Config file XDT transformation InsertIfMissing is skipping children

Question

I am having trouble doing config transform, adding app settings on nuget package install where element appSetting may or may not exist.

What I want to happen:

• appSetting element does not exist
  • Insert appSetting element and its children
• appSetting element exist
  • Insert children if missing

I only get one or the other to work, but not both occasions.

web.config.install.xdt

<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
  <appSettings xdt:Transform="InsertIfMissing" >
    <add key="Swagger.Contact.Name" value="Some Name" xdt:Transform="InsertIfMissing" />
    <add key="Swagger.Contact.Email" value="[email protected]" xdt:Transform="InsertIfMissing" />
  </appSettings>
</configuration>

Example 1

web.config BEFORE

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.web>
    <compilation debug="true" targetFramework="4.5.2" />
    <httpRuntime targetFramework="4.5.2" maxRequestLength="51200" />
    <customErrors mode="Off" />
  </system.web>
</configuration>

appSettings element not present before transformation.

web.config AFTER

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.web>
    <compilation debug="true" targetFramework="4.5.2" />
    <httpRuntime targetFramework="4.5.2" maxRequestLength="51200" />
    <customErrors mode="Off" />
  </system.web>
  <appSettings>
    <add key="Swagger.Contact.Name" value="Some Name" />
    <add key="Swagger.Contact.Email" value="[email protected]" />
  </appSettings>
</configuration>

Example 2

web.config BEFORE

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.web>
    <compilation debug="true" targetFramework="4.5.2" />
    <httpRuntime targetFramework="4.5.2" maxRequestLength="51200" />
    <customErrors mode="Off" />
  </system.web>
  <appSettings>
    <add key="Other.Key" value="With Some Value" />
  </appSettings>
</configuration>

appSettings element present before transformation.

web.config AFTER

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.web>
    <compilation debug="true" targetFramework="4.5.2" />
    <httpRuntime targetFramework="4.5.2" maxRequestLength="51200" />
    <customErrors mode="Off" />
  </system.web>
  <appSettings>
    <add key="Other.Key" value="With Some Value" />
  </appSettings>
</configuration>

Nothing happens in example 2 as the appSettings element already exist, I would like it to still evaluate its child elements and insert those if they do not exist, but it seems they are just ignored. Is there any other value for the attribute xdt:Transform I can use, or any other hacks to work around this issue?

Answer 1

I had a similar problem quite a while back. The workaround I applied was to have two entries with <appSettings> in the XDT file, one to check if its absent and if yes, then go ahead and insert it. The other was for the scenario when the <appSettings> element was already present. Here is short snippet to help you with your problem:

<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
    <appSettings xdt:Transform="InsertIfMissing">
    </appSettings>
    <appSettings>
      <add key="Swagger.Contact.Name" value="Some Name" xdt:Transform="InsertIfMissing" />
      <add key="Swagger.Contact.Email" value="[email protected]" xdt:Transform="InsertIfMissing" />
    </appSettings>
</configuration>

Let me know if this works for you.