\I receive a lot of questions regarding web.config transforms, which have existed in Visual Studio since 2010, and wanted to clear up the support that we have in this area. These transforms show up in the solution explorer underneath web.config as shown in the image below.
Since the names of these transforms include the build configuration many people expect that web.config will be transformed when they start debugging (F5) or run the app (CTRL+F5) in Visual Studio. But sadly this is not the case. These transforms are kicked in only when the web is packaged or published. I totally agree that this would be awesome, and I even blogged about how to enable it at http://sedodream.com/2010/10/21/ASPNETWebProjectsWebdebugconfigWebreleaseconfig.aspx. It may seem like it would be really easy for us to include this support in the box, but unfortunately that is not the case. The reason why we are not able to implement this feature at this time is because a lot of our tooling (and many partners) relies on web.config directly. For example when you drag and drop a database object onto a web form, it will generate a connection string into the web.config. There are a lot of features are like this. It is a significant investment for us to make a change of this level. We were not able to get this done for Visual Studio 11, but it is on our radar and we are looking to see what we can do in this area in the future.
Sayed Ibrahim Hashimi @SayedIHashimi