It is my personal recommendation that you do three things:
Create fresh new Rails 3 app for yourself to “play around in” first. In fact, you don’t even need to play much, you just need to compare your existing config files to the config files in your brand new rails app. Moving the Gem version of Rails doesn’t change config settings, and most of the Rails 3 good stuff is in config settings (like the asset pipeline.) When they say “it works this way by default in Rails 3” – they DO NOT mean you will get that behavior automatically just by moving the Gem version – they mean that when you do “rails new xyz” the default configuration on your newly created app is set that way.
Don’t actually upgrade the existing repository. Instead, create a new Rails apps and copy files into it (Controllers, Views, Models, etc) one by one. This is more or less practical depending on your situation, so take this suggestion with a grain of salt. But if you do it this way, you can iteratively test as you make changes to confirm that each page and/or section of your app works.
Consider upgrading to 3.0.9 without the asset pipeline first. Then when you have it working in Rails 3.0.9, enable the asset pipeline (in application.rb) and move all the way up to Rails 3.2.1 (or whatever the latest is)
Beyond that, expect to have to:
Rewrite your routes.rb file (there’s a new syntax)
Change instances of <% form_for … %> to <%= form_for … %> in views
Change “named_scope” to “scope” in models
There’s also an official upgrade path, but I don’t even recommend that either. You’ll learn more about Rails 3 and become a better developer if you do it piece-by-piece, following suggestion #2 above.
I am working on a rails application I need to upgrade to the latest version
of Ruby and Ruby on Rails.
Make sure your automated test coverage is complete before you start,
then you can be reasonably confident, when you have finished, that all
is working.
I suggest you get your tests in gear if not already
get a core group (start with models, then controllers, minimum of models) passing in 2.3.5
then upgrade
you'll find a great number of plugins and gems will need to be upgraded - and some will have to be hand patched if you cannot find a suitable replacement
Jodi