I’m a lazy developer. Being lazy does not mean I avoid to work. It means that I like to reflect things I am doing and optimize and atomize stuff to get more time on the valuable tasks. Code generation is a tool I tend to use quite regularly and T4 is at most my generator of choice.

Generated files can cause a lot of merging conflicts. So they are not to be checked into my source control system (currently my choice is HG/Mercurial).

For the build server this means the files do not exist when the repository is freshly checked out – they need to be generated during the build right before the compile happens.

With code generation I usually tend to use a pattern that is for example also used by ASP.NET MVC Views/Controller generation: If there is a local directory containing code generation templates, use it. Otherwise utilize the system wide templates.

MsBuild version 4.0 comes with a feature called property functions. This allows to place for instance a “find directories” inside a property group.

I use them to:

  • Allow to set a system wide template directory using the command line/the MsBuild API.
  • If no directory is set use a local directory.
  • If non of the above is applied set a fallback default.

Here is the XML snippet that shows how to use the pattern:

 <?xml version="1.0" encoding="utf-8"?>
 <Project DefaultTargets="Generate" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
    <CodeGeneratorDir Condition=" '$(CodeGeneratorDir)' == '' " />
    <LocalCodeGeneratorDir> CodeGenerationTemplates </LocalCodeGeneratorDir>
    <CodeGeneratorDirFallback> C:\CodeGenerationTemplates </CodeGeneratorDirFallback>
    <ModelFiles Include="..\src\**\*.xdml" /> 
    <TemplateDirectory Include="$(CodeGeneratorDir);" /> 
    <TemplateDirectory Condition=" '$(CodeGeneratorDir)' == '' " Include="$([System.IO.Directory]::GetDirectories( &quot;$(RootFolder)&quot;, &quot;$(LocalCodeGeneratorDir)&quot;, System.IO.SearchOption.AllDirectories))" /> 
    <TemplateDirectory Condition=" '@(TemplateDirectory)' == '' " Include="$(CodeGeneratorDirFallback)" /> 
  <Target Name="Generate"> 
    <Message Text="@(TemplateDirectory)" /> 
    <Message Text="@(ModelFiles)" />