How to add config transformations for a custom config file in Visual Studio?

Visual Studio transforms only web.config files by default.

If you need custom config file with transformation for DEV, UAT, PROD, etc environments, then try to

1. Use custom extensions for Visual Studio like SlowCheetah - XML Transforms for Config transformation preview functionality.
2. Add for the project from Nuget SlowCheetah to provide build in transformation.

A little bit details:

Add VS Extension SlowCheetah from Extensions and Updates

Right click on your myconfig.config and choose add transorm:

Inside each defined configurations insert your own transormation rulles like that:

<services xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
  <service name="WebApplication1.Services.Service2" xdt:Transform="Replace" xdt:Locator="Match(name)" >
    <endpoint address="http://localhost:57939/Services/DebugService" behaviorConfiguration="WebApplication1.Services.Service2AspNetAjaxBehavior"
      binding="webHttpBinding" contract="WebApplication1.Services.Service2" />
  </service>
</services>

Hope it was helpful

I'm going to extend on Andoni Ripoll Jarauta's answer a little.

We were faced with a similar problem. I wanted to pull the connection strings out of the web.config file to limit merge conflicts. I also wanted create a "release" config containing static information when publishing.

...simple enough. Create a custom config file, webdb.config, and update the web.config file.

Ex. web.config

<connectionStrings configSource="WebDB.config"/>

wedbdb.config (xml version="1.0" is required for transformation)

<?xml version="1.0" encoding="utf-8"?>
<connectionStrings>
</connectionStrings>

Next add transformation files for webdb.config

WebDB.Debug.config example:

<?xml version="1.0" encoding="utf-8"?>

<connectionStrings xdt:Transform="Replace" xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
    <add name="PRRADDataContainer" connectionString="metadata=~/PRRADData.csdl|~/PRRADData.ssdl|~/PRRADData.msl;provider=System.Data.SqlClient;provider connection string=';Data Source=localhost;Initial Catalog=;User ID=;Password=;multipleactiveresultsets=True;App=EntityFramework';" providerName="System.Data.EntityClient" />
    <add name="MyConnectionString" connectionString="Data Source=localhost;Initial Catalog=;Persist Security Info=True;User ID=;Password=;" providerName="System.Data.SqlClient" />
</connectionStrings>

WebDB.Release.config example:

<?xml version="1.0" encoding="utf-8"?>

<connectionStrings xdt:Transform="Replace" xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
    <add name="PRRADDataContainer" connectionString="metadata=~/PRRADData.csdl|~/PRRADData.ssdl|~/PRRADData.msl;provider=System.Data.SqlClient;provider connection string=';Data Source=prod_server;Initial Catalog=;User ID=;Password=;multipleactiveresultsets=True;App=EntityFramework';" providerName="System.Data.EntityClient" />
    <add name="MyConnectionString" connectionString="Data Source=prod_server;Initial Catalog=;Persist Security Info=True;User ID=;Password=;" providerName="System.Data.SqlClient" />
</connectionStrings>

Next we need to add an after-build event. This is created by simply editing the CSPROJ file.

<UsingTask TaskName="TransformXml" AssemblyFile="$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)\Web\Microsoft.Web.Publishing.Tasks.dll" />
<Target Name="AfterBuild">
    <TransformXml Source="WebDB.config" Transform="WebDB.$(Configuration).config" Destination="WebDB.config" />
</Target>

Now when I run locally I'll get WebDB.Debug.config and when I publish my code I just need to make sure to select "Release" as the configuration source. In both cases the WebDB.config file will be updated with the corresponding file when you build.

NOTE: make sure you set the webdb.config, webdb.debug.config, and webdb.release.config to "Do not copy" for the "Copy to Output Directory" option.

Hope this helps!

I have been using SlowCheetah but I found something that I think is more elegant. Just telling to the build to generate the .config depending on the build configuration.

Having a app.Release.config in your project (or many more depending on you deployment needs) you just need to edit the project file (the .csproj one if you program in C#). Find the end of it, between the last </ItemGroup> and </Project> and add:

  </ItemGroup>
  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
  <UsingTask TaskName="TransformXml" AssemblyFile="$(MSBuildExtensionsPath32)\Microsoft\VisualStudio\v$(VisualStudioVersion)\Web\Microsoft.Web.Publishing.Tasks.dll" />
  <Target Name="AfterBuild">
    <PropertyGroup>
      <OutputTypeName>$(OutputType)</OutputTypeName>
      <OutputTypeName Condition="'$(OutputTypeName)'=='Library'">dll</OutputTypeName>
      <OutputTypeName Condition="'$(OutputTypeName)'=='Module'">dll</OutputTypeName>
      <OutputTypeName Condition="'$(OutputTypeName)'=='Winexe'">exe</OutputTypeName>
    </PropertyGroup>
    <TransformXml Source="Config\app.config" Transform="Config\app.$(Configuration).config" Destination="$(OutputPath)\$(AssemblyName).$(OutputTypeName).config" />
  </Target>
</Project>

Save and reload from VisualStudio. Compile in Release mode and check the bin/Release folder on your <MyProject>.config file the transformation is done.

This example applies to Exe and Dll files and any VisualStudio version because includes this post help