A better Config Store for SharePoint sites

I've recently made some enhancements to my Config Store framework on Codeplex which I'm now ready to share. Many of these enhancements are a result of adapting the solution to a large project where we built a platform for 80-100 internet sites - hence it's now become a bit more 'enterprise'. With such things I generally make a deal with my employer where I do the work (or most of it) in my spare time and then get to share the code publicly, so here we go. Before I delve into the details, let's have a reminder of what the Config Store is all about:

Recap - the SharePoint Config Store in a nutshell

Regular readers may remember this is a solution which allows use of a SharePoint list to store configuration values used by your SharePoint application - the idea is that your webparts/server controls/page layouts etc. store any strings/data they need for configuration in here as a more flexible alternative to web.config or similar. Since our values are now in a SharePoint list, configuration can be updated across the farm through the browser to administrators who have the appropriate permissions. We can also optionally take advantage of all the other things lists give us such as auditing, item-level security, alerts and version history etc. Finally, a caching layer is used to avoid round trips when your code fetches configuration values.

On the last couple of projects where my team has used it, we've finished up with 100+ config items in the list - storing all sorts of things from URLs, strings and 'application behaviour' switches:

If you need a more complete overview, see:

• http://www.sharepointnutsandbolts.com/2008/05/introducing-sharepoint-config-store-for.html
• http://www.sharepointnutsandbolts.com/2008/05/config-store-faqs.html

Enhancements in the new release

1. Optional "hierarchical" configuration model similar to web.config
   
   In the first release, since all the config values are stored in one list this means your configuration is stored in one 'nominated' site collection. This is fine for WCM sites which may only use one site collection, but may not easily map to certain enterprise requirements. What's new in this release is that the framework can now use a 'hierarchical' model, where a Config Store list exists in whatever site collections should have one, but a 'master' site collection is nominated which contains the 'master' config values. What happens is that if the config item you request is in the 'local' Config Store you'll get that value, and if not you'll get the value from the master list. This allows local overriding of the parent values if required - in practice we found 95% of the config items would be stored in the master list only, but having the facility to override the other 5% was critical to supporting some of the functionality we developed.
   
   Needless to say, this is the implementation which best suited our requirements. It could be it doesn't really suit yours, but developers could consider starting with my source code and modifying, since other aspects such as the caching layer, Feature files, event handlers etc. might not need to be changed much.
   
   If you want to continue to just use one Config Store list (even if you consume the config values in multiple site collections), the new code will continue to work just fine for this model too.
   
   
2. Easier to use in ASPX markup
   
   Similar to my recent Language Store framework, the Config Store now supports easily dropping values into ASPX markup by implementing an expression builder. So if all you want to do is set the Text property of a control, you can now do with this without cluttering up the code-behind. Or, as an alternative example, here we're retrieving an URL from the Config Store (stored in Category 'PageUrls' and key 'MyAccountPage') to assign to a hyperlink:

   <asp:HyperLink id="hyperlink1" NavigateUrl="<%$ SPConfigStore:PageUrls|MyAccountPage %>"
     Text="My account" ImageUrl="images/pict.jpg" runat="server"/>

   
   
   
   
3. Fixed caching bug for farm environments
   
   Yes, something I have to hold my hands up to here - the caching layer in the initial release didn't adequately deal with multiple servers. The effect was that it required an app pool recycle to pick up changes to config values, rather than them taking effect immediately. Not the end of the world, but certainly inconvenient and taking away some of the benefits of using a SharePoint list for configuration. So in this release, the implementation correctly relies on a back-end resource (using a CacheDependency) to invalidate the cache across all servers in the farm. The implementation I chose was to add the items to the cache with a CacheDependency on a text file - this needs to be located on a path which all servers can access - and the event handler now updates a timestamp in the file to invalidate the item in the cache across all servers.
   
   I went with using a file as the dependency item as I thought it was more lightweight than using a SqlCacheDependency - I didn't really want to impose the SQL configuration etc. to be able to use the Config Store. However, with the file cache dependency I've chosen, be aware that some production configurations may have internal firewalls which prevent all WFEs from accessing a shared file in this way - check before you deploy. Of course the code is there for you to modify should you wish to make changes in this area.
   


4. Amendment to Feature to prevent web.config modifications being made on Feature activation
   
   Another thing that got in the way when I tried to implement the Config Store on our enterprise project was the Feature event receiver which adds the required appSettings keys to web.config. The idea here is that, to help simplify installation and initial setup, the required web.config entries are added with empty values so all the developer has to do is plug in the appropriate values for his/her site. Sounds great - and it is for single site collection sites. But for multiple site collections, when we come to activate the Feature in the 2nd, 3rd, nth site collection - of course the receiver runs and adds the empty entries to web.config again, despite the fact that we'd already inserted the real values on the first activation. And since the new values come later in the file, guess which ones are used?
   
   So in this release there's a Feature property which determines if web.config modifications are made - it's set to 'False' by default but it's there if you prefer to change it.
   
   
5. 'Config value' column is now bigger
   
   Previously this column was a 'single line of text' but it's now a 'note'. This means you can happily store HTML/XML fragments or other larger values, which is very useful in some scenarios. However, note that if you're already using the Config Store on your site and want to 'upgrade', this schema change is significant - I discuss it in the readme.txt file.

So that's it. You can download the updates from www.codeplex.com/SPConfigStore - hope you find it as useful as we have.