Developing a web application with multiple user types can lead to tons of
headaches about authorization. Trying to come up with my own solution led to
lots of logic in
before_actions in controllers, and even more awkward logic
in views shared by multiple user types that required slight differences. This
mess also extended throughout multiple files, making it even worse.
Fed up, I found a gem called CanCanCan that made authorization so much simpler. Rather than lots of checks spread throughout your codebase, CanCanCan keeps it all together with an intuitive DSL.
I’ve set up a typical example below. I’d normally explain a code segment before, but I think CanCanCan’s DSL is so easy to read that it does not require anything but the few comments.
# app/models/ability.rb class Ability include CanCan::Ability def initialize(user) alias_action :create, :read, :update, :destroy, to: :crud if user.is_admin? or user.is_moderator? # Admins and mods can CRUD any post can :crud, Post else # Normal users can CRUD their own post can :crud, Post, user_id: user.id # But they can only read others can :read, Post end end end
# app/controllers/posts_controller class PostsController < ApplicationController load_and_authorize_resource end
And that’s it as far as controllers go. What about views, though?
Let’s say you want admins and moderators to be the only ones to see the delete button for the post (within the post partial).
# app/views/posts/_post.html.erb <% if can? :destroy, post %> <%= link_to 'Delete', post, method: :delete, class: 'btn btn-danger' %> <% end %>
This is so much better than checking a user’s class without understanding what the context for the check is.
Something to remember, though: CanCanCan’s automagic-ness relies on standard Rails naming practices. If, however, you find yourself breaking the standard a bit, the gem offers plenty of options to work with almost any situation.
I can not recommend this gem enough to anybody designing a web app with multiple user types. CanCanCan is a real gem of a gem, especially if you use Devise.