LINQ查询操作符

    #region Types

    public enum Countries
    {
        USA,
        Italy,
    }

    public class Customer
    {
        public string Name {get;set;}
        public string City { get; set; }
        public Countries Country { get; set; }
        public Order[] Orders { get; set; }

        public override string ToString()
        {
            return String.Format("Name: {0} - City: {1} - Country: {2}",
                this.Name, this.City, this.Country);
        }
    }

    public class Order
    {
        public int IdOrder { get; set; }
        public int Quantity { get; set; }
        public bool Shipped { get; set; }
        public string Month { get; set; }
        public int IdProduct { get; set; }

        public override string ToString()
        {
            return String.Format("IdOrder: {0} - IdProduct: {1} - Quantity: {2} - Shipped: {3} - Month: {4}",
                this.IdOrder, this.IdProduct, this.Quantity, this.Shipped, this.Month);
        }
    }

    public class Product
    {
        public int IdProduct { get; set; }
        public decimal Price { get; set; }

        public override string ToString()
        {
            return String.Format("IdProduct: {0} - Price: {1}", this.IdProduct, this.Price);
        }
    }

    #endregion

    class Program
    {
        private static Customer[] customers;
        private static Product[] products;

        static void LoadData()
        {
            customers = new Customer[] {
                new Customer {Name = "Paolo", City = "Brescia", Country = Countries.Italy, Orders = new Order[] {
                    new Order {IdOrder = 1, Quantity = 3, IdProduct = 1, Shipped = false, Month = "January"},
                    new Order {IdOrder = 2, Quantity = 5, IdProduct = 2, Shipped = true, Month = "May"}}},
                new Customer {Name = "Marco", City = "Torino", Country = Countries.Italy, Orders =  new Order[] {
                    new Order {IdOrder = 3, Quantity = 10, IdProduct = 1, Shipped = false, Month = "July"},
                    new Order {IdOrder = 4, Quantity = 20, IdProduct = 3, Shipped = true, Month = "December"}}},
                new Customer {Name = "James", City = "Dallas", Country = Countries.USA, Orders =  new Order[] {
                    new Order {IdOrder = 5, Quantity = 20, IdProduct = 3, Shipped = true, Month = "December"}}},
                new Customer {Name = "Frank", City = "Seattle", Country = Countries.USA, Orders =  new Order[] {
                    new Order {IdOrder = 6, Quantity = 20, IdProduct = 5, Shipped = false, Month = "July"}}}};

            products = new Product[] {
                new Product {IdProduct = 1, Price = 10 },
                new Product {IdProduct = 2, Price = 20 },
                new Product {IdProduct = 3, Price = 30 },
                new Product {IdProduct = 4, Price = 40 },
                new Product {IdProduct = 5, Price = 50 },
                new Product {IdProduct = 6, Price = 60 }};
        }

        static Program()
        {
            LoadData();
        }
        static void Main(string[] args)
        {
           // restrictionOperatorWithIndex();

           // projectionWithIndex();
            //selectManySample();
            selectManySampleWithCustomSelector();
        }

        //使用分页的Where
        static void restrictionOperatorWithIndex()
        {
            var expr = customers
                .Where((c, index) => (c.Country == Countries.Italy && index >= 1))
                .Select(c => new { c.Name });

            foreach (var item in expr)
            {
                Console.WriteLine(item);
            }
        }

        //使用分页的Select
        static void projectionWithIndex()
        {
            var expr =
                customers
                .Select((c, index) => new { index, c.Name, c.Country });

            foreach (var item in expr)
            {
                Console.WriteLine(item);
            }
        }

        //SelectMany
        static void selectManySample()
        {
            var orders = customers
                .Where(c => c.Country == Countries.Italy)
                .SelectMany(c =>c.Orders);

            //查询表达式
            //var orders = from c in customers
            //             where c.Country == Countries.Italy
            //             from o in c.Orders
            //             select o;
            foreach (var item in orders)
            {
                Console.WriteLine(item);
            }
        }


        static void selectManySampleWithCustomSelector()
        {
            var items = customers
                .Where(c => c.Country == Countries.Italy)
                .SelectMany(c => c.Orders, (c, o) => new { o.Quantity, o.IdProduct });

            //查询表达式
            //var items = from c in customers
            //            where c.Country == Countries.Italy
            //            from o in c.Orders
            //            select new { o.Quantity, o.IdProduct };
            foreach (var item in items)
            {
                Console.WriteLine(item);
            }
        }

    }