Object Relational Mapping (ORM) using NHibernate - Part 7 of 8 Completing the Ecommerce Example

using System;
using Iesi.Collections.Generic;

namespace ECommerceSystem.Domain
{
    class OrderNumberHelper
    {
        public static string GenerateOrderNumber()
        {
            // GetTodaysDate and make orderno from it
            //by concatenating orderno with it

            orderNo++;
            return ((DateTime.Now.ToShortDateString()).Replace("/","")+orderNo.ToString());
        }
        private static int orderNo;
    }
    public class Order
    {
        public Order() 
        {
            OrderNumber = OrderNumberHelper.GenerateOrderNumber();
            OrderItems = new HashedSet<Item>();
            NotAvailableItemDescriptions = new System.Collections.Generic.List<ProductDescription>();
        }
        public Order(bool is_fast_shipping)
        {
            OrderNumber = OrderNumberHelper.GenerateOrderNumber();
            OrderItems = new HashedSet<Item>();
            IsFastShipping = true;
            NotAvailableItemDescriptions = new System.Collections.Generic.List<ProductDescription>();
        }

        public virtual long OrderId { get; set; }

        public virtual string OrderNumber { get; set; }

        public virtual ISet<Item> OrderItems { get; set; }

        public virtual Customer OrderedByCustomer { get; set; }

        public virtual double ShippingCharges { get; set; }

        public virtual double OrderCost { get; set; }

        //Order page data

        public virtual bool IsFastShipping { get; set; }

        //Order page data

        public virtual bool IsGiftWrapped { get; set; }

        public virtual System.Collections.Generic.IList<ProductDescription> NotAvailableItemDescriptions { get; set; }
      
    }
}