Create base controller

To keep codes clear, we usually put controllers with same business scope into the same directory. In most cases, these controllers will share some functions, so we can create a base controller for them for DRY.

For example, we have a list of controllers for content management:

admin
  content
    articles_controller
    comments_controller
    scores_controller
  other
    others_controller

Normally, controllers under admin directory should require current_user to be an admin, so we need to add before_filter :admin_required for each controller. Where's the best place to do this? The "base" controller for admin.

The file structure after adding base controllers:

admin
  content
     articles_controller.rb
     comments_controller.rb
     scores_controller.rb
     base_controller.rb
  other
     others_controller.rb
  base_controller.rb

Example codes for admin/base_controller

class Admin::BaseController < ApplicationController
  before_filter :admin_required
  protected
  def admin_required
    # implementation
  end
end

Example codes for admin/content/base_controller

class Admin::Content::BaseController < Admin::BaseController
  before_filter :find_article
  protected
  def find_article
    @article = Article.find_by_id(params[:id])
  end
end

For controllers under admin/content, they just need to inherit from admin/content/base_controller.

Some examples that can (and should) be put in base controllers:

1. Access controll
2. layout selector
3. Initialize variables that will be used in most actions. (like @article in the above example)