如何取得web.config中connectings中的值

典型的web.config中的connectingSstrings的设置：
<connectionStrings>
    <remove name="LocalSqlServer" />
    <add name="LocalSqlServer" connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|aspnetdb.mdf;User Instance=true" providerName="System.Data.SqlClient"/>
    <add name="MainConnStr" connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|main.mdf;User Instance=true" providerName="System.Data.SqlClient"/>
</connectionStrings>

直接取得值为：

[C#]
string connStr = ConfigurationManager.ConnectionStrings["MainConnStr"].ConnectionString;

[VB]
Dim connStr As String = ConfigurationManager.ConnectionStrings("MainConnStr").ConnectionString

注意，需要使用System.Configuration 命名空间

在SqlDataSource中引用
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:MainConnStr %>"
SelectCommand="SELECT [au_id], [au_lname], [au_fname], [state] FROM [authors]" />