Rails::Decorators
Using Rails engines extensively, we needed a way to customize behavior for implementations of the platform. Rails provides a great mechanism for views and assets, but doesn't offer any functionality to handle controller/model/lib overriding/customizing. The suggested mechanism in the documentation is class_eval
or ActiveSupport::Concern. Our preferred method for this is module prepending, which is cleaner than class_eval
in that it avoids alias method chaining and becomes part of the ancestor chain.
We also want junior developers to be able to jump in and be productive ASAP - not necessarily requiring they learn the techniques of class_eval
to fix a bug or get a simple task done. Yes, we educate and promote this as the developer grows, but we want the barriers to contribution as low as possible.
We like the ActiveSupport::Concern
API, so this library mimics the API of ActiveSupport::Concern
and layers on top some niceties for the specific task of customizing a Rails engine. Also, we don't like having to store decorated behavior in a separate directory (like https://github.com/parndt/decorators). Storing decorations in the same place as new classes makes it much easier to see the overall picture of how the engine has been customized/extended in one shot.
Usage
Say we have a class in an engine like so:
# in ecommerce/app/models/ecommerce/product.rb
module Ecommerce
class Product < ApplicationRecord
def price
skus.first.price
end
end
end
Rails::Decorators
allows customizing this class like so:
# in Rails.root/app/models/ecommerce/product.decorator
module Ecommerce
decorate Product do
decorated do
# Class methods may be called here. Evaluates after prepending module.
attr_writer :on_sale
end
class_methods do
# Methods defined here extend/decorate static methods on the
# decorated class.
def sorts
super + ['discount_rate']
end
end
# Methods defined here extend/decorate instance methods on the
# decorated class.
def price
result = super
result *= discount_rate if on_sale?
result
end
end
end
Rails::Decorators
achieves this in a manner similar to ActiveSupport::Concern
- it dynamically creates a module out of the block passed, and then prepends that into the original class. The above is equivalent to (note that this would need to be required as well):
# in Rails.root/app/models/ecommerce/product_decorator.rb
module Ecommerce
class Product
module Decorator
module ClassMethods
# Methods defined here extend/decorate static methods on the
# decorated class.
def sorts
super + ['discount_rate']
end
end
# Methods defined here extend/decorate instance methods on the
# decorated class.
def price
result = super
result *= discount_rate if on_sale?
result
end
end
end
Product.send(:prepend, Product::Decorator)
Product.singleton_class.send(:prepend, Product::Decorator::ClassMethods)
Product.class_eval do
# Class methods may be called here. Evaluates after prepending module.
attr_writer :on_sale
end
end
You can also decorate more than one class at a time:
# in Rails.root/app/models/ecommerce/navigable.decorator
module Ecommerce
decorate Product, Category, Page do
def generate_slug
# my custom logic here
end
end
end
Other engines may want to namespace their customizations so as not to collide with further customizations:
# in ecommerce_blog/app/models/ecommerce/product.decorator
module Ecommerce
decorate Product, with: 'blog' do
def blog_entries
BlogEntry.for_product(id)
end
end
end
It is strongly suggested you update your editor of choice to use Ruby syntax highlighting on *.decorator files.
Case Study: Modifying Devise
Let's examine a more real-world case: In the Devise OmniAuth How-To
Article,
the maintainers instruct users to create a new controller named
Users::OmniauthCallbacksController
that inherits from
Devise::OmniauthCallbacksController
, and override the entire class in
the devise_for
method by supplying the name of the controller to use.
This has always been a point of contention for some as it's quite
difficult to understand why you need to do this if you don't have a lot
of experience with Rails applications.
However, if you had rails-decorators
installed, you don't need to do
any of that. Just decorate the controller supplied by Devise in
app/controllers/devise/omniauth_callbacks_controller.decorator!
module Devise
decorate OmniauthCallbacksController do
# We're using Facebook as an example here so it can be directly
# translated from the aforementioned article...
def facebook
# You need to implement the method below in your model (e.g. app/models/user.rb)
@user = User.from_omniauth(request.env["omniauth.auth"])
if @user.persisted?
sign_in_and_redirect @user, event: :authentication #this will throw if @user is not activated
set_flash_message(:notice, :success, kind: "Facebook") if is_navigational_format?
else
session["devise.facebook_data"] = request.env["omniauth.auth"]
redirect_to new_user_registration_url
end
end
def failure
redirect_to root_path
end
end
end
With rails-decorators
, you get to skip about 3 or 4 paragraphs of docs
and go right to the .from_omniauth
definition. Decorating saves both
time and mental energy so you can get back to actually writing your
application.
Installation
Add this line to your application's Gemfile:
gem 'rails-decorators'
And then execute:
$ bundle
Or install it yourself as:
$ gem install rails-decorators
Contributing
Contribution directions go here.
License
The gem is available as open source under the terms of the MIT License.