public void Write(Product product)
 {
     using (PointOfSaleContext context = new PointOfSaleContext())
     {
         context.Products.AddOrUpdate(product);
         context.SaveChanges();
     }
 }
        public void DeleteByProductCode(int productCode)
        {
            using (PointOfSaleContext context = new PointOfSaleContext())
            {
                Product product = (from p in context.Products
                                   where p.ProductCode == productCode
                                   select p).FirstOrDefault();

                if (product != null)
                {
                    context.Products.Remove(product);
                    context.SaveChanges();
                }
            }
        }