Nuget Package - Web.config.transform Add - asp.net

Question

I'm creating a NuGet package and want it to update the web projects Web.Config file with certain settings. I am using the web.config.transform to edit the web.config file of an application. It's working well when I simply add appSettings - like so:
<configuration>
<appSettings>
<add key="WebPToolFolder" value ="~/Tools"/>
<add key="ImagesFolder" value ="~/Content/themes/base/images"/>
</appSettings>
</configuration>
However, if I try an add to the staticContent it doesn't seem to alter the tags. For example, here is the web.config.transform file:
<configuration>
<appSettings>
<add key="WebPToolFolder" value ="~/Tools"/>
<add key="ImagesFolder" value ="~/Content/themes/base/images"/>
</appSettings>
<system.webServer>
<staticContent>
<mimeMap fileExtension=".webp" mimeType="image/webp" />
</staticContent>
</system.webServer>
</configuration>
It updates the appSettings, but not the staticContent tags - any ideas?

Answer 1

Old question but if anyone lands on it the following should work:
In your case to add/update the staticContent element:
It's an alternative solution, so you won't use the .transform file, but rather the web.config.install.xdt (and web.config.uninstall.xdt) which I find better:
<?xml version="1.0"?>
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
<!-- some other elements -->
<staticContent xdt:Transform="InsertIfMissing">
<mimeMap fileExtension=".webp" mimeType="image/webp" xdt:Locator="Match(fileExtension)" xdt:Transform="InsertIfMissing" />
</staticContent>
<!-- some other elements -->
</configuration>
This way you don't need to do any pre-update preperations, just upgrade the package.
Check this post for XDT support from Nuget 2.6 onwards.

Answer 2

You need to put an empty <staticContent></staticContent> in your web.config and then use the xdt:Transform="Insert" on the element like this:
Your web.config:
<configuration>
<appSettings>
<add key="WebPToolFolder" value ="~/Tools"/>
<add key="ImagesFolder" value ="~/Content/themes/base/images"/>
</appSettings>
<system.webServer>
<staticContent>
</staticContent>
<system.webServer>
</configuration>
And then you can insert a value in your transform file like this:
<system.webServer>
<staticContent>
<mimeMap fileExtension=".webp" mimeType="image/webp" xdt:Transform="Insert"/>
</staticContent>
</system.webServer>
Took me a while to find out. Hope this helps.

Answer 3

Have you tried adding an xdt:Transform="Replace" attribute to the tags you want to update?
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
<appSettings>
<add key="WebPToolFolder" value ="~/Tools" xdt:Transform="Replace"/>
<add key="ImagesFolder" value ="~/Content/themes/base/images" xdt:Transform="Replace"/>
</appSettings>
<system.webServer>
<staticContent>
<mimeMap fileExtension=".webp" mimeType="image/webp" xdt:Transform="Replace"/>
</staticContent>
</system.webServer>
</configuration>
There's some good Microsoft documentation here
If you post the initial markup and what you want it to look like maybe we could help a bit more :)