LINQ(3)

强类型DataContext

public partial class NorthwindDataContext : DataContext {

public Table Customers;

public NorthwindDataContext(IDbConnection connection) : base(connection) { } public NorthwindDataContext(string connection) : base(connection) { } }

强类型数据上下文使代码更简洁：

NorthwindDataContext ctx = new NorthwindDataContext(\ GridView1.DataSource = from c in ctx.Customers where c.CustomerID.StartsWith(\顾客ID = c.CustomerID, 顾客名 = c.Name, 城市 = c.City }; GridView1.DataBind();

DataContext其实封装了很多实用的功能，下面一一介绍。

日志功能

using System.IO;

NorthwindDataContext ctx = new NorthwindDataContext(\ StreamWriter sw = new StreamWriter(Server.MapPath(\ ctx.Log = sw;

GridView1.DataSource = from c in ctx.Customers where c.CustomerID.StartsWith(\顾客ID = c.CustomerID, 顾客名 = c.Name, 城市 = c.City }; GridView1.DataBind(); sw.Close();

运行程序后在网站所在目录生成了log.txt，每次查询都会把诸如下面的日志追加到文本文件中：

SELECT [t0].[CustomerID], [t0].[ContactName], [t0].[City] FROM [Customers] AS [t0]

WHERE [t0].[CustomerID] LIKE @p0

-- @p0: Input String (Size = 2; Prec = 0; Scale = 0) [A%]

-- Context: SqlProvider(Sql2005) Model: AttributedMetaModel Build: 3.5.20706.1 应该说这样的日志对于调试程序是非常有帮助的。

探究查询

using System.Data.Common;

using System.Collections.Generic;

NorthwindDataContext ctx = new NorthwindDataContext(\ var select = from c in ctx.Customers where c.CustomerID.StartsWith(\顾客ID = c.CustomerID, 顾客名 = c.Name, 城市 = c.City }; DbCommand cmd = ctx.GetCommand(select); Response.Write(cmd.CommandText + \ foreach (DbParameter parm in cmd.Parameters)

Response.Write(string.Format(\参数名:{0},参数值:{1}
\ Customer customer = ctx.Customers.First(); customer.Name = \

IList