主攻ASP.NET.3.5.MVC架构之重生: LINQ(五)

LINQ to SQL

下载LINQ to SQL Debug Visualizer

http://www.scottgu.com/blogposts/linqquery/sqlserverQueryVisualizer.zip

LINQ to SQL执行标准数据库命令

*查询文章类别ID为34的文章标题并排序取4条 Take()取元素条数 =>Top

LINQ to SQL Code

            MydataDataContext data = new MydataDataContext();

            var query = data.Article.Where(m => m.CategoryID == 34)

                                    .OrderBy(m => m.Sort)

                                    .Select(m => new { m.ArticleID, m.ArticleTitle ,m.ArticleBody})

                                    .Take(4);

SqlCode

SELECT TOP (4) [t0].[ArticleID], [t0].[ArticleTitle], [t0].[ArticleBody]

FROM [dbo].[Article] AS [t0]

WHERE [t0].[CategoryID] = 34

ORDER BY [t0].[Sort]

*查询文章类别ID为34的文章标题并排序

LINQ to SQL Code

            MydataDataContext data = new MydataDataContext();

            var query = data.Article.Where(m => m.CategoryID == 34)

                                    .OrderBy(m => m.Sort)

                                    .Select(m => m.ArticleTitle);

SqlCode

SELECT [t0].[ArticleTitle]

FROM [dbo].[Article] AS [t0]

WHERE [t0].[CategoryID] = 34

ORDER BY [t0].[Sort]

*查询文章类别ID为34的文章标题，文章ID，文章内容并排序

LINQ to SQL Code

            MydataDataContext data = new MydataDataContext();

            var query = data.Article.Where(m => m.CategoryID == 34)

                                    .OrderBy(m => m.Sort)

                                    .Select(m => new { m.ArticleID, m.ArticleTitle ,m.ArticleBody});  

SqlCode

SELECT [t0].[ArticleID], [t0].[ArticleTitle], [t0].[ArticleBody]

FROM [dbo].[Article] AS [t0]

WHERE [t0].[CategoryID] = 34

ORDER BY [t0].[Sort]

*查询文章所有项

LINQ to SQL Code

            MydataDataContext data = new MydataDataContext();

            var query = from m in data.Article select m;

SqlCode

SELECT [t0].[ArticleID], [t0].[CategoryID], [t0].[ArticleTitle], [t0].[ArticleBody], [t0].[IsTop], [t0].[Sort], [t0].[CreateTime], [t0].[SysUserID], [t0].[State]

FROM [dbo].[Article] AS [t0]

*查询文章选择项

LINQ to SQL Code

            MydataDataContext data = new MydataDataContext();

            var query = data.Article.Select(m => new { m.ArticleID, m.ArticleTitle });

SqlCode

SELECT [t0].[ArticleID], [t0].[ArticleTitle]

FROM [dbo].[Article] AS [t0]

IEnumerable和IEnumerable<T>接口

IQueryProvider和IQueryable<T>接口

IQueryable

Lambda表达式

Code:

MyDataDataContext data = new MyDataDataContext();                                         //使用LINQ类

var s = from n in data.Article where n.ArticleID == 21 select n;                //执行查询

foreach (var t in s)                                                                                                            //遍历对象

{

         Response.Write(t.ArticleTitle.ToString() + "<br/>");                             //输出对象

}