Web.config Transformation Syntax for Web Application Project Deployment
Updated: May 2011
Web.config files typically include settings that have to be different depending on which environment the application is running in. For example, you might have to change a database connection string or disable debugging when you deploy a Web.config file. For Web application projects, ASP.NET provides tools that automate the process of changing (transforming) Web.config files when they are deployed. For each environment that you want to deploy to, you create a transform file that specifies only the differences between the original Web.config file and the deployed Web.config file for that environment.
A transform file is an XML file that specifies how the Web.config file should be changed when it is deployed. Transformation actions are specified by using XML attributes that are defined in the XML-Document-Transform namespace, which is mapped to the xdt prefix. The XML-Document-Transform namespace defines two attributes: Locator and Transform. The Locator attribute specifies the Web.config element or set of elements that you want to change in some way. The Transformattribute specifies what you want to do to the elements that the Locator attribute finds.
The following example shows the contents of a transform file that changes a connection string and replaces the customErrors element:
<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
<connectionStrings>
<add name="MyDB"
connectionString="value for the deployed Web.config file"
xdt:Transform="SetAttributes" xdt:Locator="Match(name)"/>
</connectionStrings>
<system.web>
<customErrors defaultRedirect="GenericError.htm"
mode="RemoteOnly" xdt:Transform="Replace">
<error statusCode="500" redirect="InternalError.htm"/>
</customErrors>
</system.web>
</configuration>
The root element of a transform file must specify the XML-Document-Transform namespace in its opening tag, as shown in the preceding example. The Locator and Transform elements themselves are not reproduced in the deployed Web.config file.
This following sections provide reference information about the syntax to use in transform files.
Locator Attribute Syntax
Each of the following sections explains the syntax for one Locator attribute.
Condition
Specifies an XPath expression that is appended to the current element's XPath expression. Elements that match the combined XPath expression are selected.
Syntax
Locator="Condition(XPath expression)"
Example
The following example shows how to select connection string elements whose name attribute value is oldname or a providerName attribute whose value is oldprovider. In the deployed Web.config file, the selected elements are replaced with the element that is specified in the transform file.
<configuration xmlns:xdt="...">
<connectionStrings>
<add name="AWLT" connectionString="newstring"
providerName="newprovider"
xdt:Transform="Replace"
xdt:Locator="Condition(@name='oldname'
or @providerName='oldprovider')" />
</connectionStrings>
</configuration>
The effective XPath expression that is applied to the development Web.config file as a result of the specified Condition expression is the following:
configuration/connectionStrings/add[@name='AWLT' or @providerName='System.Data.SqlClient']
This expression is a result of combining the implicit XPath condition for the current element (configuration/connectionStrings) with the expression that is specified explicitly.
Match
Selects the element or elements that have a matching value for the specified attribute or attributes. If multiple attribute names are specified, only elements that match all the specified attributes are selected.
Syntax
Locator="Match(comma-delimited list of one or more attribute names)"
Example
The following example shows how to select the connection string add element that has AWLT in the name attribute in the development Web.config file. In the deployed Web.config file, the selected element is replaced with the add element that is specified in the transform file.
<configuration xmlns:xdt="...">
<connectionStrings>
<add name="AWLT" connectionString="newstring"
providerName="newprovider"
xdt:Transform="Replace"
xdt:Locator="Match(name)" />
</connectionStrings>
</configuration>
XPath
Specifies an absolute XPath expression that is applied to the development Web.config file. (Unlike Condition, the expression that you specify is not appended to the implicit XPath expression that corresponds to the current element.)
Syntax
Locator="XPath(XPath expression)"
Example
The following example shows how to select the same elements that are selected by the preceding example for the Condition keyword.
<configuration xmlns:xdt="...">
<connectionStrings>
<add name="AWLT" connectionString="newstring"
providerName="newprovider"
xdt:Transform="Replace"
xdt:Locator="XPath(configuration/connectionStrings[@name='AWLT'
or @providerName='System.Data.SqlClient'])" />
</connectionStrings>
</configuration>
Transform Attribute Syntax
Each of the following sections explains the syntax for one Transform attribute.
Replace
Replaces the selected element with the element that is specified in the transform file. If more than one element is selected, only the first selected element is replaced. For an example of how to use the Replace keyword, see the examples for the Locator attributes.
Syntax
Transform="Replace"
Insert
Adds the element that is defined in the transform file as a sibling to the selected element or elements. The new element is added at the end of any collection.
Syntax
Transform="Insert"
Example
The following example shows how to select all the connection strings in the development Web.config file. In the deployed Web.config file, the specified connection string is added to the end of the collection.
