Setting up UUID columns for Rails 5+ models utilizing Postgres 9.4+

1_initial_migration.rb

class InitialMigration < ActiveRecord::Migration[5.0]
  def change
    enable_extension "pgcrypto" unless extension_enabled?("pgcrypto")
  end
end

2_example_migration.rb

class ExampleMigration < ActiveRecord::Migration[5.0]
  create_table :comments, id: :uuid, default: 'gen_random_uuid()' do |t|
    # t.belongs_to :post, type: :uuid
    t.references :post, type: :uuid
  end
end

README.md

Notes

• Default sorting in Rails is on the id column, which is no longer relevant when uuid types are used.
• A default scope of default_scope -> { order("created_at ASC") } may be necessary for models.
• Also a consideration is adding an index for the created_at column:

class AddCreatedAtIndexes < ActiveRecord::Migration
  def up
    add_index :categories, :created_at
    add_index :products, :created_at
    add_index :users, :created_at
  end
end

Refs

• (official) http://guides.rubyonrails.org/active_record_postgresql.html#uuid-primary-keys
• (example) http://blog.bigbinary.com/2016/04/04/rails-5-provides-application-config-to-use-UUID-as-primary-key.html
• (for default uuid) rails/rails#22033
• (example) https://www.penflip.com/loren/blog/blob/master/migrating-to-uuids.txt

application.rb

# This change should allow model generators to include instructions for uuid types by default

require_relative "boot"

...

module AppName
  class Application < Rails::Application
    # Settings in config/environments/* take precedence over those specified here.
    # Application configuration should go into files in config/initializers
    # -- all .rb files in that directory are automatically loaded.
    config.generators do |generator|
      generator.orm :active_record, primary_key_type: :uuid
    end
  end
end