This is a presentation about what Rails Engines are for the RubyGDL group talks

1. Rails Engines
!
@igmarin

2. Rails Engines
• Engines are stand-alone Rails application that can
be mounted inside of another application
• Controllers and Models are defined within
modules of the engine’s namespace
• architecting an app with engines forces you to
really think through your dependencies and
makes you isolate things from the get go

3. Big Plus
• Reduce errors from duplication
• Reusable code

4. Generate Rails Engine
we have a rails new plugin generator that will help us

5. $ rails plugin new awesome
creates a skeleton for
developing any kind of Rails
extension with ability to run
tests using dummy Rails
application
awesome
|-- Gemfile
|-- Gemfile.lock
|-- MIT-LICENSE
|-- README.rdoc
|-- Rakefile
|-- awesome.gemspec
|-- lib
| |-- awesome
| | `-- version.rb
| |-- awesome.rb
| `-- tasks
| `-- awesome_tasks.rake
`-- test
|-- awesome_test.rb
|-- dummy

6. $ rails plugin new awesome --full
--full tells that we want an
engine including app:
• An app directory tree
• An a config/routes.rb
awesome
|-- Gemfile
|-- Gemfile.lock
|-- MIT-LICENSE
|-- README.rdoc
|-- Rakefile
|-- app
| |-- assets
| |-- controllers
| |-- helpers
| |-- mailers
| |-- models
| `-- views
|-- awesome.gemspec
|-- bin
| `-- rails
|-- config
| `-- routes.rb
|-- lib
| |-- awesome
| | |-- engine.rb
| | `-- version.rb
| |-- awesome.rb
| `-- tasks
| `-- awesome_tasks.rake
`-- test
|-- awesome_test.rb
|-- dummy

7. lib/awesome/engine.rb
module Awesome
class Engine < ::Rails::Engine
end
end

8. $ rails plugin new awesome --mountable
namespace-isolated engine.
Same as full
• Asset manifest files (application.js and
application.css)
• A namespaced ApplicationController stub
• A namespaced ApplicationHelper stub
• A layout view template for the engine
awesome
|-- Gemfile
|-- Gemfile.lock
|-- MIT-LICENSE
|-- README.rdoc
|-- Rakefile
|-- app
| |-- assets
| |-- controllers
| |-- helpers
| |-- mailers
| |-- models
| `-- views
|-- awesome.gemspec
|-- bin
| `-- rails
|-- config
| `-- routes.rb
|-- lib
| |-- awesome
| | |-- engine.rb
| | `-- version.rb
| |-- awesome.rb
| `-- tasks
| `-- awesome_tasks.rake
`-- test
|-- awesome_test.rb
|-- dummy

9. lib/awesome/engine.rb
module Awesome
class Engine < ::Rails::Engine
isolate_namespace Awesome
end
end
test/dummy/config/routes.rb
Rails.application.routes.draw do
mount Awesome::Engine => "/awesome"
end

10. Route Helpers
awesome.root_url # /awesome
!
main_app.root_url # /

11. Generators
lib/generators/awesome/install_generator.rb
!
module Awesome
class InstallGenerator < Rails::Generators::Base
def install
run ‘bundle install’
route “mount Awesome::Engine => ‘/awesome’”
rake ‘awesome:install:migrations’
rake ‘db:migrate’
end
end
end

12. Popular Engines
• Devise —> Authentication
• Spree —> e-Commerce
• Forem —> Forum
• RailsAdmin —> Admin Interface
• Monologue —> Blogging

13. Resources
• Great Book: Multitenancy on Rails by Ryan Bigg
• https://www.youtube.com/watch?v=s3NJ15Svq8U
• http://guides.rubyonrails.org/engines.html
• http://tech.taskrabbit.com/blog/2014/02/11/rails-4-
engines/
• http://gaslight.co/blog/maintainable-and-scalable-
systems-with-rails-engines