高效的LINQ语句(三)

Model层的类如下:

  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代码如下:

 class Program
    {
        //AutoResetEvent 允许线程通过发信号互相通信。通常，此通信涉及线程需要独占访问的资源。
        //线程通过调用 AutoResetEvent 上的 WaitOne 来等待信号。如果 AutoResetEvent 处于非终止状态，则该线程阻塞，并等待当前控制资源的线程,通过调用 Set 发出资源可用的信号。
        //调用 Set 向 AutoResetEvent 发信号以释放等待线程。AutoResetEvent 将保持终止状态，直到一个正在等待的线程被释放，然后自动返回非终止状态。如果没有任何线程在等待，则状态将无限期地保持为终止状态。
        //可以通过将一个布尔值传递给构造函数来控制 AutoResetEvent 的初始状态，如果初始状态为终止状态，则为 true；否则为 false。

        //通俗的来讲只有等myResetEven.Set()成功运行后,myResetEven.WaitOne()才能够获得运行机会;Set是发信号，WaitOne是等待信号，只有发了信号，等待的才会执行。如果不发的话，WaitOne后面的程序就永远不会执行。
        private static AutoResetEvent autoSet = new AutoResetEvent(false);


        private static List<Person> list = new List<Person>()
        {
            new Person() {Name = "Rose", Age = 19},
            new Person() {Name = "Steve", Age = 45},
            new Person() {Name = "Jessica", Age = 20},
        };


        private static void Main(string[] args)
        {
            //CheckOrders();
            //Common();
            //RemoveFromList();
            //ExceptionHandling();
            //-----------------------------------------------------------------
            //--------------------------------模拟非线程安全----------------------------

            Thread t1 = new Thread(() =>
            {
                //确保等待t2开始之后才运行下面的代码
                autoSet.WaitOne();
                foreach (var item in list)
                {
                    Console.WriteLine("t1:" + item.Name);
                    Thread.Sleep(1000);
                }
            });
            t1.Start();
            Thread t2 = new Thread(() =>
            {
                //通知t1可以执行代码
                autoSet.Set();
                //沉睡1秒是为了确保删除操作在t1的迭代过程中
                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 = "Mark", Status = "Delivered" },
	            new Order { Id = 456, Amount = 45.00m, CustomerName = "Steph", Status = "Refunded" },
	            new Order { Id = 768, Amount = 32.50m, CustomerName = "Claire", Status = "Delivered" },
            };

            bool anyRefunded = orders.Any(o => o.Status == "Refunded");
            if (anyRefunded)
            {
                Console.WriteLine("There are refunded orders");
            }
            else
            {
                Console.WriteLine("No refunds");
            }

            bool allDelivered = orders.All(o => o.Status == "Delivered");
            if (allDelivered)
            {
                Console.WriteLine("Everything was delivered");
            }
            else
            {
                Console.WriteLine("Not everything was delivered");
            }
        }

        public static void Common()
        {
            //距离圣诞节的天数
            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 = "Annie", Email = "annie@test.com" },
	            new { Name = "Ben", Email = "" },
	            new { Name = "Lily", Email = "lily@test.com" },
	            new { Name = "Joel", Email = "joel@test.com" },
	            new { Name = "Sam", Email = "" },
            };
            foreach (var customer in
                from c in customers
                where !String.IsNullOrEmpty(c.Email)
                select c)
            {
                Console.WriteLine("Sending email to {0}", customer.Name);
            }
            //效果同上
            foreach (var customer in customers.Where(c => !String.IsNullOrEmpty(c.Email)))
            {
                Console.WriteLine("Sending email to {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 took {0}ms", stopwatch.ElapsedMilliseconds);

            list = makeList();


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

            Console.WriteLine(newList.Count + "Except took {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("Error in lambda: " + e.Message);
                            return -1;
                        }
                    });

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

    }