Code
<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
        <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net"/>
    </configSections>
  <log4net>
    <appender name="ADONetAppender" type="log4net.Appender.AdoNetAppender">
      <bufferSize value="1" />
      <connectionType value="System.Data.SqlClient.SqlConnection, System.Data, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" />
      <connectionString value="server=codebase;database=StuDepartmentOA;uid=sadis;pwd=123;timeout=300;" />
      <commandText value="INSERT INTO ErrLog ([Time],[errLevel],[Info],[Exception]) VALUES (@time, @level, @info, @exception)" />
      <parameter>
        <parameterName value="@time" />
        <dbType value="DateTime" />
        <layout type="log4net.Layout.RawTimeStampLayout" />
      </parameter>
      <parameter>
        <parameterName value="@level" />
        <dbType value="String" />
        <size value="8" />
        <layout type="log4net.Layout.PatternLayout">
          <conversionPattern value="%p" />
        </layout>
      </parameter>
      <parameter>
        <parameterName value="@info" />
        <dbType value="String" />
        <size value="200" />
        <layout type="log4net.Layout.PatternLayout">
          <conversionPattern value="%m" />
        </layout>
      </parameter>
      <parameter>
        <parameterName value="@exception" />
        <dbType value="String" />
        <size value="1000" />
        <layout type="log4net.Layout.PatternLayout">
          <conversionPattern value="%exception" />
        </layout>
      </parameter>
    </appender>
    <appender name="FileErrLogAppender" type="log4net.Appender.RollingFileAppender">
      <!--日志文件的存储路径-->
      <file value="bin\Log\"/>
      <appendToFile value="true"/>
      <rollingStyle value="Date"/>
      <datePattern value="yyyy-MM-dd.LOG"/>
      <!--根据日期，定义文件名-->
      <staticLogFileName value="false"/>
      <!--日志文件输出格式-->
      <layout  type="log4net.Layout.PatternLayout">
        <param name="Header" value="[Header]"/>
        <param name="Footer" value="[Footer]"/>
        <ConversionPattern value="%nTime: %d %n Level: %level   Info: %message %nException: %exception"/>
      </layout>
    </appender>

<!-- Setup the root category, add the appenders and set the default level -->
    <root>
      <level value="WARN"/>
      <level value="INFO"/>
      <level value="DEBUG"/>
    </root>
    <!-- Specify the level for some specific categories -->
    <logger name="logger">
      <level value="WARN"/>
      <level value="INFO"/>
      <level value="DEBUG"/>
      <appender-ref ref="FileErrLogAppender"/>  
      <appender-ref ref="ADONetAppender" />
    </logger>

</log4net>
</configuration>

Code
USE [StuDepartmentOA]
GO
/****** 对象:  Table [dbo].[ErrLog]    脚本日期: 08/16/2009 10:09:31 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[ErrLog](
    [ID] [int] IDENTITY(1,1) NOT NULL,
    [time] [datetime] NOT NULL,
    [errLevel] [varchar](8) COLLATE Chinese_PRC_CI_AS NOT NULL,
    [info] [nvarchar](200) COLLATE Chinese_PRC_CI_AS NOT NULL,
    [exception] [varchar](1000) COLLATE Chinese_PRC_CI_AS NULL,
 CONSTRAINT [PK_errLog] PRIMARY KEY CLUSTERED 
(
    [ID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]

GO
SET ANSI_PADDING OFF

log4net.Config.XmlConfigurator.ConfigureAndWatch(new System.IO.FileInfo(Server.MapPath("~") + @"\log4net.config"));

Code
using System;
using log4net;
namespace DAL
{
    /// <summary>
    /// LogHelper 的摘要说明
    /// </summary>
    public class LogHelper
    {
        private static ILog Logger = log4net.LogManager.GetLogger("logger");
        public static void Debug(string message, Exception ex)
        {
            if(Logger.IsDebugEnabled)
            {
                Logger.Debug(message, ex);
            }
        }
        public static void Debug(string message)
        {
            if (Logger.IsDebugEnabled)
            {
                Logger.Debug(message);
            }
        }
        public static void Info(string message, Exception ex)
        {
            if(Logger.IsInfoEnabled)
            {
                Logger.Info(message, ex);
            }
        }
        public static void Info(string message)
        {
            if (Logger.IsInfoEnabled)
            {
                Logger.Info(message);
            }
        }
        public static void Error(string message, Exception ex)
        {
            if (Logger.IsErrorEnabled)
            {
                Logger.Error(message,ex);
            }
        }
        public static void Error(string message)
        {
            if (Logger.IsErrorEnabled)
            {
                Logger.Error(message);
            }
        }
    }
}