LINQ入门之访问数据库（插，删，改）［转］

输入您的搜索字词 提交搜索表单

以博客园的系统为例子，既然称linq to sql为一个orm框架，orm，对象-关系 映射，既然o在前关系在后，说明o为重，关系是根据o得来的，那么我们就先新建一些entity object吧。在一个博客系统里最常见的就是user,blog,post。

一个用户有且仅有一个博客，而一个博客可以有零篇或者多篇博客文章。根据这个描述我们来建立entity：



step 1 建立实体对象


public class user
<img id="codehighlighter1_55_715_open_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_55_715_open_text').style.display='none'; document.getelementbyid('codehighlighter1_55_715_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_55_715_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedblockstart.gif" align="top" alt="" /><img id="codehighlighter1_55_715_closed_image" style="display: inline" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_55_715_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_55_715_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_55_715_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedblock.gif" align="top" alt="" />/// <summary>
        /// 用户标识
        /// </summary>
<img id="codehighlighter1_141_154_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_141_154_open_text').style.display='none'; document.getelementbyid('codehighlighter1_141_154_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_141_154_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_141_154_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_141_154_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_141_154_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_141_154_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public int id { get; set; }
<img id="codehighlighter1_163_247_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_163_247_open_text').style.display='none'; document.getelementbyid('codehighlighter1_163_247_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_163_247_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_163_247_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_163_247_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_163_247_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_163_247_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 该用户对应的博客，
        /// 一个用户有且仅有一个博客
        /// </summary>
<img id="codehighlighter1_272_285_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_272_285_open_text').style.display='none'; document.getelementbyid('codehighlighter1_272_285_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_272_285_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_272_285_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_272_285_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_272_285_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_272_285_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public blog blog { get; set; }
<img id="codehighlighter1_294_347_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_294_347_open_text').style.display='none'; document.getelementbyid('codehighlighter1_294_347_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_294_347_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_294_347_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_294_347_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_294_347_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_294_347_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 用户名
        /// </summary>
<img id="codehighlighter1_378_391_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_378_391_open_text').style.display='none'; document.getelementbyid('codehighlighter1_378_391_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_378_391_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_378_391_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_378_391_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_378_391_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_378_391_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public string username { get; set; }
<img id="codehighlighter1_400_452_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_400_452_open_text').style.display='none'; document.getelementbyid('codehighlighter1_400_452_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_400_452_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_400_452_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_400_452_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_400_452_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_400_452_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 密码
        /// </summary>
<img id="codehighlighter1_483_496_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_483_496_open_text').style.display='none'; document.getelementbyid('codehighlighter1_483_496_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_483_496_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_483_496_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_483_496_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_483_496_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_483_496_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public string password { get; set; }
<img id="codehighlighter1_505_557_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_505_557_open_text').style.display='none'; document.getelementbyid('codehighlighter1_505_557_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_505_557_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_505_557_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_505_557_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_505_557_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_505_557_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 昵称
        /// </summary>
<img id="codehighlighter1_588_601_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_588_601_open_text').style.display='none'; document.getelementbyid('codehighlighter1_588_601_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_588_601_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_588_601_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_588_601_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_588_601_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_588_601_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public string nickname { get; set; }
<img id="codehighlighter1_610_666_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_610_666_open_text').style.display='none'; document.getelementbyid('codehighlighter1_610_666_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_610_666_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_610_666_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_610_666_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_610_666_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_610_666_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 用户离开时间
        /// </summary>
<img id="codehighlighter1_700_713_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_700_713_open_text').style.display='none'; document.getelementbyid('codehighlighter1_700_713_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_700_713_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_700_713_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_700_713_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_700_713_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_700_713_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public datetime leavetime { get; set; }
}  

<img id="code_closed_image_084041" style="display: inline" onclick="this.style.display='none'; document.getelementbyid('code_closed_text_084041').style.display='none'; document.getelementbyid('code_open_image_084041').style.display='inline'; document.getelementbyid('code_open_text_084041').style.display='inline';" height="16" src="http://www.cnblogs.com/images/outliningindicators/contractedblock.gif" width="11" align="top" alt="" /><img id="code_open_image_084041" style="display: none" onclick="this.style.display='none'; document.getelementbyid('code_open_text_084041').style.display='none'; getelementbyid('code_closed_image_084041').style.display='inline'; getelementbyid('code_closed_text_084041').style.display='inline';" height="16" src="http://www.cnblogs.com/images/outliningindicators/expandedblockstart.gif" width="11" align="top" alt="" />user <summary>
/// 用户类
/// </summary>

