Linq学习笔记二(Linq to sql 增删改查)

1.接上篇http://www.cnblogs.com/greatverve/archive/2010/05/12/1733513.html
在Northwind下新建表t_User
ID,             int,主键，自增。
UserName,  varchar(50)
Pwd,           varchar(50)

2.从服务器资源管理器中把t_User拖到Northwind.dbml中。
即生成orm映射。

3.增删改查的代码参考下面的Linq3();

代码

using  System;
using  System.Collections.Generic;
using  System.Linq;
using  System.Web;
using  System.Web.UI;
using  System.Web.UI.WebControls;

using  System.Data.Common;
using  System.Collections.Generic;

namespace  FirstLinq
{
     public   partial   class  _Default : System.Web.UI.Page
    {
        NorthwindDataContext ctx  =   new  NorthwindDataContext( " Data Source=ZHANGSHUQIANG;Initial Catalog=Northwind;Persist Security Info=True;User ID=sa;Password=sa " );
         protected   void  Page_Load( object  sender, EventArgs e)
        {
            Linq1();
            Linq2();
            Linq3();
        }
         ///   <summary>
         ///  增删改查
         ///   </summary>
         private   void  Linq3()
        {
             // 增
            t_User user  =   new  t_User();
            user.UserName  =   " 大气象 " ;
            user.Pwd  =   " 123456 " ;
            ctx.t_User.InsertOnSubmit(user); // 以前的方法是Add();
            ctx.SubmitChanges();

             // 改
             // 参考这样的语法string s = (from a in ctx.Customers select a).Single(a => a.ID == 2);
            t_User userUpdate  =  ctx.t_User.SingleOrDefault(t_User  =>  t_User.ID  ==   2 ); // Single与SingleOrDefault没区别
            userUpdate.UserName  =   " 大气象1 " ;
            ctx.SubmitChanges();

             // 删
            t_User userDelete  =  (from userinfo  in  ctx.t_User  where  userinfo.ID  ==   1  select userinfo).FirstOrDefault();
             if  (userDelete  !=   null )
            {
                ctx.t_User.DeleteOnSubmit(userDelete);
                ctx.SubmitChanges();
            }
        }
         ///   <summary>
         ///  熟悉Linq to sql语法
         ///   </summary>
         private   void  Linq2()
        {
            Customers customer  =   new  Customers();

             // 执行普通的sql语句，查询CustomerID="ANATR"的记录
            IEnumerable < Customers >  customers  =  ctx.ExecuteQuery < Customers > ( " select * from Customers where CustomerID='ANATR' " );
            customer  =  customers.First();
            Response.Write(customer.CustomerID);

             // 使用Linq查询单条记录
            var cus  =  from c  in  ctx.Customers  where  c.CustomerID.Equals( " ANATR " ) select c;
            customer  =  cus.First();
            Response.Write(customer.CompanyName);

             // 查询结果集，语法：from 临时表名 in 表集合 orderby 临时表名.字段名 升级序 select 临时表名
            gdvCustomers.DataSource  =  from cust  in  ctx.Customers  where  cust.CustomerID  !=   " ANATR "  orderby cust.CompanyName descending select cust;
            gdvCustomers.DataBind();
        }
         ///   <summary>
         ///  熟悉一下linq语法，变量的定义类似js，无须声明类型。
         ///   </summary>
         private   void  Linq1()
        {
            var age  =   29 ;
            var username  =   " greatverve " ;
            var userlist  =   new [] {  " a " ,  " b " ,  " c "  };
             foreach  (var user  in  userlist)
            {
                Response.Write(user);
            }
        }
    }
}

 

 

参考：
http://www.cnblogs.com/webabcd/archive/2007/10/18/928353.html
http://www.cnblogs.com/lovecherry/archive/2007/08/16/858009.html