Concern version of https://gist.github.com/uberllama/7505705

gistfile1.rb

# app/models/comment.rb
class Comment < ActiveRecord::Base
  include TrackableObserver

  belongs_to :user
  has_many :activities, as: :trackable
end
 
# app/models/like.rb
class Like < ActiveRecord::Base
  include TrackableObserver

  belongs_to :user
  has_many :activities, as: :trackable
end
 
# app/models/activity.rb
class Activity < ActiveRecord::Base
  belongs_to :user
  belongs_to :trackable, polymorphic: true
end
 
# /app/models/concerns/trackable_observer.rb
module TrackableObserver
  extend ActiveSupport::Concern
  
  included do
    after_create :create_activity
  end
  
  private
  
  def create_activity
    activities.create(user_id: user_id)
  end
  
end