<img id="code_closed_image_084114" style="display: inline" onclick="this.style.display='none'; document.getelementbyid('code_closed_text_084114').style.display='none'; document.getelementbyid('code_open_image_084114').style.display='inline'; document.getelementbyid('code_open_text_084114').style.display='inline';" height="16" src="http://www.cnblogs.com/images/outliningindicators/contractedblock.gif" width="11" align="top" alt="" /><img id="code_open_image_084114" style="display: none" onclick="this.style.display='none'; document.getelementbyid('code_open_text_084114').style.display='none'; getelementbyid('code_closed_image_084114').style.display='inline'; getelementbyid('code_closed_text_084114').style.display='inline';" height="16" src="http://www.cnblogs.com/images/outliningindicators/expandedblockstart.gif" width="11" align="top" alt="" />blog/// <summary>
    /// 博客类
    /// </summary>
    public class blog
<img id="codehighlighter1_71_614_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_71_614_open_text').style.display='none'; document.getelementbyid('codehighlighter1_71_614_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_71_614_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedblockstart.gif" align="top" alt="" /><img id="codehighlighter1_71_614_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_71_614_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_71_614_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_71_614_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedblock.gif" align="top" alt="" />    {
<img id="codehighlighter1_81_135_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_81_135_open_text').style.display='none'; document.getelementbyid('codehighlighter1_81_135_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_81_135_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_81_135_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_81_135_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_81_135_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_81_135_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 博客标识
        /// </summary>
<img id="codehighlighter1_157_170_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_157_170_open_text').style.display='none'; document.getelementbyid('codehighlighter1_157_170_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_157_170_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_157_170_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_157_170_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_157_170_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_157_170_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public int id { get; set; }
<img id="codehighlighter1_179_240_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_179_240_open_text').style.display='none'; document.getelementbyid('codehighlighter1_179_240_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_179_240_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_179_240_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_179_240_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_179_240_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_179_240_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 用户标识，和用户相关联
        /// </summary>
<img id="codehighlighter1_266_279_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_266_279_open_text').style.display='none'; document.getelementbyid('codehighlighter1_266_279_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_266_279_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_266_279_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_266_279_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_266_279_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_266_279_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public int userid { get; set; }
<img id="codehighlighter1_288_344_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_288_344_open_text').style.display='none'; document.getelementbyid('codehighlighter1_288_344_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_288_344_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_288_344_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_288_344_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_288_344_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_288_344_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 博客的中文名
        /// </summary>
<img id="codehighlighter1_371_384_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_371_384_open_text').style.display='none'; document.getelementbyid('codehighlighter1_371_384_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_371_384_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_371_384_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_371_384_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_371_384_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_371_384_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public string name { get; set; }
<img id="codehighlighter1_393_447_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_393_447_open_text').style.display='none'; document.getelementbyid('codehighlighter1_393_447_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_393_447_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_393_447_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_393_447_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_393_447_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_393_447_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 创建时间
        /// </summary>
<img id="codehighlighter1_482_495_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_482_495_open_text').style.display='none'; document.getelementbyid('codehighlighter1_482_495_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_482_495_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_482_495_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_482_495_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_482_495_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_482_495_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public datetime createdate { get; set; }
<img id="codehighlighter1_504_566_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_504_566_open_text').style.display='none'; document.getelementbyid('codehighlighter1_504_566_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_504_566_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_504_566_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_504_566_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_504_566_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_504_566_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 一个博客有零篇或多篇文章
        /// </summary>
<img id="codehighlighter1_599_612_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_599_612_open_text').style.display='none'; document.getelementbyid('codehighlighter1_599_612_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_599_612_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_599_612_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_599_612_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_599_612_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_599_612_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public ilist
posts { get; set; }
}
