LINQ to SQL的快速入门例子

这也是今天课堂上的一个简单例子，演示了如何使用LINQ to SQL的技术，以及C# 3的一些新特性

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace LINQtoSQLSample
{
class Program
{
static void Main(string[] args)
{
//利用LINQ TO SQL实现快捷高效的数据库访问
//0.准备：创建DataContext对象
TraceModelDataContext context = new TraceModelDataContext();
context.Log = Console.Out;

//var context2 = new TraceModelDataContext();
//C# 3的新语法，var关键字是表示类型推断

//var context3 = new TraceModelDataContext("server=(local);database=db;integrated security=true");
//如果生产服务器上面的数据库连接是更改过的，则需要这样构造

//1.查询全部
var query1 = context.Logs;
DisplayLogs("显示全部的",query1);

//2.查询带筛选
var query2 = context.Logs.Where(l => l.Id % 2 == 1&&l.Message.Contains("Test"));
//2.1 where是c# 3的一个新特性，叫扩展方法
//2.2 l=>1.Id...是C# 3的一个新特性，叫lambda表达式，实际上是一个委托delegate
DisplayLogs("显示奇数的条目", query2);

//3.查询带排序
var query3 = context.Logs.OrderByDescending(l => l.Time);
DisplayLogs("查询带排序", query3);

//4.查询取中间一部分
var query4 = context.Logs.Skip(1).Take(2);
DisplayLogs("查询一部分", query4);

//var query5 = context.Logs.OrderByDescending(l => l.Id).Skip(1).Take(2);
//var query6 = context.Logs.OrderByDescending(l => l.Id).ThenBy(l => l.Time);

//5.插入一个新的条目
var log = new Logs()
{
Message = "测试消息",
Time=DateTime.Now
};
//5.1 {}也是c# 3的新特性，表示直接构造一个对象
context.Logs.InsertOnSubmit(log);
context.SubmitChanges();
DisplayLogs("显示全部的", query1);

//6.更新一个条目
var firstLog = context.Logs.FirstOrDefault(l => l.Id == 1);
if (firstLog != null)
{
firstLog.Message = "修改过之后的消息";
context.SubmitChanges();
DisplayLogs("显示全部的", query1);
}

//7.删除一个条目
var deleteEntry = from l in context.Logs
where l.Id == 1
select l;
var found = deleteEntry.FirstOrDefault();
if (found != null) {
context.Logs.DeleteOnSubmit(found);
context.SubmitChanges();
DisplayLogs("显示全部的", query1);
}

Console.Read();

}

private static void DisplayLogs(string message,
IEnumerable<Logs> query1)
{

Console.WriteLine(message);
foreach (var item in query1)
{
Console.WriteLine("Id:{0},Time:{1},Message:{2}",
item.Id,
item.Time,
item.Message);

}
Console.WriteLine();
}
}
}

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