How to integrate CanCan with multiple devise models?

cancan, devise, ruby-on-rails

Solution

Let's assume your app has two separate Devise-powered user models called `User` and `Admin`. This means you use methods like `current_user` and `current_admin` side by side.

Let's further assume that you only have/want a single `Ability` class, which contains all your CanCan permission settings...

class Ability
  include CanCan::Ability

  def initialize(user)
    user ||= User.new
    case user
    when User
      can :create, Comment
      can :read, :all
    when Admin
      can :manage, :all
    end
  end
end

This is exactly what others have proposed, but there's another step you have to take.

By default, CanCan assumes that the method `current_user` exists and will return a User object to compare with your `Ability` settings. However, our admin users can be found using `current_admin`. Without telling CanCan where to find admin objects, they never get reviewed, and thus never get permissions; we must change the defaults when dealing with an admin.

Add the following to `application_controller.rb`...

def current_ability
  if admin_signed_in?
    @current_ability ||= Ability.new(current_admin)
  else
    @current_ability ||= Ability.new(current_user)
  end
end

Now our Ability class will look at the Admin object if one is available, and fall back on a normal User when none is present.

Further development allows us to move Admin permissions into their own separate Ability class...

def current_ability
  if admin_signed_in?
    @current_ability ||= AdminPowers.new(current_admin)
  else
    @current_ability ||= Ability.new(current_user)
  end
end

For more info, see Changing Defaults in the Wiki. Kudos to Stefan for pointing me at the proper article.

FYI -- CanCan is dead, long live CanCanCan! Up to date with bug fixes and new features. Same namespaces, so it's just a drop-in gem replacement in your Gemfile.

gem 'cancancan', '~> 1.8'

Problem

Original source