<img id="code_closed_image_084144" style="display: inline" onclick="this.style.display='none'; document.getelementbyid('code_closed_text_084144').style.display='none'; document.getelementbyid('code_open_image_084144').style.display='inline'; document.getelementbyid('code_open_text_084144').style.display='inline';" height="16" src="http://www.cnblogs.com/images/outliningindicators/contractedblock.gif" width="11" align="top" alt="" /><img id="code_open_image_084144" style="display: none" onclick="this.style.display='none'; document.getelementbyid('code_open_text_084144').style.display='none'; getelementbyid('code_closed_image_084144').style.display='inline'; getelementbyid('code_closed_text_084144').style.display='inline';" height="16" src="http://www.cnblogs.com/images/outliningindicators/expandedblockstart.gif" width="11" align="top" alt="" />code/// <summary>
/// 博客文章类
/// </summary>
public class post
<img id="codehighlighter1_57_577_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_57_577_open_text').style.display='none'; document.getelementbyid('codehighlighter1_57_577_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_57_577_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedblockstart.gif" align="top" alt="" /><img id="codehighlighter1_57_577_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_57_577_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_57_577_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_57_577_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedblock.gif" align="top" alt="" />{
<img id="codehighlighter1_67_121_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_67_121_open_text').style.display='none'; document.getelementbyid('codehighlighter1_67_121_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_67_121_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_67_121_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_67_121_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_67_121_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_67_121_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 文章id
        /// </summary>
<img id="codehighlighter1_143_156_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_143_156_open_text').style.display='none'; document.getelementbyid('codehighlighter1_143_156_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_143_156_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_143_156_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_143_156_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_143_156_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_143_156_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public int id { get; set; }
<img id="codehighlighter1_165_222_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_165_222_open_text').style.display='none'; document.getelementbyid('codehighlighter1_165_222_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_165_222_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_165_222_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_165_222_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_165_222_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_165_222_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 文章从属的博客
        /// </summary>
<img id="codehighlighter1_248_261_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_248_261_open_text').style.display='none'; document.getelementbyid('codehighlighter1_248_261_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_248_261_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_248_261_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_248_261_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_248_261_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_248_261_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public int blogid { get; set; }
<img id="codehighlighter1_270_322_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_270_322_open_text').style.display='none'; document.getelementbyid('codehighlighter1_270_322_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_270_322_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_270_322_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_270_322_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_270_322_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_270_322_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 标题
        /// </summary>
<img id="codehighlighter1_350_363_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_350_363_open_text').style.display='none'; document.getelementbyid('codehighlighter1_350_363_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_350_363_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_350_363_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_350_363_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_350_363_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_350_363_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public string title { get; set; }
<img id="codehighlighter1_372_424_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_372_424_open_text').style.display='none'; document.getelementbyid('codehighlighter1_372_424_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_372_424_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_372_424_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_372_424_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_372_424_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_372_424_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 内容
        /// </summary>
<img id="codehighlighter1_451_464_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_451_464_open_text').style.display='none'; document.getelementbyid('codehighlighter1_451_464_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_451_464_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_451_464_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_451_464_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_451_464_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_451_464_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public string body { get; set; }
<img id="codehighlighter1_473_527_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_473_527_open_text').style.display='none'; document.getelementbyid('codehighlighter1_473_527_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_473_527_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_473_527_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_473_527_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_473_527_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_473_527_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        /// <summary>
        /// 发表时间
        /// </summary>
<img id="codehighlighter1_562_575_open_image" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_562_575_open_text').style.display='none'; document.getelementbyid('codehighlighter1_562_575_closed_image').style.display='inline'; document.getelementbyid('codehighlighter1_562_575_closed_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/expandedsubblockstart.gif" align="top" alt="" /><img id="codehighlighter1_562_575_closed_image" style="display: none" onclick="this.style.display='none'; document.getelementbyid('codehighlighter1_562_575_closed_text').style.display='none'; document.getelementbyid('codehighlighter1_562_575_open_image').style.display='inline'; document.getelementbyid('codehighlighter1_562_575_open_text').style.display='inline';" src="http://www.cnblogs.com/images/outliningindicators/contractedsubblock.gif" align="top" alt="" />        public datetime createdate { get; set; }
}
我们先不要谈论这个设计是否合理，也不要谈论这三个实体是贫血模型还是充血模型。

