bookstore/app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
  helper_method :current_user
  helper_method :logged_in?

  def current_user
    User.find_by(id: session[:user_id])
  end
  
  def logged_in?
    !current_user.nil?
  end

  def notices_from_errors(record)
    messages = record.errors.messages.map do |attribute, messages|
      messages.map { |message| "#{attribute} #{message}".capitalize }
    end
    messages.flatten
  end
end