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分享一些高效的LINQ语句代码Model层的类如下:Program.cs代码如下:

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 = [email protected] },
                new { Name = Ben, Email =  },
                new { Name = Lily, Email = [email protected] },
                new { Name = Joel, Email = [email protected] },
                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);
            }
        }

    }

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