處理 Log 時把資料存放在資料庫是一件很常用的功能，Nlog 並未限制資料庫的結構，這個結構必須要由開發人員自行定義， NLog Database target 可以讓我們輕鬆完成這件事，組態設定的語法如下：
<install-command> <uninstall-command>區段可提供應用程式參數調用，請參考：http://nlog-project.org/2010/09/25/deploying-nlog-configuration.html。
<connectionStringName> 可以拿到 Web.config 的 connectionStrings 的資料。
<commandText> 是用來寫 SQL insert 語法，當然也可以寫 StoredProcedure； Parameter 當然就是新增資料庫的參數，它有兩個必填屬性，name 是資料庫的欄位，layout是 NLog 所提供的 Layout Renderers。
比較特別的是 ${appsetting} ，它是用來拿 appSettings 區段裡的資料，要從 nuget 裡另外安裝 NLog.Extended。
<target xsi:type="Database" name="NLog-SqlServer">
<connectionStringName>elmah-sqlserver</connectionStringName>
<commandText>
insert into dbo.NLog (
Application, Logged, Level, Message,
Username,
ServerName, Port, Url, Https,
ServerAddress, RemoteAddress,
Logger, CallSite, Exception
) values (
@Application, @Logged, @Level, @Message,
@Username,
@ServerName, @Port, @Url, @Https,
@ServerAddress, @RemoteAddress,
@Logger, @Callsite, @Exception
);
</commandText>
<parameter name="@application" layout="${appsetting:Name=ApplicationName:default=Unknown\: set AppName in appSettings}" />
<parameter name="@logged" layout="${date}" />
<parameter name="@level" layout="${level}" />
<parameter name="@message" layout="${message}" />
<parameter name="@username" layout="${identity}" />
<parameter name="@serverName" layout="${aspnet-request:serverVariable=SERVER_NAME}" />
<parameter name="@port" layout="${aspnet-request:serverVariable=SERVER_PORT}" />
<parameter name="@url" layout="${aspnet-request:serverVariable=HTTP_URL}" />
<parameter name="@https" layout="${when:inner=1:when='${aspnet-request:serverVariable=HTTPS}' == 'on'}${when:inner=0:when='${aspnet-request:serverVariable=HTTPS}' != 'on'}" />
<parameter name="@serverAddress" layout="${aspnet-request:serverVariable=LOCAL_ADDR}" />
<parameter name="@remoteAddress" layout="${aspnet-request:serverVariable=REMOTE_ADDR}:${aspnet-request:serverVariable=REMOTE_PORT}" />
<parameter name="@logger" layout="${logger}" />
<parameter name="@callSite" layout="${callsite}" />
<parameter name="@exception" layout="${exception:tostring}" />
</target>
開始前別忘了建立資料表，個人習慣用 SQL Project 將以下 SQL 語法納入管理
CREATE TABLE [dbo].[Log] (
[Id] [int] IDENTITY(1,1) NOT NULL,
[Application] [nvarchar](50) NOT NULL,
[Logged] [datetime] NOT NULL,
[Level] [nvarchar](50) NOT NULL,
[Message] [nvarchar](max) NOT NULL,
[UserName] [nvarchar](250) NULL,
[ServerName] [nvarchar](max) NULL,
[Port] [nvarchar](max) NULL,
[Url] [nvarchar](max) NULL,
[Https] [bit] NULL,
[ServerAddress] [nvarchar](100) NULL,
[RemoteAddress] [nvarchar](100) NULL,
[Logger] [nvarchar](250) NULL,
[Callsite] [nvarchar](max) NULL,
[Exception] [nvarchar](max) NULL,
CONSTRAINT [PK_dbo.Log] PRIMARY KEY CLUSTERED ([Id] ASC)
WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
文章出自：https://www.dotblogs.com.tw/yc421206/2015/11/23/nlog_database_target
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Microsoft MVP Award 2010~2017 C# 第四季
Microsoft MVP Award 2018~2022 .NET
