Better view of article on coderwall

ability.rb

class Ability
  include CanCan::Ability
 
  def initialize(user)
 
    user ||= User.new # This is used for not logged user if you have a need for it 
 
    if User.current_role == 'admin' # From ApplicationController we can get current_role and check it up against the role we want.
      can :manage, :all 
    else
      if User.current_role == 'moderator'
        can :read, Products
        can :update, Products
        cannot :destroy, Products
        cannot :create, Products
 
        cannot :manage, Client
      end
 
      can :read, :all
    end
  end
end

application_controller.rb

class ApplicationController < ActionController::Base
 
	before_filter :initialize_company, :initialize_user_role
 
# we find company that user currently uses and we store data in class ( cattr_accessor :current)
 
 
	def initialize_company
		Company.current = Company.find(params[:company_id]) if params.has_key?(:company_id)     
	end
 
# we find user role for companie that he is managing and we store data in class ( cattr_accessor :current_role )
 
	def initialize_user_role
		User.current_role = Unity.where(company_id: Company.current.id, user_id: current_user.id).first.role.name unless Company.current.nil?
	end
end

company.rb

class Company < ActiveRecord::Base
 
  cattr_accessor :current # here I added a current company, so I can check wich company is active I will use that later.
 
  has_many :unities
  has_many :users, through: :unities
  has_many :roles, through: :unities
end

migration file

create_table :unities do |t|
  t.integer :role_id
  t.integer :user_id
  t.integer :company_id
 
 t.timestamps
end

role.rb

class Role < ActiveRecord::Base
 
  has_many :unities
  has_many :users, through: :unities
  has_many :companies, through: :unities
 
end

unity.rb

class Unity < ActiveRecord::Base
 
	attr_accessible :role_id, :user_id, :company_id
	
	belongs_to :role
	belongs_to :company
	belongs_to :user
 
end

user.rb

class User < ActiveRecord::Base
  rolify
 
  cattr_accessor :current_role # I added current_role so I can check which role does user haves on a company that he is on but I will get to that later

  has_many :unities
  has_many :roles, through: :unities
  has_many :companies, through: :unities

end

Question: How did you handle the registration for this example? Did you use the Devise stock sign-up and nest the company / roles in or create the company and then the user / role?