How to get Devise's current_user in ActiveRecord callback in Rails?

Question

I'm using Devise and Rails 3.2.16. I want to automatically insert who created a record and who updated a record. So I have something like this in models:

before_create :insert_created_by
before_update :insert_updated_by

private
def insert_created_by
  self.created_by_id = current_user.id
end
def insert_updated_by
  self.updated_by_id = current_user.id
end

Problem is that I get the error undefined local variable or method 'current_user' because current_user is not visible in a callback. How can I automatically insert who created and updated this record?

If there's an easy way to do it in Rails 4.x I'll make the migration.

Answer 1

Editing @HarsHarl's answer would probably have made more sense since this answer is very much similar.

With the Thread.current[:current_user] approach, you would have to make this call to set the User for every request. You've said that you don't like the idea of setting a variable for every single request that is only used so seldom; you could chose to use skip_before_filter to skip setting the User or instead of placing the before_filter in the ApplicationController set it in the controllers where you need the current_user.

A modular approach would be to move the setting of created_by_id and updated_by_id to a concern and include it in models you need to use.

Auditable module:

# app/models/concerns/auditable.rb

module Auditable
  extend ActiveSupport::Concern

  included do 
    # Assigns created_by_id and updated_by_id upon included Class initialization
    after_initialize :add_created_by_and_updated_by

    # Updates updated_by_id for the current instance
    after_save :update_updated_by
  end

  private

  def add_created_by_and_updated_by
    self.created_by_id ||= User.current.id if User.current
    self.updated_by_id ||= User.current.id if User.current
  end

  # Updates current instance's updated_by_id if current_user is not nil and is not destroyed.
  def update_updated_by
    self.updated_by_id = User.current.id if User.current and not destroyed?
  end
end

User Model:

#app/models/user.rb
class User < ActiveRecord::Base
  ...

  def self.current=(user)
    Thread.current[:current_user] = user
  end

  def self.current
    Thread.current[:current_user]
  end
  ...
end

Application Controller:

#app/controllers/application_controller

class ApplicationController < ActionController::Base
  ...
  before_filter :authenticate_user!, :set_current_user

  private

  def set_current_user
    User.current = current_user
  end
end

Example Usage: Include auditable module in one of the models:

# app/models/foo.rb
class Foo < ActiveRecord::Base
  include Auditable
  ...
end

Including Auditable concern in Foo model will assign created_by_id and updated_by_id to Foo's instance upon initialization so you have these attributes to use right after initialization, and they are persisted into the foos table on an after_save callback.