if user logged_in? チュートリアル

Chapter 8: Log in, log out | Ruby on Rails Tutorial (3rd Ed.) | Softcover.io

Listing 8.15: The logged_in? helper method.app/helpers/sessions_helper.rb

module SessionsHelper

  # Logs in the given user.
  def log_in(user)
    session[:user_id] = user.id
  end

  # Returns the current logged-in user (if any).
  def current_user
    @current_user ||= User.find_by(id: session[:user_id])
  end

  # Returns true if the user is logged in, false otherwise.
  def logged_in?
    !current_user.nil?
  end
end