Bundler.setup vs. Bundler.require

December 20, 2010

TL;DR Use Bundler.require instead of Bundler.setup

I think pretty much everyone knows that when you use Bundler with Rails 3, you don’t have to require your gems manually; it’s just all taken care of when you define them in the Gemfile. But I think a lot of people don’t understand exactly how this works, because when I see Bundler used outside of Rails, I consistently see gems being defined in the Gemfile and then manually required in the app.

I’m guessing this is because in the Bundler docs the most prominent example tells you to use Bundler.setup, and so people assume the auto-requiring is part of Rails and do this:

# Gemfile
source 'http://rubygems.org'

gem 'sinatra'
gem 'haml'

# config.ru
require 'rubygems'
require 'bundler'
Bundler.setup(:default)

require 'sinatra'
require 'sinatra/base'
require 'haml'

But actually it’s all Bundler. Instead of Bundler.setup you can call Bundler.require, which will not only set up the load paths but also require the gems as well. This is how Rails automatically requires the gems you specify. So the best way to do it (in most situations) is like this:

# Gemfile
source 'http://rubygems.org'

gem 'sinatra', :require => 'sinatra/base'
gem 'haml'

# config.ru
require 'rubygems'
require 'bundler'
Bundler.require(:default)

Note that you can specify a different name to require a gem by if the file name happens to be different from the gem name. And, as an added bonus, you can pass in multiple groups to Bundler.require, so you could also include gems specific to the current environment like this:

Bundler.require(:default, ENV['RACK_ENV'].to_sym)