public function getExportFields()
    {
        $export_fields = Config::inst()->get(
            $this->modelClass,
            self::EXPORT_FIELDS
        );

        if (isset($export_fields) && is_array($export_fields)) {
            $fields = $export_fields;
        } else {
            $fields = parent::getExportFields();
        }

        $this->extend("updateExportFields", $fields);

        return $fields;
    }