LinqToSql（一）

最近在看linqtosql，这里就当做笔记本了吧！

隐含类型局部变量

1 先介绍隐含类型局部变量
2 var age=18;
3 var username="冰雪乾坤";
4 var userlist=new[] {"a","b","c"}
5 foreach(var user in userlist)
6 {
7 console.writeline(user);
8 }

匿名类型

1 var data=new {username="冰雪乾坤"，age=18}
2 console.writeline("username:{0} age:{1}",data.username,data.age);
3 这里的var 是懒人类型，我们不需要管他是什么类型，他将会自我匹配

扩展方法

 1 public static calss helper
 2 {
 3 public  static string MDHash(this string s)
 4 {
 5 return system.web.security.formsauthentication.hashPasswordforstoringinconfigfile(s,"md5")
 6 }
 7 
 8 public static bool In(this object o,IEnumerable b)
 9 {
10 foreach(object obj in b)
11 {
12 if(obj==o)
13 {
14 return true;
15 }
16 return false;
17 }
18 }
19 // diaoyong kuozhan
20 console.writeline("123456".D5Hash());
21 console.writeline("1".In(new[]{"1","2","3"}));
22 }

 1 Public calss person
 2 {
 3 public string username{get;protect set;}
 4 public int age{get;set;}
 5 public Person()
 6 {
 7 this.username="冰雪乾坤";
 8 }
 9 }
10 Person p=new Person();
11 console.writeline(p.username);

对象初始化器

 1 public class Person
 2 {
 3 public string username{get;set;}
 4 public int age{get;set;}
 5 public override stringToString()
 6 {
 7 return string.Format("username:{0} age{1}",this.username,this.age
 8 }
 9 }
10 
11 
12 Person p=new Person(){username="qiankun",age=18}
13 console.writeline(p.tostring());
14   编译器会自动为你做setter操作，使得原本几行的属性赋值操作能在一行中完成。这里需要注意：
15 
16 l         允许只给一部分属性赋值，包括internal访问级别
17 
18 l         可以结合构造函数一起使用，并且构造函数初始化先于对象初始化器执行

list init

 1  public class Person
 2 
 3     {
 4 
 5         public string username { get; set; }
 6 
 7         public int age { get; set; }
 8 
 9         
10 
11         public override string  ToString()
12 
13         {
14 
15         return string.Format("username:{0} age:{1}", this.username, this.age);
16 
17         }
18 
19 } 
20 
21 
22 var persons =new list<person>{ 
23                            new Person{username="q",age=18},
24                            new Person{username="a",age=18}
25 }
26 
27 foreach(var p in persons)
28 {
29     console.WriteLine(ptostring);
30 }

Lambda表达式

1 var list =new [] {"aa","bb","ac"};
2 var resoult = Array.FindAll(list,s=>(s.IndexOf("a")>-1));
3 
4 foreach(var v in result)
5 {
6        Console.WriteLine(v);
7 }

复杂的例子

 1  public delegate int mydog(int a,int b);
 2 
 3  public static class LambdaTest
 4  { 
 5        public static int opr(this int a,int b,mydg dg)
 6         {
 7             return dg(a,b);
 8         }
 9  }
10 
11 
12 Console.WriteLine(1.oper(2,(a,b)=>a+b));
13 Console.WriteLine(2.oper(1,(a,b)=>a+b));

查询

 1 var persons=new List<Person>{
 2       new Person{username="A",age=18},
 3       new Person {username="B",age=20},
 4       new Person {username="C",age=22}
 5 };
 6  
 7 var selectperson =from p in persons
 8                            where p.age>=21
 9                            select p.username.ToUpper();
10 foreach(var p in selectperson)
11 {
12     console.writeLine(p);
13 }

等价于
var selectperson=persons.where(p=>p.age>=21).select(p=>p.username.ToUpper());