A#

DRYing up model codes#

Comment Model:

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true
end

Article Model:

class Article < ActiveRecord::Base
  has_many :comments, as: :commentable 

  def find_first_comment
    comments.first(created_at DESC)
  end

  def self.least_commented
   #return the article with least number of comments
  end
end

Event Model

class Event < ActiveRecord::Base
  has_many :comments, as: :commentable 

  def find_first_comment
    comments.first(created_at DESC)
  end

  def self.least_commented
   #returns the event with least number of comments
  end
end

As we can notice, there is a significant piece of code common to both Event and Article. Using concerns we can extract this common code in a separate module Commentable.

For this create a commentable.rb file in app/models/concerns.

module Commentable
  extend ActiveSupport::Concern

  included do
    has_many :comments, as: :commentable
  end

  # for the given article/event returns the first comment
  def find_first_comment
    comments.first(created_at DESC)
  end

  module ClassMethods
    def least_commented
      #returns the article/event which has the least number of comments
    end
  end
end

And now your models look like this :

Comment Model:

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true
end

Article Model:

class Article < ActiveRecord::Base
  include Commentable
end

Event Model:

class Event < ActiveRecord::Base
  include Commentable
end

Skin-nizing Fat Models.#

Consider a Event model. A event has many attenders and comments.

Typically, the event model might look like this

class Event < ActiveRecord::Base   
  has_many :comments
  has_many :attenders


  def find_first_comment
    # for the given article/event returns the first comment
  end

  def find_comments_with_word(word)
    # for the given event returns an array of comments which contain the given word
  end 

  def self.least_commented
    # finds the event which has the least number of comments
  end

  def self.most_attended
    # returns the event with most number of attendes
  end

  def has_attendee(attendee_id)
    # returns true if the event has the mentioned attendee
  end
end

Models with many associations and otherwise have tendency to accumulate more and more code and become unmanageable. Concerns provide a way to skin-nize fat modules making them more modularized and easy to understand.

The above model can be refactored using concerns as below: Create a attendable.rb and commentable.rb file in app/models/concerns/event folder

attendable.rb

module Attendable
  extend ActiveSupport::Concern

  included do 
    has_many :attenders
  end

  def has_attender(attender_id)
    # returns true if the event has the mentioned attendee
  end

  module ClassMethods
    def most_attended
      # returns the event with most number of attendes
    end
  end
end

commentable.rb

module Commentable
  extend ActiveSupport::Concern

  included do 
    has_many :comments
  end

  def find_first_comment
    # for the given article/event returns the first comment
  end

  def find_comments_with_word(word)
    # for the given event returns an array of comments which contain the given word
  end

  module ClassMethods
    def least_commented
      # finds the event which has the least number of comments
    end
  end
end

And now using Concerns, your Event model reduces to

class Event < ActiveRecord::Base
  include Commentable
  include Attendable
end

This post helped me understand concerns.

app/models/trader.rb#

class Trader
  include Shared::Schedule
end

app/models/concerns/shared/schedule.rb#

module Shared::Schedule
  extend ActiveSupport::Concern
  ...
end

JJJ#

app/models/trader.rb#

class Trader
  include Shared::Schedule
end

app/models/concerns/shared/schedule.rb#

module Shared::Schedule
  extend ActiveSupport::Concern
  ...
end

module M
  def self.included(base)
    base.extend ClassMethods
    base.class_eval do
      scope :disabled, -> { where(disabled: true) }
    end
  end

  def instance_method
    ...
  end

  module ClassMethods
    ...
  end
end

After refactoring with ActiveSupport::Concern.

require 'active_support/concern'

module M
  extend ActiveSupport::Concern

  included do
    scope :disabled, -> { where(disabled: true) }
  end

  class_methods do
    ...
  end

  def instance_method
    ...
  end
end

Example 2: Handle module dependencies gracefully.

module Foo
  def self.included(base)
    base.class_eval do
      def self.method_injected_by_foo_to_host_klass
        ...
      end
    end
  end
end

module Bar
  def self.included(base)
    base.method_injected_by_foo_to_host_klass
  end
end

class Host
  include Foo # We need to include this dependency for Bar
  include Bar # Bar is the module that Host really needs
end

After refactoring with ActiveSupport::Concern

require 'active_support/concern'

module Foo
  extend ActiveSupport::Concern
  included do
    def self.method_injected_by_foo_to_host_klass
      ...
    end
  end
end

module Bar
  extend ActiveSupport::Concern
  include Foo

  included do
    self.method_injected_by_foo_to_host_klass
  end
end

class Host
  include Bar # It works, now Bar takes care of its dependencies
end

For example I want in my application where attribute create_by exist update there value by 1, and 0 for updated_by

module TestConcern 
  extend ActiveSupport::Concern

  def checkattributes   
    if self.has_attribute?(:created_by)
      self.update_attributes(created_by: 1)
    end
    if self.has_attribute?(:updated_by)
      self.update_attributes(updated_by: 0)****
    end
  end

end

If you want to pass arguments in action

included do
   before_action only: [:create] do
     blaablaa(options)
   end
end

after that include in your model like this:

class Role < ActiveRecord::Base
  include TestConcern
end

MOre sample#

as#

class Comment < ActiveRecord::Base
  attr_accessible :body, :email, :name, :article_id

  belongs_to :article

  validates :name, :email, :body, :presence => true
  validates :article_should_be_published

  def article_should_be_published
    errors.add(:article_id, "is not published yet") if article && !article.published?
  end
end

class Article < ActiveRecord::Base
  attr_accessible :body, :published_at, :title

  validates :title, :presence => true
  validates :body, :presence => true

  belongs_to :user
  has_and_belongs_to_many :categories
  has_many :comments

  scope :published, where("articles.published_at IS NOT NULL")
  scope :draft, where("articles.published_at IS NULL")
  # recent post from < a month ago - see pg 103 of tutorial
  # scope :recent, lambda { published.where("articles.published_at > ?", 1.month.ago.to_date)}
  scope :where_title, lambda { |term| where("articles.title LIKE ?", "%#{term}%") }

  def long_title
    "#{title} - #{published_at}"
  end

  def published?
    published_at.present?
  end
end