It's been an interesting week for me. I got a first-hand taste on upgrading a Rails 1.2.x application to Rails 2.0. To be honest, I was terrified when this task was presented upon me. I had never done this before, since virtually all the Rails 2.0 (and 2.1) apps I've worked with have started with that particular version, not an upgrade. Seeing that the application in question had been under development for a long time (hence still using Rails 1.2), I immediately though that an upgrade to Rails 2.0 would cause the app to break so bad, I would be having "NoMethodError" messages in my nightmares for a long time to time.

So with the thought of a long week of fixing trivial changes to make the application work correctly once again, I removed the frozen Rails 1.2 directory from the application and froze Rails 2.0 in its place. I started Mongrel, and... It worked. Like it really worked. Well, not 100%, but most of the application worked as it was before! I definitely couldn't believe it. That was probably the easiest framework upgrade I've done in my entire life. Most of it had to do because of me doing a lot of refactoring for code that I had knew would be removed from the framework soon, but also kudos to the Rails Core team for making this pretty straightforward.

Like I said, it didn't go 100% smoothly, so I thought I'd share some of the gotchas I encountered during the upgrade.

'extract_options_from_args!' method

The extract_options_from_args! method was apparently removed in Rails 2.0. Upon further inspection, there were many plugins using this method, but only one (nested_has_many_though) wasn't properly handling it. All I had to do was update that particular plugin, and the error disappeared from the entire application. So my recommendation is to upgrade any currently existing plugins you have, although this is more tricky if you have old plugins that aren't being currently maintained.

'You are being redirected' problem

In some places of the application, when an action used 'redirect_to' to send me somewhere else, a page would appear, simply saying 'You are being redirected', with a link to where the app should've been redirected. The problem: there was a parameter named 'status' that was used for the redirect. Changing the parameter name to 'state' solved the problem. I'm guessing it's because Rails uses the word 'status' to set the HTTP code for a redirect, so it caused this hiccup.

'Called id for nil' error

I was also getting errors for nil variables where they didn't exist before. The problem here was caused because some 'form_for' tags were using variables that weren't initialized previously in the controller. Taking for example the following code: <% form_for @item, :url =>items_path do |f| %>. The instance variable '@item' wasn't declared in the controller (or the view, although if someone did that, I would hunt them down), yet in Rails 1.2 it would work properly. It was just a matter of adding @item = in the controller for the action, and it would work fine again. I guess this was just done to make sure things are coded correctly, which I really don't mind.

Route Globbing and escaped slashes in URL

This one was an interesting one. Part of the application uses route globbing, where you can set a route to grab everything in a URL and set an array. The application in question was using this in one part of the application, to get a collection of IDs and process them for some other functionality. However, this was being done via a link generated using 'link_to', which promptly went to escape the slashes between the IDs (from '/' to '%2F', which the browser read well, but Rails 2.0 apparently doesn't like), and the route globbing wouldn't return the array as expected. For example, previously in Rails 1.2, if the URL ended like items/process/101/105/110, the route globbing would return an array of three elements: ["101", "105", "110"], which is what the app expected. In Rails 2.0, since the slashes were escaped thanks to 'link_to', it would return an array of one single element: ["101/105/110"]. This problem was already reported and seems like it'll be fixed in Rails 2.1.1. But in the meantime I did a quick fix: take the element in the array and split it using Ruby's split method to create the array as it should be before processing.

Besides these errors, the rest went smoothly. The app has been running for two days under moderate testing, and nothing else appears to be broken. So it all went well. Hope this post helps someone get through some problem upgrading their old, creaky Rails app.