Install and Create Rails 4.0 App

Rails 4.0 development has started a while back. It was merged into Rails’ master branch on Github in 2011. As the writing of this blog entry, the stable version of Rails is 3.2.8. Release candidate is at 3.2.9.rc1. Because 4.0 is not yet official available, you have to jump through hoops to get a Rails 4 application up and running.

Install Rails 4.0 gem

Create this Gemfile:

source 'http://rubygems.org'

gem 'rails', :git => 'git://github.com/rails/rails.git'
gem 'uglifier', '>= 1.0.30'
gem 'activerecord-deprecated_finders', :git => 'git://github.com/rails/activerecord-deprecated_finders.git'
gem 'journey', :git => 'git://github.com/rails/journey.git'

This Gemfile specifies the master branch of Rails, which contains 4.0 beta.
Gem activerecord-deprecated_finders is a dependency.
Gem journey, the Rails router, is also required.

In the same directory of the Gemfile, issue bundle install. This should install Rails 4.0.0.beta. But running gem list rails won’t show 4.0 being installed. So do this instead:

zlu@zlu-mba:~/projects/test$ bundle show rails
/Users/zlu/.rvm/gems/ruby-1.9.3-p0/bundler/gems/rails-4e23c0ef341c

The Rails executable is at:

`bundle show rails`/railties/bin/rails

`bundle show rails`/railties/bin/rails -v should show: Rails 4.0.0.beta

Now you can use this version of rails to generate an app named foo.

Create Rails 4.0 app

`bundle show rails`/railties/bin/rails new foo

This command creates a typical rails app called foo and output an error about not being able to find Rails 4 gem, which should not be a surprise.

You will edit foo/Gemfile to make bundle install work.

Add the two gems Rails depends on:

gem 'journey', github: 'rails/journey'
gem 'activerecord-deprecated_finders', github: 'rails/activerecord-deprecated_finders'

Change the source definition for the following gems:

gem 'rails', '4.0.0.beta'
gem 'sass-rails',   '~> 4.0.0.beta'
gem 'coffee-rails', '~> 4.0.0.beta'

gem 'rails', github: 'rails/rails'
gem 'sass-rails', github: 'rails/sass-rails'
gem 'coffee-rails', github: 'rails/coffee-rails'

Now you should be bundle install, sit back and enjoy your new Rails 4.0 app.