ActiveRecord Playground File `irb -r ./playground.rb` (or `pry ...`)

playground.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'
  gem 'sqlite3'
  gem 'activerecord', "~> 6.0.0.rc2"
end

require 'active_record'

ActiveRecord::Base.belongs_to_required_by_default = true
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')

ActiveRecord::Schema.define do
  create_table :posts, force: true do |t|
    t.string :title
    t.text :content

    t.timestamps
  end

  create_table :comments, force: true do |t|
    t.string :name
    t.text :content
    t.belongs_to :post, index: true

    t.timestamps
  end
end

class Post < ActiveRecord::Base
  has_many :comments, dependent: :destroy
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

post = Post.create(title: 'Hello World!', content: "Look at all the things I'm not doing.")

3.times do |comment|
  post.comments.create(name: "User #{comment}", content: "I wrote comment ##{comment}")
end

=begin
  [1] pry(main)> Post.count
  => 1

  [2] pry(main)> Post.first.comments
  => [#<Comment:0x00007fec2e379980 id: 1, name: "User 0", content: "I wrote comment #0", post_id: 1, created_at: 2019-01-04 14:28:23 UTC, updated_at: 2019-01-04 14:28:23 UTC>,
      #<Comment:0x00007fec2e3795e8 id: 2, name: "User 1", content: "I wrote comment #1", post_id: 1, created_at: 2019-01-04 14:28:23 UTC, updated_at: 2019-01-04 14:28:23 UTC>,
      #<Comment:0x00007fec2e3792c8 id: 3, name: "User 2", content: "I wrote comment #2", post_id: 1, created_at: 2019-01-04 14:28:23 UTC, updated_at: 2019-01-04 14:28:23 UTC>]
=end