linq中l(wèi)et關(guān)鍵字學(xué)習(xí)

linq中l(wèi)et關(guān)鍵字就是對(duì)子查詢的一個(gè)別名，let子句用于在查詢中添加一個(gè)新的局部變量，使其在后面的查詢中可見(jiàn)。

linq中l(wèi)et關(guān)鍵字實(shí)例

1、傳統(tǒng)下的子查詢與LET關(guān)鍵字的區(qū)別

static void Main(string[] args){    int[] numbers = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };     //傳統(tǒng)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(guān)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(gè)單詞開(kāi)頭包含a或者e的找出來(lái)

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(shù)組                                    from word in words                    let w = word.ToLower()//把每個(gè)字母小寫(xiě)                            where w[0] == 'a' || w[0] == 'e'                    select word;        foreach (var s in query)        {            Console.WriteLine(s);        }        Console.ReadLine();    }}

3、linq實(shí)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(shí)例4

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