Sinatra Url Shortener With Users

Learning Competencies

• Use Active Record Associations
• Integrate multiple code bases into one coherent application
• Implement a user authorization scheme to limit unauthorized access to specific pages in a web application

Summary

Let's integrate our URL shortener with our user authentication code. This will let people save the URLs they've shortened and open up the possibility of "private" short URLs.

This will be the most complex web application you've worked on so far; take it one step at a time. If the problem seems unassailable, break it down into simpler parts you understand. If you don't see how to break it down, flag down a staff member and ask: "How do I break this down into something that makes more sense for me?"

Releases

Release 0: Glue together!

Start by gluing together your user authentication code and your URL shortening code as best you can. This means creating the relevant migrations, models, and controller code.

The core flow of the URL shortener should remain the same, however a person might choose to log in or create an account. In the event that they're logged in when they shorten a URL, this Url should now be associated with their user account. In other words, a Url belongs to a User and a User has many Urls.

Note: Don't worry about implement the above user-centric logic yet. First get all the URL shortening and user authentication code working. Make sure people can log in and can shorten URLs regardless of whether they're logged in or not.

In this case, you might want multiple controllers. Something like this would be reasonable:

1. app/controllers/urls.rb, which contains the routes related to listing, creating, and redirecting Url objects
2. app/controllers/sessions.rb, which contains the routes related to logging in and logging out
3. app/controllers/users.rb, which contains the routes related to creating, displaying, and editing users

Release 1: Logged in, logged out, and current user

People should be able to create short URLs regardless of whether they're logged in or not. That is, the user_id field on the urls table could possible be NULL.

However, if a user is logged in, when we create a URL it should set the user_id to whatever the user_id of the currently logged-in user is. This information should not be a part of the form that a user submits — it would be trivial for someone to change the content of the form and submit as any user.

Instead, create a users helper at app/helpers/user.rb. It should contain a method that works like this:

helpers do
  # This will return the current user, if they exist
  # Replace with code that works with your application
  def current_user
    if session[:user_id]
      @current_user ||= User.find_by_id(session[:user_id])
    end
  end

  # Returns true if current_user exists, false otherwise
  def logged_in?
    !current_user.nil?
  end
end

Your controller can now call current_user to get the currently authenticated user, if they exist. This means we don't have to rely on user-submitted data to determine what user created a short URL.

Release 2: Profile Page

Create a profile page for each user like so:

get '/users/:id' do
end

This should display all the links that a particular user has created. If I'm viewing my own profile page, show the number of clicks next to each link so I can see how awesome my link-sharing skills are.

Resources

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