高效的LINQ语句有哪些

小编给大家分享一下高效的LINQ语句有哪些，相信大部分人都还不怎么了解，因此分享这篇文章给大家参考一下，希望大家阅读完这篇文章后大有收获，下面让我们一起去了解一下吧！

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 list = new List()        {            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 orders = new List()            {                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> 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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