public BillItem findBillItem(int billId, int medicineId) {
        String query = "SELECT `billItem`.`billId`, "
                + "         `billItem`.`medicineId`, "
                + "         `billItem`.`quantity` "
                + "     FROM `billItem` "
                + "     WHERE `billItem`.`billId` = '%d'"
                + "     AND `billItem`.`medicineId` = '%d';";
        DBA dba = Helper.getDBA();
        try {
            ResultSet rs = dba.executeQuery(String.format(query, billId, medicineId));

            while (rs.next()) {
                this.billId = rs.getInt("billId");
                this.medicineId = rs.getInt("medicineId");
                this.quanitity = rs.getInt("quantity");
            }
            rs.close();
            dba.closeConnections();

        } catch (SQLException sqlEx) {
            dba.closeConnections();
            Helper.logException(sqlEx);
        }
        return this;
    }