I’ve been playing with Visual Studio 2010 Beta a little and one of my favorite new features (and there are many) is the new web.config transformation feature.
Web.config transformations are setup so there is one configuration “delta” for each build configuration that you have (default are Debug and Release). When you build your solution (as a package, when you publish, etc) your original web.config is transformed according to the settings in your web.debug.config file (assuming the debug configuration).
There are plenty of blogs and msdn references out there for you to look at but I thought I’d write a quick post that would get you up to date on how to do the some common web.config transformations.
First, A Tiny Iota (That guy was great!) of XDT Review
As it pertains to web.config replacements, you need to know that every XML element can have two xdt attributes: xdt:Tranform and xdt:Locator
- Transform: What you want to do with the XML element
- You might want to Replace it, set an attribute (SetAttribute), remove an attribute (RemoveAttribute), etc.
- Locator: Where is the element that needs transformation?
- You probably want to transform an element that matches (Match) a specific attribute value
Case 1: Replacing all AppSettings
This is the overkill case where you just want to replace an entire section of the web.config. In this case I will replace all AppSettings in the web.config will new settings in web.release.config. This is my baseline web.config appSettings:
Now in my web.release.config file, I am going to create a appSettings section except I will include the attribute xdt:Transform=”Replace” since I want to just replace the entire element. I did not have to use xdt:Locator because there is nothing to locate – I just want to wipe the slate clean and replace everything.
Note that in the web.release.config file my appSettings section has three keys instead of two, and the keys aren’t even the same. Now let’s look at the generated web.config file what happens when we publish:
Just as we expected – the web.config appSettings were completely replaced by the values in web.release config. That was easy!
Case 2: Replacing a specific AppSetting’s value
Ok, so case 1 was the nuclear option, what about doing something a little more practical? Let’s go back to our original AppSettings web.config example:
Let’s say that we just want to replace KeyB’s value to something more suited for a production environment. This time we get to use both xdt:Transform and xdt:Locator.
Our strategy will be to define (in web.release.config) an appSettings section that has just the replacements we want to make. It will initially look like this:
Now we want to add in the transforms so that we replace any appSetting that matches this key (KeyB).
Once we publish our resulting web.config file looks like this:
Perfect – We replaced KeyB but left KeyA (and any other keys if they were to exist) alone.
Case 3: Replace Compilation Debug=”true”
This is a simple one because Microsoft gives it to us out of the box – but I’ll reproduce it here anyway because it illustrates a common scenario and shows that there are more transforms then just Replace:
There are also ways to SetAttributes, Remove elements, Insert elements, and much more
To Infinity – And Beyond
We have obviously just scratched the surface, but for now that’s as deep as I need to go. Until next time, you can look at the MSDN reference for Web.Config transformations at http://msdn.microsoft.com/en-us/library/dd465326%28VS.100%29.aspx.