LinqToSql（一）

最近在看linqtosql，这里就当做笔记本了吧！

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

匿名类型

var data=new {username="冰雪乾坤"，age=18}
console.writeline("username:{0} age:{1}",data.username,data.age);
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

public static calss helper
{
public  static string MDHash(this string s)
{
return system.web.security.formsauthentication.hashPasswordforstoringinconfigfile(s,"md5")
}

public static bool In(this object o,IEnumerable b)
{
foreach(object obj in b)
{
if(obj==o)
{
return true;
}
return false;
}
}
// diaoyong kuozhan
console.writeline("123456".D5Hash());
console.writeline("1".In(new[]{"1","2","3"}));
}

Public calss person
{
public string username{get;protect set;}
public int age{get;set;}
public Person()
{
this.username="冰雪乾坤";
}
}
Person p=new Person();
console.writeline(p.username);

对象初始化器

public class Person
{
public string username{get;set;}
public int age{get;set;}
public override stringToString()
{
return string.Format("username:{0} age{1}",this.username,this.age
}
}


Person p=new Person(){username="qiankun",age=18}
console.writeline(p.tostring());
  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：

l         允许只给一部分属性赋值，包括internal访问级别

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

 public class Person

    {

        public string username { get; set; }

        public int age { get; set; }

        

        public override string  ToString()

        {

        return string.Format("username:{0} age:{1}", this.username, this.age);

        }

} 


var persons =new list<person>{ 
                           new Person{username="q",age=18},
                           new Person{username="a",age=18}
}

foreach(var p in persons)
{
    console.WriteLine(ptostring);
}

var list =new [] {"aa","bb","ac"};
var resoult = Array.FindAll(list,s=>(s.IndexOf("a")>-1));

foreach(var v in result)
{
       Console.WriteLine(v);
}

 public delegate int mydog(int a,int b);

 public static class LambdaTest
 { 
       public static int opr(this int a,int b,mydg dg)
        {
            return dg(a,b);
        }
 }


Console.WriteLine(1.oper(2,(a,b)=>a+b));
Console.WriteLine(2.oper(1,(a,b)=>a+b));

var persons=new List<Person>{
      new Person{username="A",age=18},
      new Person {username="B",age=20},
      new Person {username="C",age=22}
};
 
var selectperson =from p in persons
                           where p.age>=21
                           select p.username.ToUpper();
foreach(var p in selectperson)
{
    console.writeLine(p);
}

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