Michael Hartl chapter 8.3 logging out sessions - ruby-on-rails

Question

I'm going through Michael Hartl's The Ruby on Rails Tutorial, Chapter 8.3 Logging Out Sessions and I don't understand how removing the session[:user_id] can remove the #current_user as well:
here is the SessionController:
class SessionsController < ApplicationController
def new
end
def create
user =User.find_by(email: params[:session][:email].downcase)
if user && user.authenticate(params[:session][:password])
log_in(user)
redirect_to user
else
#flash.now will only flash once - if a new request or view is rendered,the flash will go away now
flash.now[:danger] = 'Invalid email/password combination'
render 'new'
end
end
def destroy
log_out
redirect_to root_path
end
end
and here is the SessionsHelper for the login and logout helpers:
module SessionsHelper
def log_in(user)
session[:user_id] = user.id
end
def current_user
#find the user if #user is not defined yet, or else, just keep the current user
#that way we dont have to do a database search every time current_user is called
#current_user ||= User.find_by(id: session[:user_id])
end
def logged_in?
!current_user.nil?
end
def log_out
session.delete(:user_id)
end
end
The way I understand, once #current_user is defined once logged in, shouldn't the variable still last even though the session[:user_id] has been removed since it is being set to itself?
#current_user ||= User.find_by(id: session[:user_id])
There was no action that I am aware of that removed the #current_user variable. But when I tested it during the debugger, I can see that once someone logs out, #current_user becomes nil.
Can someone explain the mechanics to me?

Answer 1

The session persists between requests. But the instance variable #current_user only persists for the length of one request. When the destroy action redirects to the root_path that is the start of a new request which will load the root page.
You may want to try this out so see that clearing the user_id out of the session doesn't clear out the instance variable:
def destroy
# Test code to initialize #current_user
current_user
Rails.logger.debug("#current_user before: #{#current_user.inspect}")
log_out
# Test code to check #current_user after updating session
Rails.logger.debug("#current_user after: #{#current_user.inspect}")
redirect_to root_path
end
And then check what ends up in log/development.log. #current_user will still be present after log_out but it will go away at the end of the request.