28 April 2010

Migrating ASP.NET MVC 1.0 to MVC 2.0: Real World Scenario

As most of you have noticed, ASP.NET MVC v.2.0 has been released last month. The new version introduces lots of cool features, so most of the existing MVC 1 applications will be upgraded to the new release. In the current post I will try to share my experience with migrating existing ASP.NET MVC 1.0 application to MVC 2.0.

Scenario: There is an existing ASP.NET MVC 1.0 web application build on top of .NET Framework 3.5, jQuery and Visual Studio 2008. The goal is to migrate the application to MVC 2, while keeping the other libraries and tools (.NET 3.5, VS2008, etc).

Identifying the breaking changes

The first step from the process would be to check the ASP.NET MVC 2.0 breaking changes. Naturally after carefully evaluating each item in the breaking changes list, I have find out that the following will be a problem: “JsonResult now responds only to HTTP POST requests”. The problem was caused by a jQuery plug-in that uses only HTTP GET. So the solution was to:

  • Replace the plug-in by someone more configurable that can use HTTP POST. You should do it in case that your application exposes sensitive information and is vulnerable to the attack described here.
  • Explicitly allow HTTP GET on JsonResults. You can do it by using the JsonRequestBehavior.AllowGet
public JsonResult GetData()
//Some other code
return Json(data, JsonRequestBehavior.AllowGet);

I was lucky that the information exposed in my application was not sensitive, so I decided to use the JsonRequestBehavior.AllowGet.

Migrating the solution to build against ASP.NET MVC 2.0

Being confident that I have resolved all breaking changes I had to think about migrating the solution to use the new version of MVC 2.0. If you don’t want to do everything by hand, you should use this tool. The tool is build by one of the Microsoft employees and works GREAT. However, I have noticed a few gotchas. The tool insists to backup your project before the conversion. This seems redundant, because usually the source code stays in code repository and if somehow the conversion produces a mess, everything could be restored. After all I had to wait a few extra minutes for the backup (more than 1GB in my case). The second issue that I have found is the update of the jQuery files. The tool updates the jQuery and Microsoft AJAX libraries. Since the web site was relying on several other 3rd party jQuery plug-ins I didn’t want the jQuery upgrade. So I had to manually remove the update. Despite of the above, the tool is absolutely FANTASTIC an you will need it.

Running the application

Up to now, everything went pretty well and the solution compiled without problems. So I was ready to run it. After hitting F5 I was stunned. The application started to close and open pages by itself! With the help of a few unit tests and Goolge I was able to identify the source of the problem. It turns out that there is another undocumented breaking change: a value from TempData dictionary will be removed after the request in which it is read! You can read more here. The fix was relatively easy and soon everything was working as usual.

Bottom line

The migration process from ASP.NET MVC 1.0 to MVC 2.0 is relatively easy and you should do it. The new features are awesome.