expressionBuilders Element for compilation (ASP.NET Settings Schema) 

Defines a collection of resource strings to use during compilation. The resource strings associate prefixes with expression builders.

This element is new in the .NET Framework version 2.0.

<expressionBuilders> 
   <add />
   <clear/>
   <remove />
</expressionBuilders>

Attributes and Elements

The following sections describe attributes, child elements, and parent elements.

Attributes

None.

Child Elements

Subtag	Description
add	Optional element. Adds a reference to an expression builder to the collection.
clear	Optional element. Removes all references to inherited expression builders, allowing only the references that are added by the current add element.
remove	Optional element. Removes a reference to an inherited expression builder from the collection.

Parent Elements

Element	Description
configuration	Specifies the root element in every configuration file that is used by the common language runtime and the .NET Framework applications.
system.web	Specifies the root element for the ASP.NET configuration section.
compilation	Configures all compilation settings that ASP.NET uses to compile applications.

Remarks

The expressionBuilders element defines a collection of resource strings to use during compilation. The resource strings associate prefixes with expression builders.

When the page parser encounters an expression in an .aspx page that is delimited with the string <%$ %>, the parser creates an expression builder for the expression based on the prefix in the string. The prefix is the portion of the string that is to the left of the colon (:). For example, when the parser encounters the string <%$ ConnectionStrings:MessageDB %>, the parser creates a ConnectionStringsExpressionBuilder object. For more information, see ExpressionBuilder.

Default Configuration

The following default expressionBuilders element is not explicitly configured in the Machine.config file or in the root Web.config file. However, it is the default configuration that is returned by application. Items are added to the expressionBuilders collection in the root Web.config file.

<expressionBuilders>
   <clear />
</expressionBuilders>

The following default expressionBuilders element is configured in the root Web.config file.

<expressionBuilders>
   <add expressionPrefix="Resources" type="System.Web.Compilation.ResourceExpressionBuilder" />
   <add expressionPrefix="ConnectionStrings" type="System.Web.Compilation.ConnectionStringsExpressionBuilder" />
   <add expressionPrefix="AppSettings" type="System.Web.Compilation.AppSettingsExpressionBuilder" />
</expressionBuilders>

Example

The following code example shows how to register a custom expression builder in the Web.config file. A custom expression builder must implement the ExpressionBuilder abstract class.

To reference the expression in an .aspx file, use the following sytax:

<asp:Label ID="Label1" runat="server"

Text="<%$ MyCustomExpression:Hello, world! %>" />

<configuration>
    <system.web>
       <compilation>
          <expressionBuilders>
              <add expressionPrefix="MyCustomExpression"
               type="MyCustomExpressionBuilder"/>
          </expressionBuilders>
       </compilation>
    </system.web>
</configuration>

Element Information

Configuration section handler	CompilationSection
Configuration member	ExpressionBuilders ExpressionBuilderCollection
Configurable locations	Machine.config Root-level Web.config Application-level Web.config Virtual or physical directory–level Web.config
Requirements	Microsoft Internet Information Services (IIS) version 5.0, 5.1, or 6.0 The .NET Framework version 2.0 Microsoft Visual Studio 2003 or Visual Studio 2005

See Also

Tasks

How to: Configure Specific Directories Using Location Settings
How to: Lock ASP.NET Configuration Settings

Reference

compilation Element (ASP.NET Settings Schema)
add Element for expressionBuilders for compilation (ASP.NET Settings Schema)
clear Element for expressionBuilders for compilation (ASP.NET Settings Schema)
remove Element for expressionBuilders for compilation (ASP.NET Settings Schema)
buildProviders Element for compilation (ASP.NET Settings Schema)
codeSubDirectories Element for compilation (ASP.NET Settings Schema)
compilers Element for compilation (ASP.NET Settings Schema)
assemblies Element for compilation (ASP.NET Settings Schema)
configuration Element (General Settings Schema)
system.web Element (ASP.NET Settings Schema)
System.Configuration
System.Web.Configuration
CompilationSection
ExpressionBuilders
ExpressionBuilderCollection

Concepts

ASP.NET Compilation Model
ASP.NET Web Page Code Model
ASP.NET Web Site Precompilation Overview
ASP.NET Configuration File Hierarchy and Inheritance
Securing ASP.NET Configuration
ASP.NET Configuration Scenarios

Other Resources

General Configuration Settings (ASP.NET)
ASP.NET Configuration Settings
Configuring ASP.NET Applications
ASP.NET Configuration Files
ASP.NET Configuration API