Simple role based permissions for Ruby projects featuring Actors, Cans, Ables, and Roles.
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Canable (by John Nunemaker) with a Role Based Access System latched on

Simple permissions system that features easily actors, resources for actors to manipulate, and roles actors play to define their permissions.


Ables are the resource objets that an actor will want to manipulate.

class Article
  include MongoMapper::Document
  include Canable::Ables

Including Canable::Ables adds the able methods to the class including it. In this instance, any article instance now has viewable_by?(actor), creatable_by?(actor), updatable_by?(actor) and destroyable_by?(actor).


The rules that govern your actors are defined in roles. Roles are modules that extend Canable::Role and/or other roles. Roles can be nested as deep and mixed and matched using Ruby's mixin system, as they are just normal Ruby modules that carry permission sets with them. The order they are included in each other will define the final permission set of the role: Roles included after (on a lower line) than others will override the settings of the others. module Canable::Roles

	  module EmployeeRole
	    include Canable::Role
	    default_response false

def can_view_article?(article) true end

def can_update_article?(article) article.owner == @name end

def can_destroy_article?(article) self.can_update_article?(article) end end

module ManagerRole include Canable::Role include EmployeeRole

def can_update_article?(article) true end

def can_destroy_article(article) article.owner == @name end end end

Here two roles are defined, one for employees and one for managers. Employees by default can't do anything, this is set by default_response false on the module. Then methods governing the actor's interaction with the Article model by defining the can_view_article? to always return true (Employees can view any article), and defining the can_update_article? method to only return true if the actor playing the employee role is the owner of the article.

The manager role includes the employee role, so it inherits the default_response behaviour of false and the defined rules for interactions with articles. Here, the can_update_article? method is override to always return true, so managers can edit any article. Note that EmployeeRole#can_destroy_article?(article) calls self.can_update_article?(article), so when the ManagerRole inherits the EmployeeRole, ManagerRole#can_destroy_article?(article) returns the result of ManagerRole#can_update_article?(article), which returns true. This means that when ManagerRole inherits EmployeeRole, the inherited methods behave differently, which might be unexpected. To mitigate this in the example above, ManagerRole#can_destroy_article?(article) is overridden to check if the Manager trying to destroy the role is the article owner.


Whatever class(es) you want all permissions to run through should include Canable::Actor, instead of Canable::Cans from the original Canable gem.

class User > ActiveRecord::Base
  include Canable::Actor

default_role :employee


Actors represent objects in the system that want to preform an action. An actor's abilities are defined by the role(s) it plays because the actor simply inherits any permission. Roles can be assigned to an actor (“played”) by using the default_role(role) class method, or calling <tt>act(role)<tt> on an actor instance.

Lets say an article can be viewed and created by anyone, but only updated or destroyed by the user that created the article. To do that, you could leave viewable_by? and creatable_by? alone as they default to true and just override the other methods.

class Article
  include MongoMapper::Document
  include Canable::Ables
  userstamps! # adds creator and updater

  def updatable_by?(user)
    creator == user

  def destroyable_by?(user)

Lets look at some sample code now:

john = User.create(:name => 'John')
steve = User.create(:name =. 'Steve')

ruby = => 'Ruby')
john.can_create?(ruby) # true
steve.can_create?(ruby) # true

ruby.creator = john

john.can_view?(ruby) # true
steve.can_view?(ruby) # true

john.can_update?(ruby) # true
steve.can_update?(ruby) # false

john.can_destroy?(ruby) # true
steve.can_destroy?(ruby) # false

Now we can implement our permissions for each resource and then always check whether a user can or cannot do something. This makes it all really easy to test. Next, how would you use this in the controller.


class ApplicationController
  include Canable::Enforcers

Including Canable::Enforcers adds an enforce permission method for each of the actions defined (by default view/create/update/destroy). It is the same thing as doing this for each Canable action:

class ApplicationController
  include Canable::Enforcers

  delegate :can_view?, :to => :current_user
  helper_method :can_view? # so you can use it in your views
  hide_action :can_view?

    def enforce_view_permission(resource)
      raise Canable::Transgression unless can_view?(resource)

Which means you can use it like this:

class ArticlesController < ApplicationController
  def show
    @article = Article.find!(params[:id])

If the user can_view? the article, all is well. If not, a Canable::Transgression is raised which you can decide how to handle (show 404, slap them on the wrist, etc.).

Adding Your Own Actions

You can add your own actions like this:

Canable.add(:publish, :publishable)

The first parameter is the can method (ie: can_publish?) and the second is the able method (ie: publishable_by?).


So, lets review: cans go on user model, ables go on everything, you override ables in each model where you want to enforce permissions, and enforcers go after each time you find or initialize an object in a controller. Bing, bang, boom.

Note on Patches/Pull Requests

  • Fork the project.

  • Make your feature addition or bug fix.

  • Add tests for it. This is important so I don't break it in a future version unintentionally.

  • Commit, do not mess with rakefile, version, or history. (if you want to have your own version, that is fine but bump version in a commit by itself I can ignore when I pull)

  • Send me a pull request. Bonus points for topic branches.


Copyright © 2010 John Nunemaker. See LICENSE for details.