Rails Engines - Lessons Learned

Saturday, 3 March 12

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How my
curiosity
about new
features in
Ruby on Rails...

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...
kind of
sort of...

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...indirectly led me to
getting a new job...

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...where I do
awesome
“stuff”...

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...for an
awesome
community...

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...and exactly what
that awesome
“stuff” entails.

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aka
“Namespacing: Good for
the soul”

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Ryan
Bigg

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Ryan
Bigg
@ryanbigg

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Ryan
Bigg
Radar
@ryanbigg

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26,890
reputation
top 0.67% of all time

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1%

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Community
Manager
Community
Manager

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1,784 commits

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1,784 commits
(or roughly, 30%)

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Engines
Engines

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James
Adam
James
Adam

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Oct 31,
2005
Oct 31,
2005

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0.14.2
0.14.2
Rails
Rails

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Kevin
Smith
Kevin
Smith

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“[engines are a]
nasty hack that
breaks every new
version of Rails”
http://glu.ttono.us/articles/2006/08/30/guide-things-you-shouldnt-be-doing-in-rails

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“Stop trying to
write ‘neato ajax
driven thingies’”
http://glu.ttono.us/articles/2006/08/30/guide-things-you-shouldnt-be-doing-in-rails

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“I didn't want Rails to succumb
to the lure of high-level
components like login systems,
forums, content management,
and the likes.” - DHH
http://david.heinemeierhansson.com/arc/000407.html

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“But the goal of Rails is to
create a world where [engines]
are neither needed or strongly
desired. Obviously, we are not
quite there yet.” - DHH
http://weblog.rubyonrails.org/2005/11/11/why-engines-and-
components-are-not-evil-but-distracting

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“Engines have not received the
blessing of the RoR core team,
and I wouldn't expect any
diﬀerent, because it would be
madness to include them in the
core Rails.” - James Adam
http://article.gmane.org/gmane.comp.lang.ruby.rails/29166

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Madness!

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Engine Support
Rails < 2.3
Use engines plugin
https://github.com/lazyatom/engines

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Engine Support
Rails 2.3
LOL
http://railscasts.com/episodes/149-rails-engines

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Yehuda
Katz
Yehuda
Katz

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Piotr
Sarnacki
Piotr
Sarnacki

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Engine Support
Rails 3.0 - Not bad

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Engine Support
Rails 3.1 - OH YEAH

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Before
Spree 1.0

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Spree
Product
App
path/to/engine/app/models/product.rb
Product

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Spree
Product
App
Product
path/to/app/app/models/product.rb
path/to/engine/app/models/product.rb
Product

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~300 lines of
documentation
Rails::Engine

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rails plugin new blorgh

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rails plugin new blorgh --full

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rails plugin new blorgh --full --mountable

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A gem
by default

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gem ‘blorgh’, :git =>
‘git://github.com/radar/blorgh’

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Step away
from the
Gemﬁle

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blorgh.gemspec

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blorgh.gemspec
s.add_development_dependency

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blorgh.gemspec
s.add_development_dependency
s.add_dependency

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lib/blorgh.rb
require ‘blorgh/engine’
module Blorgh
end

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lib/blorgh/engine.rb
module Blorgh
class Engine < Rails::Engine
end
end

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initializer “something” do
# your code here
end
Inside Blorgh::Engine

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config.generators do |g|
g.orm :webscale
end

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Rails::Application <
Rails::Engine

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“In Rails 3.0, a Rails::Application
object was introduced which is
nothing more than an Engine but
with the responsibility of
coordinating the whole boot process.”
Rails::Application

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endpoint SomeRackApp

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Rakeﬁle
(tasks go into lib/tasks)

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conﬁg
initializers
locales
routes

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Generators

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blorgh:install:migrations
Comes standard

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GOOD
README
not included
but for the love of God
write one

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The best Rails 3.1 forum system.

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The best Rails 3.1 forum system.
Ever.

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Namespacing
Namespacing

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rails g model post

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rails g model post
app/models/post.rb

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Forem
Post
App
path/to/engine/app/models/post.rb
Post

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Forem
Post
App
Post
path/to/app/app/models/post.rb
path/to/engine/app/models/post.rb
Post

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“Just call it
something
different”

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Yeah.
Nah.

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isolate_namespace Forem

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rails g model post

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rails g model post
app/models/forem/post.rb

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Forem ::
Post
App
path/to/engine/app/models/forem/post.rb
Post

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Forem ::
Post
App
Post
path/to/app/app/models/post.rb
path/to/engine/app/models/forem/post.rb
Post

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forem_posts

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Forem::PostsController
forem_posts

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Forem::PostsController
app/views/forem/posts
forem_posts

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Rails.application.routes.draw

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Rails.application.routes.draw do
namespace :forem do
resources :forums
end
end
forem/config/routes.rb

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Forem::Engine.routes.draw

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Forem::Engine.routes.draw do
resources :forums
...
end
forem/config/routes.rb

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mount Forem::Engine, :at => “forum”
the_app/config/routes.rb

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forums_path
/forum/forums

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forums_path
forem.
/forum/forums

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dropbears_path
/dropbears

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dropbears_path
main_app.
/dropbears

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form_for [forem, @topic, @post]

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form_for [forem, @topic, @post]
/forums/topics/1/posts

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Hard
Problems

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HOW 2
SHOT
AUTH?

