高效的LINQ語句(三)

Model層的類如下:

public class Order
    {
        public int Id { get; set; }
        public decimal Amount { get; set; }
        public string CustomerName { get; set; }
        public string Status { get; set; }
    }           

public  class Person
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }           

Program.cs代碼如下:

class Program
    {
       //通俗的來講隻有等autorevent.Set()成功運作後,autorevent.WaitOne()才能夠獲得運作機會;Set是發信号，WaitOne是等待信号，隻有發了信号，等待的才會執行。如果不發的話，WaitOne後面的程式就永遠不會執行。
        private static AutoResetEvent autorevent= new AutoResetEvent(false);

        private static List<Person> list = new List<Person>()
        {
            new Person() {Name = "羅斯", Age = 19},
            new Person() {Name = "斯蒂夫", Age = 35},
            new Person() {Name = "傑西卡", Age = 30},
        };


        private static void Main(string[] args)
        {
            //CheckOrders();
            //Common();
            //RemoveFromList();
            //ExceptionHandling();
            //-----------------------------------------------------------------
            //--------------------------------mock 非線程 safe----------------------------

            Thread t1 = new Thread(() =>
            {
                //確定等待t2開始之後才運作下面的代碼
                autorevent.WaitOne();
                foreach (var item in list)
                {
                    Console.WriteLine("t1:" + item.Name);
                    Thread.Sleep(1000);
                }
            });
            t1.Start();
            Thread t2 = new Thread(() =>
            {
                //通知t1可以執行代碼
                autorevent.Set();
                //沉睡1秒是為了確定删除操作在t1的疊代過程中
                Thread.Sleep(1000);
                list.RemoveAt(2);
            });
            t2.Start();

            Console.ReadKey();
        }

        public static void CheckOrders()
        {
            List<Order> orders = new List<Order>()
            {
	            new Order { Id = 123, Amount = 29.95m, CustomerName = "馬克", Status = "Delivered" },
	            new Order { Id = 456, Amount = 45.00m, CustomerName = "斯蒂芬", Status = "Refunded" },
	            new Order { Id = 768, Amount = 32.50m, CustomerName = "克萊爾", Status = "Delivered" },
            };

            bool anyRefunded = orders.Any(o => o.Status == "Refunded");
            if (anyRefunded)
            {
                Console.WriteLine("有退款訂單");
            }
            else
            {
                Console.WriteLine("沒有退款訂單");
            }

            bool allDelivered = orders.All(o => o.Status == "Delivered");
            if (allDelivered)
            {
                Console.WriteLine("都已發貨");
            }
            else
            {
                Console.WriteLine("未全部都已發貨");
            }
        }

        public static void Common()
        {
            var daysToChristmas = (new DateTime(DateTime.Today.Year, 12, 25) - DateTime.Today).TotalDays;
            Console.WriteLine(daysToChristmas);

            //-----------------------------------------------------------------
            int SUM = "10,5,0,8,10,1,4,0,10,1"
                .Split(',')
                .Select(int.Parse)
                .OrderBy(n => n)
                .Skip(3)
                .Sum();
            Console.WriteLine(SUM);
            //-----------------------------------------------------------------
            var customers = new[] {
	            new { Name = "安妮", Email = "" },
	            new { Name = "本", Email = "" },
	            new { Name = "莉莉", Email = "" },
	            new { Name = "嬌兒", Email = "" },
	            new { Name = "桑木", Email = "" },
            };
            foreach (var customer in
                from c in customers
                where !String.IsNullOrEmpty(c.Email)
                select c)
            {
                Console.WriteLine("發送郵件給 {0}", customer.Name);
            }
            //效果同上
            foreach (var customer in customers.Where(c => !String.IsNullOrEmpty(c.Email)))
            {
                Console.WriteLine("發送郵件給 {0}", customer.Name);
            }
        }

        public static void RemoveFromList()
        {
            Func<List<string>> makeList = () => Enumerable.Range(1, 10000000).Select(n => ("Item " + n + "")).ToList();
            var itemsToRemove = new[] { "Item 0", "Item 1", "Item 50", "Item 1000", "Item 999999", "Item 9999999" };
            var stopwatch = new Stopwatch();
            var list = makeList();

            stopwatch.Start();
            foreach (var item in itemsToRemove)
            {
                list.Remove(item);
            }
            stopwatch.Stop();

            Console.WriteLine(list.Count + "Foreach 花了 {0}ms", stopwatch.ElapsedMilliseconds);

            list = makeList();


            stopwatch.Restart();
            var newList = list.Except(itemsToRemove).ToList(); //效率極低
            stopwatch.Stop();

            Console.WriteLine(newList.Count + "Except 花了 {0}ms", stopwatch.ElapsedMilliseconds);
        }


        public static void ExceptionHandling()
        {
            var numbers = Enumerable.Range(1, 10)
                    .Select(n => 5 - n)
                    .Select(n =>
                    {
                        try
                        {
                            return 10 / n;
                        }
                        catch (Exception e)
                        {
                            Console.WriteLine("拉姆達錯誤: " + e.Message);
                            return -1;
                        }
                    });

            foreach (var n in numbers)
            {
                Console.WriteLine(n);
            }
        }

    }