/**
  * Retrieve a logistician by ID.
  * @param int|string $id
  * @return Logistician
  */
 public function get_logistician_by_id($id)
 {
     $logistician = new ModelTemplate('Logistician');
     $logistician = $logistician->get_single('id', $id);
     if ($logistician) {
         // Add super class SMSUser fields to the Logistician instance.
         $smsUserCtr = new SMSUser_Controller();
         // It should have super class fields, otherwise delete the instance.
         if ($smsUser = $smsUserCtr->get_smsuser_by_id($id)) {
             $logistician->add_field('telephone', $smsUser->telephone);
         } else {
             $logistician = null;
         }
     }
     return $logistician;
 }
 /**
  * Retrieve single truck driver, specified by ID.
  * @param int|string $id
  * @return TruckDriver
  */
 public function get_truck_driver_by_id($id)
 {
     $truckDriver = new ModelTemplate('TruckDriver');
     $truckDriver = $truckDriver->get_single('id', $id);
     if ($truckDriver) {
         // Add super class SMSUser fields to the TruckDriver instance.
         $smsUserCtr = new SMSUser_Controller();
         // It should have super class fields, otherwise delete the instance.
         if ($smsUser = $smsUserCtr->get_smsuser_by_id($id)) {
             $truckDriver->add_field('telephone', $smsUser->telephone);
         } else {
             $truckDriver = null;
         }
     }
     return $truckDriver;
 }