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<< Bundler | README | Default Initializers >>

Chapter 10. Startup Scripts

Whenever you start a process to handle requests with Rails (like rails server), one of the first things that happens is that config/boot.rb is loaded.

There are three files involved in setting up the entire Rails stack.

config/environment.rb

This file loads application.rb, and then runs initializer scripts.

# Load the Rails application.
require_relative 'application'

# Initialize the Rails application.
Rails.application.initialize!

config/boot.rb

This file is required by application.rb to set up Bundler and load paths for Rubygems.

ENV['BUNDLE_GEMFILE'] ||= File.expand_path('../Gemfile', __dir__)
require 'bundler/setup' # Set up gems listed in the Gemfile.

Note: Bundler.setup will add all your gems to the Rails load path but won't actually require them. This is referred to as a "lazy-loading" setup. See the Rails Class Loader section for more info.

config/application.rb

Now we get into the meat of configuration. This script loads the Ruby on Rails gems and gems for the specified Rails.env and configures the app. Changing these items require a server restart to take effect.

require_relative 'boot'

Note that the boot script is generated as part of your Rails app, but you don't usually need to edit it.

Next, the Rails gems are loaded.

require 'rails/all'

By replacing this line you can easily cherry-pick only the components needed by your app:

# To pick the frameworks you want, remove 'require "rails/all"'
# and list only the framework railties that you want:
#
# require "active_model/railtie"
# require "active_record/railtie"
# require "action_controller/railtie"
# require "action_mailer/railtie"
# require "action_view/railtie"
# require "sprockets/railtie"
# require "rails/test_unit/railtie"

The main config of our app follows, which gets it own module and class:

module TimeAndExpenses
  class Application < Rails::Application
      # Settings in config/environments/* take precedence over those
      # specified here. Application configuration should go into files
      # in config/initializers
      # -- all .rb files in that directory are automatically loaded.

Note: The creation of a module specifically for your app lays a foundation for running multiple Rails apps in the same executable Ruby process.

<< Bundler | README | Default Initializers >>