Linq学习笔记

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);
            }
        }
    }
}

自己的数据表结构：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace test
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            linq1();
            linq2();
        }
        /// <summary>
        /// 熟悉linq语法，声明变量跟js一样，属于弱类型
        /// </summary>
        protected void linq1()
        {
            var userList = new[] {'a','b','c' };
            foreach (var user in userList)
            {
                MessageBox.Show(user.ToString());
            }
        }
        protected void linq2()
        {
            NorthwindDataContext datacontext = new NorthwindDataContext(@"Data Source=.\SQLEXPRESS;AttachDbFilename='c:\documents and settings\administrator\my documents\visual studio 2010\Projects\test\test\test.mdf';Integrated Security=True;User Instance=True");
            studentInfo st = new studentInfo();
            //执行普通的sql语句
            IEnumerable<studentInfo> studentinfos = datacontext.ExecuteQuery<studentInfo>("select * from studentInfo");
            st = studentinfos.First();
            MessageBox.Show(st.studentid.ToString());
            //单条记录查询
            var cus = from c in datacontext.studentInfo where c.studentid.Equals(1) select c;
            st = cus.First();
            MessageBox.Show(st.studentid.ToString());
            //查询结果集
            IEnumerable<studentInfo> studentinfos1= from dust in datacontext.studentInfo where dust.studentid != 1 orderby dust.studentAge descending select dust;
            st = studentinfos1.Last();
        }
    }
}