protected void ddlProducts_SelectedIndexChanged(object sender, EventArgs e)
 {
     ProductService productContext = new ProductService(new BizCustomerOrder());
     object unitPrice = productContext.GetProductPriceByProductID(int.Parse(ddlProducts.SelectedValue));
     if(unitPrice!=null)
     {
         labUnitPrice.Text = unitPrice.ToString();
     }
 }