Sharing common code between Rails controllers with `Scoped` pattern

If you follow a strict REST / nested resources approach to building your Rails app, you might get sick of repeating common controller actions.

Try the Scoped concern pattern: a place to put shared code (setting variables, authorization) and slim down your controllers.

Usage

This particular pattern comes from DHH and Basecamp – a codebase that prides itself of using lots of tiny concerns to share bits of behavior.

While the savings of repeating the same before_actions to look up a Channel would be a fine benefit on it’s own, the naming convention of Scoped is such a great, sharp name. Playlists are “scoped” to a channel so it makes total sense that the corresponding controller would be “channel scoped”.

module ChannelScoped
  extend ActiveSupport::Concern

  included do
    before_action :set_channel, :authorize_channel
  end

  private

  def set_channel
    @channel = Channel.find(params[:channel_id])
  end

  def authorize_channel
    authorize @channel # check that user has access, etc
  end
end

class Channels::SubscriptionsController < ApplicationController
  include ChannelScoped
end

class Channels::VideosController < ApplicationController
  include ChannelScoped
end

class Channels::PlaylistsController < ApplicationController
  include ChannelScoped
end

Additional Resources

DHH Gist: Models for Nested Resources