Create a guest user in Rails

rails_guest_user_example.rb

# [1]
class AddGuestToUsers < ActiveRecord::Migration[6.0]
  def change
    add_column :users, :guest, :boolean, default: false, null: false
  end
end

# [2]
module GuestUser
  extend ActiveSupport::Concern

  private
    
    # [2.1]
    def create_guest_user
      # [2.1.1]
      user = User.new(email: "#{SecureRandom.uuid}@#{SecureRandom.uuid}.com", guest: true)
      # [2.1.2]
      user.save!(validate: false)
      # [2.1.3]    
      session[:guest_user_id] = user.id
      # [2.1.4]
      user
    end
    
    # [2.1]
    def destroy_guest_user_session
      session[:guest_user_id] = nil
    end  
     
    # [2.3]
    def set_guest_user
      # [2.3.1]
      User.find_by(id: session[:guest_user_id]).present? ? User.find_by(id: session[:guest_user_id]) : create_guest_user
    end
end

# [3]
class PostsController < ApplicationController
  # [3.1]
  include GuestUser
  # [3.2]
  before_action :set_guest_user, only: :create
end

# [4]
class Users::SessionsController < Devise::SessionsController
  # [4.1]
  include GuestUser
   
  # [4.2]
  def create
    super
    destroy_guest_user_session
  end

end

########
# Notes
########

# [1]: Add a `guest` column to your `users` table. This will allow you to identify user records created as guests. Useful for running a script to delete old records.
# [2]: Create a Concern to hold shared logic between Controllers.
# [2.1]: Add a private method that create a guest user.
# [2.1.1]: Use `SecureRandom.uuid` to ensure the email is unique, and set `guest` to `true`.
# [2.1.2]: Save the record without having it validated. This is necessary to avoid setting a password. 
# [2.1.3]: Create a new session key set to the id of the user created. This is necessary for looking up the guest user.
# [2.1.4]: Make sure to return the user from this method.
# [2.2]: Add a private method that queries for the guest user.
# [2.3]: TODO
# [2.3.1]: TOD:
# [3.1]: Include the Concern in any Controller where you need a guest user.
# [3.2]: Query for the guest user on specific controller actions.
# [4.1]: TODO
# [4.2]: TODO

##########
# Gotchas
##########

# This specific apprach only works if you're not requiring user authentication on a particular controller#action. You'll notice in step 3 there's not before_action :authenticate_user!