Authentication with Devise and cancancan in Rails

To use the cancancan gem with devise in a Ruby on Rails app, you will need to do the following:

First, you need to add the cancancan gem to your Gemfile and run bundle install.

Then create a Ability model by running the following command:

rails g cancan:ability

This will create a new file at app/models/ability.rb that contains the Ability class.

In the Ability class, define the permissions for different user roles. For example:

class Ability
  include CanCan::Ability

  def initialize(user)
    if user.admin?
      can :manage, :all
    else
      can :read, :all
    end
  end
end

In your controllers, use the load_and_authorize_resource method to load and authorize the resource. For example:

class PostsController < ApplicationController
  load_and_authorize_resource

  def show
    # The @post instance variable has already been loaded and authorized
  end
end

In your views, use the can? method to show or hide content based on the user’s permissions. For example:

<% if can? :update, @post %>
  <%= link_to 'Edit', edit_post_path(@post) %>
<% end %>

I hope this helps! Let me know if you have any questions.