Don't you just love those days when you come to work full of energy and ideas, ready to have a productive day only to be stumped by a seemingly simple problem that ends up wasting the entire day? Today was one of those days. My only consolation is that this blog post reports the solution, hopefully saving some other poor soul their time and their sanity.

The need was simple. Write out connection strings to the app.config file of an application and encrypt them. Sound easy? Sure. There are lots of examples out there about how to do this, but there's a problem no one seems to mention. You can't just update a config file at runtime and expect those changes to stick. I ran into that problem the other day and solved it here. But there's a more sinister problem. Let me explain.

First, here's what I'm doing:

I have an array of connection strings (as strings) from an external service that I want to add to the app.config file of the current application. I write them out to the <connectionStrings> section and then save the file, taking care to make sure I tell the System.Configuration.ConfigurationManager to refresh the section, meaning it should reload the section from disk the next time it's accessed.

When this happens further along in the program on this line ...

          ConnectionStringSettings
dbConn = System.Configuration.ConfigurationManager.ConnectionStrings[DefaultDatabaseKey]; 
        

... I get this error message:

Unrecognized attribute 'configProtectionProvider'.

I did the usual searches and came up with no solutions. Some folks suggested loading two AppDomains, restarting the app, etc. I can't believe you'd have to restart an app just to pick up configuration changes! After all, I can to this now. The problem comes when I try to encrypt the section.

When you successfully encrpyt a section, a new attribute "configProtectionProvider" is added to the <connectionStrings> element. It appears that when ConfigurationManager tries to reload this section, it can't digest this new attribute.

Okay, let's just get to the solution before I waste even more of my day...

The answer turned out to be simple. Instead of telling ConfigurationManager to refresh the "connectionStrings" section, have it refresh the next level up which would be the <configuration> section itself:

Oh happy day.

I was running into a problem when trying to modify the app.config file for an application at runtime. Specifically, I was adding connection strings to the <connectionStrings> section but further along in my code the changes were not visible. However, the configuration file was changed! How could this be? After much head scratching and research, I find the problem.

To change the app.config file I was opening the config file like this:

I then add or update individual connection strings as need (that code's not important). Finally, I save the changes:

Further on in the code I then attempt to access the connection strings, but instead I use the ConfigurationManager class like this:

Intellisense is wonderful. It's so useful it's actually scary because it doesn't force you to remember a lot class names, enum values, etc. This is good for productivity but bad when you need to recall something without the Visual Studio IDE!

In any case, I like to get Intellisense whenever I can. One area that I kept putting off was adding Intellisense for custom configuration sections I create. I dislike loads of <add> tags in the <appSettings> section because it becomes hard to navigate. I prefer to create custom config sections. However, I don't get the benefit - out of the box - of Intellisense and schema validation. To get this, you need to create your own XSD file to support your custom config sections.

XSDs for config sections are not hard to write. In fact, its best to just take a look at the XSD file for the .NET config file which can be found in your Visual Studio installation folder. For example, on my machine for VS 2008, I navigate to:

C:\Program Files\Microsoft Visual Studio 9.0\Xml\Schemas

Here you'll find loads of XSD files for all sorts of things. The most important one however is called DotNetConfig.xsd. This contains the schema definitions for the base .NET config file. There are also supplimental files for .NET 2.0 and 3.0 config sections in DotNetConfig20.xsd and DotNetConfig30.xsd respectively.

Here's a simple example of a config section:

The xsd schema (MyConfig.xsd) for this config section is:

I placed this file in the ...\Xml\Schemas folder in the Visual Studio installation folder as noted above. Now, to hook this into VS, you need to add it to the xsd catalog. You do this by editing the file catalog.xml. Add the following line to the bottom of this file before the closing <schemaCatalog> tag:

  <Association extension="config" schema="%InstallRoot%/xml/schemas/MyConfig.xsd" condition="%TargetFrameworkVersion% != 2.0 and %TargetFrameworkVersion% != 3.0" />

That's it! Now when you go into VS and edit a config file, you'll get Intellisense!