linq中let關鍵字學習

linq中let關鍵字就是對子查詢的一個別名，let子句用于在查詢中添加一個新的局部變量，使其在后面的查詢中可見。

linq中let關鍵字實例

1、傳統下的子查詢與LET關鍵字的區別

static void Main(string[] args){    int[] numbers = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };     //傳統下的子查詢做法    var query = from num in numbers                select num * (from n in numbers                              where n % 2 == 0                              select n).Count();     //使用LET關鍵字的做法    var query = from num in numbers          let evenNumbers = from n in numbers                             where n % 2 == 0                              select n           select num * evenNumbers.Count();     foreach (var item in query)    {        Console.WriteLine(item);    }     Console.Read(); } 

2、把每個單詞開頭包含a或者e的找出來

using System;using System.Linq;public class Test{    static void Main(string[] args)    {        string[] strings = { "A penny saved is a penny earned.", "The aaxly sdj", "the pa is no" };        var query = from sentence in strings                    let Words = sentence.Split(' ')//用空格分割成數組                                    from word in words                    let w = word.ToLower()//把每個字母小寫                            where w[0] == 'a' || w[0] == 'e'                    select word;        foreach (var s in query)        {            Console.WriteLine(s);        }        Console.ReadLine();    }}

3、linq實例3

var query = from p in persons            let friendlyName = p.Gender == "男" ? "Mr" : "Ms" + p.Name            select new            {                UserID = p.ID,                FriendName = friendlyName            };foreach (var item in query){    Console.WriteLine("No:{0},Friendly Name:{1}", item.UserID, item.FriendName);}

4、linq實例4

public class Singer    {        public string Name { set; get; }