public function get_custom_user_profile_fields() {
        global $DB;
        // If already retrieved then return.
        if (!is_null($this->customfields)) {
            return $this->customfields;
        }

        $this->customfields = array();
        if ($proffields = $DB->get_records('user_info_field')) {
            foreach ($proffields as $proffield) {
                $this->customfields[] = 'profile_field_'.$proffield->shortname;
            }
        }
        unset($proffields);

        return $this->customfields;
    }