public void addProductVisibleDiscount(int product, int session, double percentage, string duration) { if (percentage <= 0 || percentage >= 1) { throw new IllegalAmountException("percentage of discount must be a number between 0 to 1"); } if (product < 0) { throw new ILLArgumentException("illegal product number"); } if (session < 0) { throw new NullReferenceException("session is a null reference"); } db.addProductVisibleDiscount(product, percentage, duration, session); }