How to easily use Rails 3 now

gem uninstall bundler
gem install tzinfo builder memcache-client rack rack-test rack-mount 
gem install erubis mail text-format thor bundler i18n
gem install rails --pre

Now that rails 3 is getting closer to release, I wanted to start playing around with it. I've seen a few articles on getting it up and running, but they all seemed a little bit complicated. To use rails 2.3.5 before its release, I just built the gems myself and installed them. It turns out you can easily do the same with rails 3.

First, install rails main dependencies:

gem install rake rack bundler
gem install arel --version 0.2.pre

Next, get the latest rails code from github, and install the rails gems. There may be a few errors you can safely ignore:

git clone git://github.com/rails/rails.git
cd rails
rake install

And bang, you can start your first rails 3 project:

rails ~/apps/playground/rails3 

Your existing projects shouldn't be affected as rails is installed as a prerelease gem, but to be safe I'd recommend a tool like rvm to switch to a clean set of gems.

Tip: Relative paths with File.expand_path

You probably know about the __FILE__ magic constant. It holds the filename of the currently executing ruby source file, relative to the execution directory. So with the following saved as /code/examples/path_example.rb:

puts __FILE__

Running this file from the /code folder will output examples/path_example.rb

This is often used to load files on paths relative to the current file. The way I've used it before is like this:

config_path = File.expand_path(File.join(File.dirname(__FILE__), "config.yml"))

This works, but it's a bit clunky.

What I didn't realise until reading the rails source code the other day, is that File.expand_path can take a second argument - a starting directory. Also, this argument doesn't actually have to be a path to a directory, it also accepts a path to a file. With this knowledge we can shorten the above to the following:

config_path = File.expand_path("../config.yml", __FILE__)

Much simpler.