public ProductBusiness()
 {
     _productRepository            = new ProductRepository();
     _purchaseBillDetailRepository = new PurchaseBillDetailRepository();
     _saleBillDetailRepository     = new SaleBillDetailRepository();
 }
 public PurchaseBillBusiness()
 {
     _purchaseBillRepository       = new PurchaseBillRepository();
     _purchaseBillDetailRepository = new PurchaseBillDetailRepository();
 }