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spree_auth

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http://aubenoire.ﬁles.wordpress.com/2011/05/not-my-problem.jpg

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class ApplicationController
def forem_user
current_user
end
end

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Forem.user_class = “User”
config/initializers/forem.rb
Into
Put

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User#to_s

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Authlogic

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Devise

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Custom

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HOW 2
SHOT AUTH?
(part two)

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CanCan
CanCan

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<% if can?(:read, category) %>

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Forem::DefaultPermissions

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Forem::DefaultPermissions
can_read_forem_forum?(forum)
can_read_forem_category?(category)

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can_read_forem_forum?(forum)
def
true
end

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def can_read_forem_forum?(forum)
# your code goes here
end
app/models/user.rb

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module Forem
class Ability
include CanCan::Ability
def initialize(user)
user ||= Forem.user_class.constantize.new
can :read, Forem::Category do |category|
user.can_read_forem_category?(category)
end
...

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class Forem::ApplicationController
def current_ability
Forem::Ability.new(forem_user)
end
...
end

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<% if can?(:read, category) %>

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Theming

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stylesheet_link_tag “forem/theme/twist”
app/views/layouts/
forem.html.erb

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module Forem
module Theme
module Twist
class Engine < Rails::Engine
end
end
end
end

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Rails::Engine
\m/

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app/assets/stylesheets/
forem/theme/twist.css
forem-theme-twist

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app/assets/stylesheets/
forem/theme/twist.css
forem-theme-twist
javascript + images too!

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Install
+ Setup

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gem ‘forem’,
:git => “git://github.com/radar/forem”

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gem ‘forem’,
bundle install

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gem ‘forem’,
bundle install
rake forem:install:migrations

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gem ‘forem’,
bundle install
rake db:migrate

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gem ‘forem’,
bundle install
rake db:migrate
create config/initializers/forem.rb

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gem ‘forem’,
bundle install
rake db:migrate
Add forem_user method to AppController

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gem ‘forem’,
bundle install
rake db:migrate
Add User#to_s method

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gem ‘forem’,
bundle install
rake db:migrate
Go into console + create first forum

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gem ‘forem’,
bundle install
rake db:migrate
Mount Forem::Engine, :at => ‘/’

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gem ‘forem’,
bundle install
rake db:migrate
Pray that it works.
Mount Forem::Engine, :at => ‘/’

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gem ‘forem’,

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gem ‘forem’,
bundle install

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gem ‘forem’,
bundle install
rails g forem:install

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gem ‘forem’,
bundle install
Answer two questions.

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gem ‘forem’,
bundle install
It works!
Answer two questions.
(assuming you have a User model)

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Spree 1.0

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Namespace
everything

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SpreeCore

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Spree::Core
Spree::Auth

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Spree ::Core::Product

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Spree ::Product

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Spree::
Product
App
Product
path/to/app/app/models/product.rb
path/to/engine/app/models/spree/product.rb
Product

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Forem
Forem

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Forem
App
Forem

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Forem::Engine.routes.draw

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mount Forem::Engine, :at => “forums”

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Core
Auth API
Promo
Dash
Spree

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Core
Auth API
Promo
Dash
App
Spree

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Spree::Core::Engine.routes.draw
Spree::Auth::Engine.routes.draw
Spree::Promo::Engine.routes.draw
Spree::Dash::Engine.routes.draw
Spree::Api::Engine.routes.draw

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mount Spree::Core::Engine, :at => ‘/’
mount Spree::Auth::Engine, :at => ‘/’
mount Spree::Api::Engine, :at => ‘/’
mount Spree::Dash::Engine, :at => ‘/’
mount Spree::Promo::Engine, :at => ‘/’

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mount Spree::Auth::Engine, :at => ‘/’
mount Spree::Api::Engine, :at => ‘/’
mount Spree::Dash::Engine, :at => ‘/’
mount Spree::Promo::Engine, :at => ‘/’
mount Spree::YourExtension, :at => ‘/’

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spree_core.root_path
spree_auth.login_path

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HAHAHAHAHAHAHAHAHAH
AHAHAHAHAHAHAHAHAHA
HAHAHAHAHAHAHAHAHAH
AHAHAHAHAHAHAHAHAHA
HAHAHAHAHAHAHAHAHAH
AHAHAHAHAHAHAHAHAHA
HAHAHAHAHAHAHAHAHAH
AHAHAHAHAHAHAHAHAHA
HAHAHAHAHAHAHAHAHAH
AHAHAHAHAHAHAHAHAHA
HAHAHAHAHAHAHAHAHAH

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spree.login_path
spree.root_path

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Spree::Core::Engine.routes.prepend

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Spree::Core::Engine.routes.prepend do
mount Spree::Auth::Engine, :as => “spree”
end

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Core
Auth API
Promo
Dash
App
Extensions

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Fix
everything

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describe Spree::ProductsController do
it “gets a list of products” do
get :index
end
end
spec/controllers/products_controller_spec.rb

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describe Spree::ProductsController do
it “gets a list of products” do
get :index
end
end
spec/controllers/products_controller_spec.rb
No route matches { :controller =>
“Spree::ProductsController”, :action
=> “index” }

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http://stackoverﬂow.com/a/5832908/15245
How do I write a Rails 3.1
engine controller test in
RSpec?
The workaround is quite simple, instead of this
get :show, :id => 1
use this
get :show, {:id => 1, :use_route => :posts}

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Well,
duh.

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:use_route => :spree

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rails-3.1 (3-1-stable)♐ ack ":use_route"
actionpack/lib/action_dispatch/routing/route_set.rb
actionpack/test/controller/routing_test.rb
actionpack/test/template/form_helper_test.rb

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rails-3.1 (3-1-stable)♐ ack ":use_route"
actionpack/lib/action_dispatch/routing/route_set.rb
actionpack/test/controller/routing_test.rb
actionpack/test/template/form_helper_test.rb
Three ﬁles.
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Rails Engines - Lessons Learned

Rails Engines - Lessons Learned

Ryan Bigg

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