Super Simple Active Record Example

gistfile1.rb

require 'active_record'
require 'sqlite3'

ActiveRecord::Base.establish_connection( adapter: 'sqlite3', database: ":memory:" )

ActiveRecord::Schema.define(version: 1) do
  create_table :articles do |t|
    t.string  :title
    t.date    :published_at
    t.timestamps
  end

  create_table :comments do |t|
    t.string  :content
    t.integer :article_id
    t.date    :published_at
    t.timestamps
  end
end

class Article < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :article
end

module Commentable
  extend ActiveSupport::Concern

  included do |base|
    has_many :comments, as: :commentable
  end
end

Article.delete_all
Comment.delete_all

@article = Article.create(
  title: 'My article',
  published_at: Date.today
)

Comment.create(
  content: 'I liked your article',
  published_at: Date.today,
  article_id: @article.id)

Comment.create(
  content: 'Ditto',
  published_at: Date.today,
  article_id: @article.id
)