Tweeter

In this project, we'll learn how to build a social network. It will be a simple clone of Twitter.

To get started, we'll create Users with Devise and Statuses (tweets) with Starter Generators. A user has many statuses, a status belongs to a user.

So Far

The steps I took so far in the application are:

1. rails new tweeter

2. Add the devise and draft_generators gems to the Gemfile.

3. rails generate devise:install

4. rails generate devise user username

5. rails generate draft:resource status content:string user_id:integer

6. rake db:migrate

7. rails generate draft:layout

8. Set the homepage root 'statuses#index' in config/routes.rb.

9. Force someone to be signed in at all times in app/controllers/application_controller.rb:

   before_action :authenticate_user!
   

10. rails generate devise:views

11. Add an input for username to both app/views/devise/registrations/new.html.erb and app/views/devise/registrations/edit.html.erb:

    <div class="field">
      <%= f.label :username %><br />
      <%= f.text_field :username %>
    </div>
    

12. Allow username through security in app/controllers/application_controller.rb:

    before_action :configure_permitted_parameters, if: :devise_controller?
    
    protected
    
    def configure_permitted_parameters
      devise_parameter_sanitizer.permit(:sign_up, :keys => [:username])
    
      devise_parameter_sanitizer.permit(:account_update, :keys => [:username])
    end
    

13. Add one-to-many associations:

14. User has many statuses, Status belongs to user.

15. Add validations:

16. User usernames should be unique.

17. Status content should be present.

18. Status user should be present.

19. Automatically associate statuses to signed-in user: remove user_id <input> from users#new and users#edit forms, and instead assign directly in the create and update actions:

    @status.user_id = current_user.id
    @status.content = params[:content]
    

20. Replace raw foreign keys with usernames in statuses#index and statuses#show.

21. Fix the navbar to show sign-out and edit profile links at the appropriate time in app/views/layouts/application.html.erb.

22. Some visual formatting; replaced Pinterest-style layout with a simple table.

Setup

1. Clone.
2. bundle install
3. rake db:migrate
4. rake db:seed
5. Click Run Project in Cloud9
6. Navigate to your app preview
7. Sign in with the user "alice@example.com", password "12341234".
8. You should see a list of random tweets.

Adding Friend Requests

At this stage, we have an app where users can sign in and add statuses, but the index page just shows a list of all statuses globally.

What we want instead is the ability for users to follow other users, and narrow the index of statuses to only show the ones that belong to people that I follow.

So, we need a many-to-many relationship between Users and Users. Like any many-to-many, this means we need a join model, which will have two foreign key columns, and we'll establish two one-to-many relationships first.

Generate the join model

I'm going to call the join model "friend requests". Each row in this table will represent the connection between two users.

rails generate draft:resource friend_request sender_id:integer receiver_id:integer

Notice that since I can't have two columns both called user_id, I've made up two different and descriptive column names instead.

Next, as usual, we should immediately add our validations and one-to-many relationships:

# app/models/friend_request.rb
belongs_to :sender, :class_name => "User", :foreign_key => "sender_id"

belongs_to :receiver, :class_name => "User", :foreign_key => "receiver_id"

validates :sender, :presence => true, :uniqueness => { :scope => :receiver }
validates :receiver, :presence => true

Notice the uniqueness validation on :sender ensures that you can't accidentally follow the same person twice.

The associations in FriendRequest are pretty straightforward; we just have to use the non-shortcut form of belongs_to so that we can specify a column name that's different from the default for each one-to-many.

The has_manys in User are slightly trickier, but not bad:

# app/models/user.rb
has_many :friend_requests_where_sender, :class_name => "FriendRequest", :foreign_key => "sender_id"

has_many :friend_requests_where_receiver, :class_name => "FriendRequest", :foreign_key => "receiver_id"

So, now each User has many friend_requests_where_sender as well as many friend_requests_where_receiver.

The last step is to establish the many-to-many on top of these two one-to-manies:

# app/models/user.rb
has_many :friend_requests_where_sender, :class_name => "FriendRequest", :foreign_key => "sender_id"

has_many :friends_where_sender, :through => :friend_requests_where_sender, :source => :receiver


has_many :friend_requests_where_receiver, :class_name => "FriendRequest", :foreign_key => "receiver_id"

has_many :friends_where_receiver, :through => :friend_requests_where_receiver, :source => :sender

So we're saying: when someone calls .friends_where_receiver on me, walk through the friend_requests table to find the people who sent me requests (in other words, my followers). Vice versa when someone calls .friends_where_sender (in other words, people that I follow).

Finally, let's set up one more :through association to make our lives really easy:

# app/models/user.rb
has_many :timeline_statuses, :through => :friends_where_sender, :source => :statuses

This additional method will walk directly through the people that I follow to their statuses, which is the main thing that we want.

That's it for the setup. Now let's use these powerful associations to make our app do what we want:

1. On the friend_requests#new form, let's get rid of the <input> for sender_id and instead associate it automatically in the create and update actions to current_user.

2. Narrow the statuses#index to only show statuses from people that the current user is following:

   def index
     @statuses = current_user.timeline_statuses.order("created_at DESC")
   end
   

That's it! If you want to, you can also place a follower count (current_user.friends_where_receiver.count) and following count (current_user.friends_where_sender.count) in a sidebar or something.

Solutions

A completed version is here.