public function set_campus($campus) {
        $campus = !is_array($campus) ? array($campus) : $campus;

        $this->_campus = array();
        foreach ($campus as $c) {
            $c = strtolower($c);
            if (!in_array($c, array('canterbury', 'medway'))) {
                throw new \Exception("Invalid campus: '{$campus}'.");
            }

            $this->_campus[] = $c;
        }
    }