<configuration xmlns:xdt="...">
<connectionStrings>
<add name="AWLT" connectionString="newstring"
providerName="newprovider"
xdt:Transform="Insert" />
</connectionStrings>
</configuration>
InsertBefore
Inserts the element that is defined in the transform XML directly before the element that is selected by the specified XPath expression. The XPath expression must be an absolute expression, because it is applied to the development Web.config file as a whole; it is not appended only to the current element's implicit XPath expression.
Syntax
Transform="InsertBefore(XPath expression)"
Example
The following example shows how to select the deny element that denies access to all users, and then inserts an allow element before it that grants access to administrators.
<configuration xmlns:xdt="...">
<authorization>
<allow roles="Admins"
xdt:Transform="InsertBefore(/configuration/system.web/authorization/deny[@users='*'])" />
</authorization>
</configuration>
InsertAfter
Inserts the element that is defined in the transform XML directly after the element that is selected by the specified XPath expression. The XPath expression must be an absolute expression, because it is applied to the development Web.config file as a whole; it is not appended to the current element's implicit XPath expression.
Syntax
Transform="InsertAfter(XPath expression)"
Example
The following example shows how to select the allow element that grants access to administrators, and inserts a deny element after it that denies access to a specified user.
<configuration xmlns:xdt="...">
<authorization>
<deny users="UserName"
xdt:Transform="InsertAfter
(/configuration/system.web/authorization/allow[@roles='Admins'])" />
</authorization>
</configuration>
Remove
Removes the selected element. If multiple elements are selected, removes the first element.
Syntax
Transform="Remove"
Example
The following example shows how to select all the connection string add elements in the development Web.config file. In the deployed Web.config file, only the first connection string element is removed.
<configuration xmlns:xdt="...">
<connectionStrings>
<add xdt:Transform="Remove" />
</connectionStrings>
</configuration>
RemoveAll
Removes the selected element or elements.
Syntax
Transform="RemoveAll"
Example
The following example shows how to select all the connection strings in the development Web.config file. In the deployed Web.config file, all the elements are removed.
<configuration xmlns:xdt="...">
<connectionStrings>
<add xdt:Transform="RemoveAll" />
</connectionStrings>
</configuration>
RemoveAttributes
Removes specified attributes from the selected elements.
Syntax
Transform="RemoveAttributes(comma-delimited list of one or more attribute names)"
Example
The following example shows how to select all the compilation elements in the development Web.config file. (Because there can be only one compilation element in the configuration file, you do not have to specify a Locator attribute.) In the deployed Web.config file, the debug and batchattributes are removed from the compilation element.
<configuration xmlns:xdt="...">
<compilation
xdt:Transform="RemoveAttributes(debug,batch)">
</compilation>
</configuration>
SetAttributes
Sets attributes for selected elements to the specified values. The Replace transform attribute replaces an entire element including all of its attributes. In contrast, the SetAttributes attribute enables you to leave the element as it is but change selected attributes. If you do not specify which attributes to change, all of the attributes that are present in the element in the transform file are changed.
The SetAttributes transform affects all selected elements. This is different from the Replacetransform attribute, which affects only the first selected element if multiple elements are selected.
Syntax
Transform="SetAttributes(comma-delimited list of one or more attribute names)"
Example
The following example shows how to select all the compilation elements in the development Web.config file. (Because there can be only one compilation element in the configuration file, you do not have to specify a Locator attribute.) In the deployed Web.config file, the value of the compilation element's batch attribute is set to false.
<configuration xmlns:xdt="...">
<compilation
batch="false"
xdt:Transform="SetAttributes(batch)">
</compilation>
</configuration>
Omitting Locator Attributes
Locator attributes are optional. If you do not specify a Locator attribute, the element to be changed is specified implicitly by the element that the Transform attribute is specified for. In the following example, the entire system.web element is replaced, because no Locator attribute is specified to indicate otherwise.
<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
<system.web xdt:Transform="Replace">
<customErrors defaultRedirect="GenericError.htm"
mode="RemoteOnly">
<error statusCode="500" redirect="InternalError.htm"/>
</customErrors>
</system.web>
</configuration>
Using Transform and Locator Attributes on Separate Elements
A Transform attribute does not have to be set in the same element as a Locator element. You can specify a Locator element on a parent element in order to select elements whose child elements you want to work with. You can then specify a Transform attribute in a child element in order to apply a change to the children.
The following example shows how to use the Locator attribute to select location elements for the specified path. However, only elements that are children of the selected location elements are transformed.
<configuration xmlns:xdt="...">
<location path="C:MySiteAdmin" xdt:Locator="Match(path)">
<system.web>
<pages viewStateEncryptionMode="Always"
xdt:Transform="SetAttributes(viewStateEncryptionMode)" />
</system.web>
</location>
</configuration>
If you specify a Locator attribute but you do not specify a Transform attribute in the same element or in a child element, no changes are made.
