This article is also published in Iqbal’s blog here.
Where were we?
In the previous part, we have used Devise library to create our User model in CRUD style. With what we have coded in the previous part, you should now be able to manage users and authenticate them. Now it’s time to add the roles and define what features they may access.
1. Adding the Roles
This step is pretty traditional, we can just scaffold all the MVC part for our roles. In this article, I only need one attribute that is the name of the role.
rails generate scaffold Role name:string
2. Making HABTM relationship between roles and users
We have to do several tasks in this step. The first thing is to manually create the migration file for the habtm table. We do it by first generating the migration file like this:
rails generate migration UsersHaveAndBelongToManyRoles
and then we fill the file with this code:
class UsersHaveAndBelongsToManyRoles < ActiveRecord::Migration
create_table :roles_users, :id => false do |t|
t.references :role, :user
And do not forget to modify our model files. This is how our role.rb looks like after we modify it:
class Role < ActiveRecord::Base
And this is how our user.rb file looks like. Please be noted that we also add :role_ids in the attr_accessible and we add a method to identify the role of the respective user.
class User < ActiveRecord::Base
# Include default devise modules. Others available are:
# :token_authenticatable, :confirmable, :lockable and :timeoutable
:recoverable, :rememberable, :trackable, :validatable
# Setup accessible (or protected) attributes for your model
attr_accessible :email, :username, :password, :password_confirmation, :remember_me, :role_ids
In the views part, we have to modify at least the _form.html.erb from our users view so that we can assign the role to the user from web interface. This is how the file users/_form.html.erb looks like:
<%= form_for(@user) do |f| %>
<% if @user.errors.any? %>
<%= pluralize(@user.errors.count, "error") %> prohibited this user from being saved:
<% @user.errors.full_messages.each do |msg| %>
- <%= msg %>
<% end %>
<% end %>
<%= f.text_field :email %>
<%= f.text_field :username %>
<% if @current_method == "new" %>
<%= f.password_field :password %>
<%= f.password_field :password_confirmation %>
<% end %>
<% for role in Role.find(:all) %>
<%= role.name %>
<% end %>
<% end %>
Of course you can also modify your index.html.erb and show.html.erb files to show the role of the listed user(s). But I think I leave it to you to do it yourself. After all these tasks, we can run rake task db:migrate.
In this state, we can now add users and assign them with the roles we desire. But of course each role has not yet identified with any permission by CanCan. That’s what we’re going to do in the next step.
3. Adding ability
To use CanCan, we have to make a class that defines the permissions that are given to each role. In CanCan, this is called as “ability” and to set it up, we have to create the ability.rb file as part of our models.
user ||= User.new # guest user
if user.role? :administrator
can :manage, :all
elsif user.role? :operator
can :manage, Post
can :read, :all
CanCan use a very pleasant way to describe our roles and it’s corresponding allowed features. In our code above, we use the keyword “can” and then follow it with the level of authorization we want the respective role to have and at last we end it with the name of the model. The level of authorizations that I have tried so far is :create, :read, :update, :delete, and :manage. Maybe there is a way to define another ability, you can find about it in depth in the official Github page of CanCan library here.
4. Adding authorization
Finally, in every controller that needs authorization, we add this line:
I think that’s it for now. I know I only have covered the basic part of using Devise and CanCan but I hope this can be helpful for anyone that just starts to learn about both libraries. I may add a working source code to this tutorial later. Meanwhile, if you have any trouble following this tutorial, you can ask me in the comment section.