Invoking app/web.config File Transformations on Build

MSBuild provides the functionality to generate a production web.config (or app.config) from the developer’s web.config merged with a web.*.config transformation file named after the current Configuration. This web.config File Transformation is applied when you Deploy a (web) application.

But what if you want to apply the same file transformation during build? The scenario occurs if a team checks in the web.config file, but needs customization for each developer of the team (e.g. different local SQL connection strings, log directories etc).

Digging through the various .targets files that configure the VS build system, I found a reference to the <TransformXml> command in Microsoft.Web.Publishing.targets deep inside the Visual Studio installation directory. (see the answers on this SO question)

Putting it all together, I came up with an AfterBuild step in the .csproj file which applies the web.config transformation on build, rather than on deploy:

  <Target Name="AfterBuild">
	<TransformXml Source="web.common.config"
	        Transform="web.onbuild.config"
	        Destination="web.config" />
  </Target>

(add the parameter $(Configuration) where necessary.)