linq中let关键字就是对子查询的一个别名，let子句用于在查询中添加一个新的局部变量，使其在后面的查询中可见。

 

linq中let关键字实例

 

1、传统下的子查询与LET关键字的区别

 

 

C# 代码   

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static void Main(string[] args) { int[] numbers = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; //传统下的子查询做法  var query = from num in numbers select num * (from n in numbers where n % 2 == 0 select n).Count(); //使用LET关键字的做法 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、把每个单词开头包含a或者e的找出来

 

 

C# 代码   

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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(' ')//用空格分割成数组   from word in words let w = word.ToLower()//把每个字母小写   where w[0] == 'a' || w[0] == 'e' select word; foreach (var s in query) { Console.WriteLine(s); } Console.ReadLine(); } }

 

3、linq实例3

 

 

C# 代码   

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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实例4

 

 

C# 代码   

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public class Singer { public string Name { set; get; } public int Age { set; get; } } List
        
          list = new List
         
          (){ new Singer{Name="zhangs" ,Age=21}, new Singer{Name="zhangs",Age=25}, new Singer{Name="margy",Age=21} }; var query = from a in list let b = a.Name let c=a.Age where b =="zhangs" & c>21 select a; foreach (var item in query) { Response.Write("姓名: "+item.Name+" 年龄:"+item.Age); } //结果 姓名: zhangs 年龄:25 //使用let 建立了个范围变量，这个范围变量在后续的where子句中使用，如果不使用let子句，where子句的表达式将写成这样： //where a.Name=="zhangs" & a.Age>21