public function get_voucher_codes( $format = 'OBJECT' ) {

		global $wpdb;

		$table          = $this->get_codes_table_name();
		$redeemed_table = $this->get_redemptions_table_name();

		$query = "SELECT c.*, count(r.id) as used
                  FROM $table as c
                  LEFT JOIN $redeemed_table as r
                  ON c.`id` = r.`code_id`
                  WHERE `voucher_id` = $this->id AND `is_deleted` = 0
                  GROUP BY c.id";
		return $wpdb->get_results( $query, $format );
	}