bhabig/cancan_lab-v-000

CancanCan Secret Notes

Objectives

1. Understand how to create an Ability class.
2. Learn how to model permissions in the database.
3. Prevent users from accessing certain actions from the controller.
4. Prevent users from seeing certain pieces of the view.

Overview

We're going to learn how to integrate CanCanCan into a Rails application. Our authorization model for this example will be a message board for secret notes.

Instructions

1. Create a User model and migration. Users have names and that's it.

We could give our users passwords quite easily with has_secure_password. However that would make it a lot more annoying to develop this app! For now, we'll just have usernames, and we'll let anyone sign in as someone else only using their name. This will make it easy to switch between accounts and test our authorization scheme.

2. Create a Note model. Notes have content, and a user, their creator.

3. Create a Viewer model. viewers is a join between notes and users. An entry in the Viewers table means that user can view that note.

Hint: There are a few ways to set up the relationship between Notes and Users. Here's what the tests expect:

# user.rb
has_many :viewers
has_many :readable, through: :viewers, source: :note

# note.rb
has_many :viewers
has_many :readers, through: :viewers, source: :user

When we create a new note, we'll want a form that takes in a comma-separated list of usernames which represent who that note is visible to. We'll use utility methods on the note model which should know how to create the relationship between a note and its viewers. These readers and writers will be called visible_to and visible_to=. You should be able to use the same principles of mass assignment and "accepts_nested_attributes" to accomplish this. Use the tests as your guide.

4. Create controllers. We'll need a SessionsController, a UsersController, and a NotesController. UsersController just needs a create route. NotesController should have the full CRUD suite. Your SessionsController will be logging in and out users using the principles we learned earlier in this unit (but we won't use a password only a username).

5. Add CanCanCan to your Gemfile.

6. Generate a skeleton Ability model with rails g cancan:ability. Write rules in the Ability model. If you need help on composing rules, the documentation here is good.

The rules are a little bit tricky because you have to look through an association to figure out if a user can read a note. You'll want to use a block condition, like this:

can :read, Note do |note|
  # TODO
end

If your ActiveRecord relationships have been set up right, this should be fine.

Now, go through the remaining tests and ensure they pass. To pass the controller tests, make calls to authorize! or load_and_authorize_resource in your NotesController.

can :read, Note do |note|
  # TODO
end

Resources

Sitepoint - CanCanCan: The Rails Authorization Dance

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