Engines Lightning Talk

The Rails
Engine That
Could?
Saturday, April 28, 2012

Hi!
www.launchware.com
on the InterTubes

Hiring

dpickett
on Twitter


What I Can Tell You
About Rails Engines
• A Brief History
• A Rails Engine In Rails 3.1
• Implementation Gotchas
• Deployment Gotchas With Heroku
• Conclusions

Out With The Old...
• Components in Rails
Beta and Rails 1

• Components
removed in Rails 2


...In With the New

• Engines in Rails 3
• Enginex as part of Rails 3.1


Generating

rails generate plugin thomas --mountable


Manage Dependencies
In Your Gemspec

Shift Your Perspective


Shifting Perspectives

• Think like an API designer
• Favor composition over inheritance
• Obey SOLID principles for more
maintainable code


Maintain Perspective

• Do as you would normally:
• Write migrations
• Seed data
• Run rake tasks
• Run generators


Gotchas


Routes

• Routes are loaded where you mount
them
• Only one opportunity for placement
• No ﬂexibility to divide up routes for
ﬁne tuning priorities


Namespacing
• Namespace Your Engine - it will save you lots of
pain.
• If you must in your consuming application, use
ActiveSupport’s require_dependency to override:
require_dependency
Thomas::Engine.root.join(“app/models/user”).to_s

class User < ActiveRecord::Base
#override the engine here
end


Consumer::Application do
Thomas::Routes::UserRoutes.draw(self)
#custom routes here
Thomas::Routes::ScheduleRoutes.draw(self)
end

module Thomas
module Routes
module UserRoutes
def self.draw(map)
map.instance_eval do
resources :user...
end
end
end
end
end

Named Routes Helpers

• If you don’t namespace, I found these to be
incredibly problematic
• You must include helpers in your
application controller and in your request
specs/tests


class ApplicationController < ActionController::Base
include Thomas::Engine.routes.url_helpers
include ActionDispatch::Routing::PolymorphicRoutes
end

You’ll use these two lines a lot.

Apply when you get an undeﬁned *_path or *_url
method


Devise
• Wiring I18n load paths is deferred until the
app comes up, disallowing override ability


class Thomas::Engine < Rails::Engine
config.after_initialize do
Rails.application.config.after_initialize do
paths = I18n.load_path.delete_if do |p|
p =~ /devise-/
end

#put devise’s default locales in its place
I18n.load_path = paths + I18n.load_path
I18n.reload!

end
end


Inherited Resources
And Responders
Doesn’t Work
Drops Your Responder


Wrong Thomas...
...Go B’s


class ApplicationController < ActionController::Base
def self.engine_inherit_resources
inherit_resources
self.responder = MobileResponder
end
end
end


Deploying Private
Gems To Heroku
• Bundle with your github credentials in
plaintext
• Maintain your own gem server
• Write a rake task to vendor the gem and
commit when deploying
• NEW: http://www.gemfury.com/


Overall, Engines Are
Great
• There’s still room for
improvement, but they’re
awesome once you get
going
• They will challenge you as
a developer and as a Rails
Framework user


Thanks!

• I’ll post slides @ www.launchware.com
• Chat me up on Twitter: @dpickett
• Chat me up on IRC: dpickett in #boston.rb
• We’re hiring!


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