Rails 3.0 beta is out and it’s now time to upgrade all the plugins available. To show you how to do it I’ve decided to create a small plugin compatible with Rails 2.x and Rails 3.0. It’s a wrapper around Rack::Cache to insert it automatically in a Rails application.

It’s a gem

First things first we create the gem we will name rails-cache. Thanks to Jeweler it’s dead easy. Just a few lines of code in a Rakefile and it’s done:

To create the VERSION file a echo "1.0.0" > VERSION is enough.

Rails 2.x way

The code of the gem will be in lib/rails/cache.rb and it’s just the insertion of the Rack::Cache middleware:

We build the gem with rake build and we install it with gem install --local pkg/rails-cache-1.0.0.gem. Then we need to load it in our environment.rb:

Rack::Cache is now plugged with the Rails application!

The new way

Rails 3.0 comes with Bundler. A cool thing with Bundler is that you can load a gem which have a custom path:

The :path option is the path to our gem. We have a lot of solution to do the same in Rails 2.x, with a plugin instead of a gem for example, but it is not as elegant as with Bundler (Bundler is usable with Rails 2.x).

To create a plugin for Rails there’s an object for that now, Rails::Railtie. So we just need to write an object which inherit from Rails::Railtie in lib/rails/cache.rb:

The gem has been upgraded to Rails 3.0!

Rails 2.x and 3.0 in a gem

This is just an example here, but it’s possible there’s a better solution:

And you can find the whole code on GitHub.

More about Plugins/Engines

• José Valim has written a draft documentation about Rails::Railtie, Rails::Engine and Rails::Application.
• Yehuda Katz has made a blog post about it.
• rails3_datamapper is a good example to see how to write a Rails 3.0 plugin.
• The latest commits for CarrierWave have been made to upgrade it to Rails 3.0.