强类型DataContext
public partial class NorthwindDataContext : DataContext
{
public Table<Customer> Customers;
public NorthwindDataContext(IDbConnection connection) : base(connection) { }
public NorthwindDataContext(string connection) : base(connection) { }
}
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强类型数据上下文使代码更简洁:
NorthwindDataContext ctx = new NorthwindDataContext("server=xxx;database=Northwind;uid=xxx;pwd=xxx");
GridView1.DataSource = from c in ctx.Customers where c.CustomerID.StartsWith("A") select new { 顾客ID = c.CustomerID, 顾客名 = c.Name, 城市 = c.City };
GridView1.DataBind();
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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("server=xxx;database=Northwind;uid=xxx;pwd=xxx");
StreamWriter sw = new StreamWriter(Server.MapPath("log.txt"), true); // Append
ctx.Log = sw;
GridView1.DataSource = from c in ctx.Customers where c.CustomerID.StartsWith("A") select new { 顾客ID = c.CustomerID, 顾客名 = c.Name, 城市 = c.City };
GridView1.DataBind();
sw.Close();
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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
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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("server=xxx;database=Northwind;uid=xxx;pwd=xxx");
var select = from c in ctx.Customers where c.CustomerID.StartsWith("A") select new { 顾客ID = c.CustomerID, 顾客名 = c.Name, 城市 = c.City };
DbCommand cmd = ctx.GetCommand(select);
Response.Write(cmd.CommandText + "<br/>");
foreach (DbParameter parm in cmd.Parameters)
Response.Write(string.Format("参数名:{0},参数值:{1}<br/>", parm.ParameterName, parm.Value));
Customer customer = ctx.Customers.First();
customer.Name = "zhuye";
IList<object> queryText = ctx.GetChangeSet().ModifiedEntities;
Response.Write(((Customer)queryText[0]).Name);
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在这里,我们通过DataContext的GetCommand方法获取了查询对应的DbCommand,
并且输出了CommandText和所有的DbParameter。之后,我们又通过GetChangeSet方法获取了修改后的实体,
并输出了修改内容。