场景是这样的：Order下有一个Suppler的集合，即一个订单下可能有多个供应商；Supplier下有一个Product的集合，即对一个供应商采购多个产品。

需求是这样的：算出所有订购产品的总价

模型这样：

public class Order    {        public int OrderId { get; set; }        public ICollection
     
       Suppliers { get; set; }        public Order()        {            Suppliers = new List
      
       ();        }    }    public class Supplier    {        public int SupplierId { get; set; }        public ICollection
       
         Products { get; set; }        public Supplier()        {            Products = new List
        
         ();        }    }    public class Product    {        public int ProductId { get; set; }        public decimal UnitPrice { get; set; }        public int Quantity { get; set; }    }
        
       
      
     

 

这样算出总价：

static void Main(string[] args)        {            var orders = new List
     
                  {                new Order                {                    OrderId = 1,                    Suppliers = new List
      
                           {                        new Supplier {SupplierId=11, Products= new List
       
                                {                            new Product {ProductId=111, Quantity=1, UnitPrice=10 },                            new Product {ProductId = 112, Quantity =1, UnitPrice = 20 }                        } },                        new Supplier {SupplierId =12, Products = new List
        
                                 {                            new Product {ProductId =113, Quantity =2, UnitPrice=30 },                            new Product {ProductId=114, Quantity=1, UnitPrice=50 }                        } }                    }                }            };            var suppliers = orders.Select(t => t.Suppliers);            var productTotalPrice = suppliers.Sum(t => t.Sum(p => p.Products.Sum(o => o.Quantity * o.UnitPrice)));            Console.WriteLine(productTotalPrice);            Console.ReadKey();        }