zone2Order = $zone2->getZoneType()->getOrder();

            // implement alpha sort on name if equal ?

            return $zone1Order >= $zone2Order ? 1 : -1;
        });
    }