Fully explain session

Another version for session

## This is saying the same thing

  def current_user
    if session[:user_id]
      @current_user ||= User.find(session[:user_id])
    end
  end

  helper_method :current_user
end

Explanation of Session

Learning:
You are using a method called current_user. If there is a user_id in the session hash and current_user is nil then with the user id we have in the session and we know we have a :user_id then go find the user from the database and assign that user and all its properties to @current_user. 

This then allows us to do case.user_id or current_user.id or case.name

class ApplicationController < ActionController::Base
  protect_from_forgery


private

  def current_user
    if session[:user_id]
      if @current_user.nil?
        @current_user = User.find(session[:user_id])
      end
    end

    return @current_user
  end