What is ||= in rails?

Question

class ApplicationController < ActionController::Base

  private

  # Finds the User with the ID stored in the session with the key
  # :current_user_id This is a common way to handle user login in
  # a Rails application; logging in sets the session value and
  # logging out removes it.
  def current_user
    @_current_user ||= session[:current_user_id] &&
      User.find_by_id(session[:current_user_id])
  end
end

How to understand the code above? What does ||= mean? And is @_current_user an id or a user object? Also, why it starts with _?

Can anyone answer me what @_current_user is?

That post's answer is not good. And it does not answer my other questions about `@_current_user`. — OneZero, Mar 31 '13 at 00:18
http://stackoverflow.com/questions/8506257/operator-in-ruby - search for "ruby operators". — , Mar 31 '13 at 00:22

score 1 · Answer 1 · edited May 23 '17 at 11:49

1

Per this question, a ||= b is shorthand for a || a = b.

And regarding the value of @_current_user, if we assume session[:current_user_id] is 5, then the && operator with the User model will return the User instance:

> 5 && User.new(:name => 'Foo')
=> #<User name="Foo">

So @_current_user will be the User instance.

edited May 23 '17 at 11:49

Community

1
1

answered Mar 31 '13 at 00:24

Stuart M

11,458
6
45
59

in simply says, it just fetches data from the database to avoid hitting the database again and again for each request, we just decide if @_currentuser already fetched just return, if not go and just fetch and return. – Mooventhan Sep 18 '21 at 16:09

What is ||= in rails?

1 Answers1