对象建立好了，我们来建设数据库表吧：users表，blogs表，posts表(为什么表都用复数?从rails里学过来的，activerecord模式里，表里每条记录都对应着一个对象，所以表用复数表示，这是一种约定)



step 2：创建数据库表

users表：

<img height="118" alt="" src="http://images.cnblogs.com/cnblogs_com/yuyijq/howdoi/howdoi_1.jpg" width="391" border="0" />
blogs表：
<img height="119" alt="" src="http://images.cnblogs.com/cnblogs_com/yuyijq/howdoi/howdoi_2.jpg" width="366" border="0" />
posts表：
<img height="139" alt="" src="http://images.cnblogs.com/cnblogs_com/yuyijq/howdoi/howdoi_3.jpg" width="367" border="0" />
我们注意到，用户类里的leavetime离开时间在数据库里并没有对应的字段，因为这个是用来临时记路用户离开离开博客园的时间的，这样可以用来做一些在线统计，所以无需持久化。



step 3:建立映射

对象也有了，关系也有了，那剩下的是什么？对，就是映射，我们怎样将对象映射到数据库表上？

我们从最简单的post开始吧：
<!--



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-->/// <summary>
    /// 博客文章类
    /// 这个类和数据库里的posts表对应，由于
    /// 类名和表名不一样，所以需要显式的指明table特性的name属性
    /// 如果是一致的则无需指明了
    /// </summary>
    [table(name="posts")]
    public class post
    {
        /// <summary>
        /// 文章id
        /// 这个对应posts表里的postid
        /// 这个字段还是一个主键,所以column特性的isprimarykey属性为true
        /// </summary>
        [column(name="postid",isprimarykey=true)]
        public int id { get; set; }
        /// <summary>
        /// 文章从属的博客
        /// 这个对应着表里的blogid，名字一样所以只需要加个column特性就可以了
        /// 下面几个也是一样的意思
        /// </summary>
        [column]
        public int blogid { get; set; }
        /// <summary>
        /// 标题
        /// </summary>
        [column]
        public string title { get; set; }
        /// <summary>
        /// 内容
        /// </summary>
        [column]
        public string body { get; set; }
        /// <summary>
        /// 发表时间
        /// </summary>
        [column]
        public datetime createdate { get; set; }
}
仔细看看注释里面的说明，很简单吧，在类上面加table特性，属性上加column特性。

映射建完了，我们可以施加一些操作了。

在上一篇文章里介绍了，linq to sql的入口点是datacontext类，这个类主要做这么几件事情：

将我们用c#写的这个查询翻译成sql语句，当然也并不是他全权负责翻译工作。

执行查询

连接的管理，这样我们就不用写啥connection了啊，也不用担心数据库的连接和关闭的问题。



step 4：执行查询

那我们就首先实例化一个datacontext类吧(为了好测试，使用一个控制台程序)：从这里可以看出，datacontext需要一个连接字符串，在datacontext里，我们打交道最多的就是gettable<tentity>()方法，这里的tentity就是我们上面的那个post了，带有映射的实体，这个方法返回一个table<tentity>对象：
<!--



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-->table<tentity> posts = dbcontext.gettable
();
实际上，table<tentity>实现了ienumerable<tentity>接口，那这里实际上是返回了一个ienumerable
系列，那我们可以对posts进行遍历了：
<!--



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-->foreach(var post in posts)
       console.writeline(post.title);

实际上，如果光返回一个table<tentity>，而不在上面施加任何的操作，遍历的时候是返回整个表的数据，在上一篇我还提到，为了跟踪，我们最好将dbcontext.log给显示出来。如果你添加了下面这行代码：
<!--



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-->dbcontext.log = console.out;
(对于这行代码，如果你使用的是控制台程序，那么输出就会显示在命令窗口里，如果你用的是winform程序调试，那么输出会显示在vs的output窗口里)

那你将会从控制台里得到下面的东东：
<img height="121" alt="" src="http://images.cnblogs.com/cnblogs_com/yuyijq/howdoi/howdoi_4.jpg" width="648" border="0" />
这就是linq为你生成的sql语句，是不在是比你写的还标准啊，呵呵。

当然，我们常常做的肯定不是像上面这样的全查询，我们还要附加一些条件的。

上一篇还提到过：由于table<tentity>实现了ienumerable<tentity>接口，那么所有的查询表达式都可以在这里使用了，这样你先前在linq to objects里学到东西现在又有了新的用途了：

比如我们可以对blogid做筛选：
<!--



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-->var posts = from post in dbcontext.gettable
()
         where post.blogid == 2
         select post;
(ps：我在写linq语法的时候，因为linq的风格太像sql语句了，所以一些地方比如 ==我老写成=，而&&经常写成”and”，希望大家不要烦我这样的低级错误，呵呵)

