1. Rails Engines - what, why, how
Grzegorz Witek

2. Agenda
• What engines are
• How they appeared in Rails core
• How to use them
• What are their pros and cons
• Summary

3. What engines are
Application
Engine
Plugins

4. What are their capabilities?
Rails engines have:
Rack middleware stack

5. What are their capabilities?
Rails engines have:
environment.rb

6. What are their capabilities?
Rails engines have:
Routes

7. What are their capabilities?
Rails engines have:
Plugin support

8. Long way to the CORE
• Plugin
• Rails 2.3 - partial support
• 2010 Ruby Summer of Code
• Rails 3.1 - full engines in core
• ...
• 2011? - a few apps in the same process

9. A bit of code
Rails.application.routes.draw do mount Cms::Engine => "/portal", :as
=> 'cms' end
main_application.root_pathcms.articles_path
rake railties:copy_migrations
authenticate :admin do
mount Tolk::Engine => "/tolk" end

10. Are they really worth using?
Pros:
• they are almost as
powerful as rails app
• they are isolated (you don't
need to change your code
to use them!)
• You can share code
between applications
• they can save your time!
Cons:
• they're not suitable for
every application

11. Do they exist?
• Devise
• Rails Admin
• Rails Assets (to be released in 3.1)
• Tolk

12. Any questions?
Thanks for your attention!

13. Sources:
• http://piotrsarnacki.com
• https://github.com/dhh/tolk
• http://rails-engines.org/
• http://railscasts.com/episodes/149-rails-engines
• http://github.com/sferik/rails_admin
• https://github.com/lazyatom/engines
• https://github.com/rails/rails