 Note |
|---|
|
A Transform attribute on a parent element can affect child elements even if no Transform is specified for them. For example, if you put the attribute xdt:Transform="Replace" in the system.web element, all the elements that are children of the system.web element are replaced with the content from the transform file. |
Community Additions
Config file is a big mistake
This system is way more complicated than it needs to be...
You guys need to simply this.
Have you guys took a look at rails framework. It automatically sets up debug, QA and dev environments.
Depending on which DB you are using you need to find the config file and set the server credentials.
This article puts me to sleep.
is there a way to add a comment?
Is there a way to add a comment to a customized web.config?
Example:
In web.prod.config:
<!--
Web.Config for the PRODUCTION server
-->
in web.QA.config:
<!--
Web.Config for the Q.A. server
-->
Thanks,
Marcelo
Is there way to do "InsertAtTop", basically the "Insert" add the node at the end, is there a way to
Is there way to do "InsertAtTop", basically the "Insert" add the node at the end, is there a way to add it as the first node?
InsertBefore isn't useful, as we may not know what's the current first node in source xml.
Web.Config transforms with new line symbol
<applicationSettings>
<ADM.Web.Admin.ADMSettings>
<settingname="ApplicationWebAddress"serializeAs="String">
<value>http://localhost:8929</value>
</setting>
</ADM.Web.Admin.ADMSettings>
</applicationSettings>Do transform:
<settingname="ApplicationWebAddress"serializeAs="String"xdt:Transform="Replace"xdt:Locator="Match(name)">
<value>http://live.site.com</value>
</setting>Get a config with new line character:
<settingname="ApplicationWebAddress"serializeAs="String">
<value>http://live.site.com
</value>
</setting>Anyone knows how to solve this issue?
Not all web.config elements have the "file" attribute
While it is true you can use the file attribute for appSettings instead, it is not true that you can use it for all elements. For instance, we write a log of WCF applications. The system.service.model element does not have a file attribute, and we must provide overrides to have diffent endpoints, bindings, etc. for different environment configurations.
The article is about how to write transforms. Using <appSettings> as an example is just an easy pedagogical technique, since everyone is so familiar with that element.
Preserve <CRLF> from the transform file?
It seems that the transform tool ignores, somewhat randomly, our <CRLF> characters between attributes. Is there a way to preserve them?
Or is there a way (particularly in a continuous build/deploy environment) to apply the formatting rules in Visual Studio for XML files to the generated output?
Managing elements with a different namespace
1) Add the (new) schema in question to the <configuration> element. For example:
<
configurationxmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform" xmlns:u="http://schemas.microsoft.com/practices/2010/unity">
2) In case you need to set an attribute on the alias tag within Unity, then use the following
<
u:unity>
<u:alias alias="yourAliasGoesHere"
type="yourTypeGoesHere"
xdt:Transform="SetAttributes"
xdt:Locator="Match(alias)"/>
</u:unity>
RE: Build with TFS
To use the web.config transformations you need to use a compatable web project and have it properly configured for each of your build configurations. For more information see: http://msdn.microsoft.com/en-us/library/dd483479.aspx
You can use TFS to build your web projects and it too can perform the web.config transformations. To do this you can include the following MSBuild command-line parameters /p:CreatePackageOnPublish=true /p:DeployOnBuild=True. If you are using TFS 2008 place each parameter on a separate line in the TFSBuild.rsp file. On build, you will get a new folder for your project package under the drop folder's _PublishedWebsites folder that contains your web deployment configuration package with the transformed web.config.
Transformation Test Tool
How to simply generate the Transformed Config
For testing your transformation or for a low-key transformation (avoiding a full publish of the project) you can add this custom task in your *.csproj
<UsingTask TaskName="TransformXml" AssemblyFile="$(MSBuildExtensionsPath)MicrosoftVisualStudiov10.0WebMicrosoft.Web.Publishing.Tasks.dll" />
<Target Name="Transform">
<MakeDir Directories="obj$(Configuration)" Condition="!Exists('obj$(Configuration)')" />
<TransformXml Source="Web.Config" Transform="Web.$(Configuration).config" Destination="obj$(Configuration)Web.config" StackTrace="true" />
</Target>
Afterwards you can generate the transformation using :
call "C:Program Files (x86)Microsoft Visual Studio 10.0VCvcvarsall.bat"
"msbuild" "D:SolutionsWeb.csproj" /m /t:Transform /p:Configuration=QA
Regards,
Jan Hebnes
XML Formatting may affect some application settings of type String
e.g.
<setting name="VersionDate" serializeAs="String">
<value>14th September 2010
</value>
</setting>