看看这次生成的sql语句：

可以看到生成的sql语句对blogid做了筛选，而且值得庆祝的是，linq to sql为我们生成的sql语句还使用的是参数，她并不是仅仅将数值和语句组合在一起。关于使用参数而不是拼凑起来的sql语句的好处在这里啰嗦两句，主要有两点：<img height="125" alt="" src="http://images.cnblogs.com/cnblogs_com/yuyijq/howdoi/howdoi_6.jpg" width="657" border="0" />
面对这样的一个linq查询，linq to sql居然知道将它翻译成like子句，从上图倒数第二行最后中括号里面的东西可以看出，linq to sql还知道将传入的参数设置为y%，我不得不惊叹：太强大了。

但是不是所有的c#的方法都可以使用呢？答案是否定的。比如：我想对最后查出来的文章的创建时间做个格式化，居然报错了，说不支持这种“翻译”。那看来每次我们做查询的时候是要先try一下。

上面只是做了筛选的实例，你还可以去尝试一下排序和分组，这个和linq to objects里的用法是一样的，你可以到前面的文章里复习一下。



step 5：插入对象

本系列的文章到现在为止都是在介绍查询，难道linq to sql只能做查询么？不能向数据库添加数据？，肯定不是的：生成的sql语句：
<img height="147" alt="" src="http://images.cnblogs.com/cnblogs_com/yuyijq/howdoi/howdoi_7.jpg" width="637" border="0" />
一个简单的不能再简单的insert into语句，加上一条返回新插入记录的标识值的语句。

如果你按照本文所说的一步步往下来，在执行上面的插入的时候肯定会碰到异常，这是因为，id对应的数据表字段postid是该表的主键，你不应该在插入的时候赋值，有人说我实例化对象的时候确实没有给post的id属性赋值啊，但是.net会在后台为我们将id赋值为0，所以你要对映射对象做一下修改：
<!--



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-->[column(name="postid",isprimarykey=true,isdbgenerated=true)]
public int id { get; set; }

不仅仅数据表的主键要加这个属性，如果对于那些在数据库里设置了默认值的，你并不像用程序插入的时候，你也得使用，比如这里的createdate。



step 6：更新数据

可以插入肯定就可以更新了，下面就来看看如何更新呢：

做更新的时候，你首先得从数据库查询出该对象，然后对该对象的属性进行修改，最后更新到数据库：linq to sql也会自动的帮你生成update语句了。

有了插入，更新，查询就差一个delete curd就全了，对于delete更简单了，你只要调用table<tentity>的deleteonsubmit方法就行了，这里就不再详述。



注意：需添加
using system.data.linq.mapping;命名空间。


上面表post中body字段类型应该为vchar（50），在调试进行update表时发生异常，说类型不匹配。原因在找中....  



<!--



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-->var posts = from post in dbcontext.gettable
()
        where post.blogid == 2
        select post;
foreach (var post in posts)
     post.blogid = 5;

dbcontext.submitchanges();


<!--



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-->table
posts = dbcontext.gettable
();
//先实例化一个新的要插入的对象
post post = new post();
post.blogid = 2;
post.title = "test";
post.body = "test,test,test,test";
post.createdate = datetime.now;
//调用table<tentity>的insertonsubmit方法
posts.insertonsubmit(post);
//把改变提交到数据库，这个时候才真正执行了
dbcontext.submitchanges();
//提交修改后，你就可以查询新插入的post的id了
console.writeline(post.id);

<!--



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-->var posts = from post in dbcontext.gettable
()
         where post.title.startswith("y")
         select post.createdate.tostring("yyyy-mm-dd");


这样可以有效的sql注入攻击，这个hack手段曾经让很多网站吃尽了苦头。

使用参数可以利用sql server对sql语句的缓存和预编译作用，因为使用参数的sql语句可能多次用到，而拼凑起来的sql语句却和特定的查询有关。

这样的筛选还不能体现出linq的智能了，请再看这个：
<!--



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-->var posts = from post in dbcontext.gettable
()
         where post.title.startswith("y")
         select post;

<!--



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-->datacontext dbcontext = new datacontext(configurationmanager.connectionstrings["cnblogs"].connectionstring);