Rails4 Use concern namespaces

1 Set up your rails 4 app to load subfolders of /app/models/concerns

# /config/application.rb
class Application < Rails::Application
  config.autoload_paths += Dir["#{Rails.root}/app/models/concerns/**/*.rb"]
end

2 Set up subfolders.

Say you have a User model and you want to refacture validations into a module for it.

mkdir /app/models/concerns/user
touch /app/models/concerns/user/validations.rb

3 Require this module in User model definition

# /app/models/user.rb

require_dependency 'user/validations' # this may be necessary if dependency breakage occurs
class User < ActiveRecord::Base
  include User::Validations
end

4 Populate the module with code

# in /app/models/concerns/user/validations.rb

class User < ActiveRecord::Base
  module Validations
    extend ActiveSupport::Concern

    included do
      validates :email, uniqueness: {message: "Email already taken!"}, presence: {message: "Email must be present!"}
      scope :expires_on, ->(date) { where(expiration_date: date.to_date.beginning_of_day..date.to_date.end_of_day) }
    end

    module ClassMethods
      def some_class_method
        # code
      end
    end

    def some_instance_method
      # code
    end
  end
end

It is OK to have a User model definition looking like:

class User < ActiveRecord::Base
  include User::Validations
  include User::Decorators
  include User::ClassMethods
  include User::ThatCoreBusinessLogic
  include User::Messaging

  scope :adults, -> { where(age: 18..999) }
  scope :children, -> { where(age: 0..17) }

end

Written on May 10, 2015