Persisting guests users in devise.

application_controller.rb

# use this if you are using cancan/cancancan gem for authoriazation. This passes your new current_or_guest_user method to cancan rather
# than the usual devise current_user method

def current_ability
  @current_ability ||= Ability.new(current_or_guest_user)
end

Authorization_helper.rb

module AuthorizationHelper

  # if user is logged in, return current_user, else return guest_user
  def current_or_guest_user
    if current_user
      if cookies.signed[:guest_user_id]
        logging_in
        guest_user.delete
        cookies.delete :guest_user_id
      end
      current_user
    else
      guest_user
    end
  end

  # find guest_user object associated with the current session,
  # creating one as needed
  def guest_user
    # Cache the value the first time it's gotten.
    @cached_guest_user ||=
      User.find_by!(id: (cookies.permanent.signed[:guest_user_id] ||= create_guest_user.id))

  # if cookies.signed[:guest_user_email] invalid
  rescue ActiveRecord::RecordNotFound #
    cookies.delete :guest_user_id
    guest_user
  end

  private

  # called (once) when the user logs in, insert any code your application needs
  # to hand off from guest_user to current_user.
  def logging_in
    # For example:
    # guest_bookings = guest_user.bookings.all
    # guest_bookings.each do |booking|
      # booking.user_id = current_user.id
      # booking.save!
    # end
  end

  # creates guest user by adding a record to the DB
  # with a guest name and email
  def create_guest_user
    # pass client into the user job
    c = Client.new(:firstname => "guest")
    c.build_user(:email => "guest_#{Time.now.to_i}#{rand(99)}@example.com")
    c.save!(:validate => false)
    c
  end

end