Very simple permissions that I have used on my last several projects so I figured it was time to abstract and wrap up into something more easily reusable.
Whatever class you want all permissions to run through should include Cannabis::Cans.
class User include MongoMapper::Document include Cannabis::Cans end
This means that an instance of a user automatically gets can method for the default REST actions: can?(:view, resource), can?(:create, resource), can?(:update, resource), can?(:destroy, resource).
Each of the can methods simply calls the related “able” method (viewable, creatable, updatable, destroyable) for the action (view, create, update, delete). Cannabis comes with defaults for this methods that you can then override as makes sense for your permissions.
class Article include MongoMapper::Document include Cannabis::Ables end
Including Cannabis::Ables adds the able methods to the class including it. In this instance, article now has viewable_by?(user), creatable_by?(user), updatable_by?(user) and destroyable_by?(user).
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 Cannabis::Ables userstamps! # adds creator and updater def updatable_by?(user) creator == user end def destroyable_by?(user) updatable_by?(user) end end
Lets look at some sample code now:
john = User.create(:name => 'John') steve = User.create(:name =. 'Steve') ruby = Article.new(:title => 'Ruby') john.can?(:create, ruby) # true steve.can?(:create, ruby) # true ruby.creator = john ruby.save 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 Cannabis::Enforcers end
Including Cannabis::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 Cannabis action:
class ApplicationController include Cannabis::Enforcers delegate :can?, :to => :current_user helper_method :can? # so you can use it in your views hide_action :can? private def authorize!(action, resource) raise Cannabis::Exceptions::Transgression unless can?(action, resource) end end
Which means you can use it like this:
class ArticlesController < ApplicationController def show @article = Article.find!(params[:id]) authorize!(:view, @article) end end
If the user can? :view the article, all is well. If not, a Cannabis::Exceptions::Transgression is raised which you can decide how to handle (show 404, slap them on the wrist, etc.).
You can add your own actions like this:
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.
Copyright © 2010 John Nunemaker. See LICENSE for details.