Ruby on Rails - Intermediate Ruby on Rails - Sprint Challenge - MusicLib

Intro

The musiclib app is a partially completed API that will power client apps similar to something like Spotify. Your job is to continue adding functionality, specifically to add the concept of playlists for users.

Data Model

Here is a breakdown of the existing data model for the application:

User

attribute	type
id	integer
email	string
api_key	string
created_at	datetime
updated_at	datetime

Artist

attribute	type
id	integer
name	string
created_at	datetime
updated_at	datetime

Album

attribute	type
id	integer
name	string
available	boolean
artist_id	integer
created_at	datetime
updated_at	datetime

Song

attribute	type
id	integer
title	string
track_number	integer
length_seconds	integer
album_id	integer
created_at	datetime
updated_at	datetime

Resources

Here is a breakdown of the existing resource API for the application:

verb	resource	route	controller#action	note
GET	album	/api/v1/albums	api/v1/albums#index	list all available albums
GET	album	/api/v1/artists/:artist_id/albums	api/v1/albums#index	list all available albums for a specific artist
GET	album	/api/v1/albums/:id	api/v1/albums#show	get a specific album
GET	artist	/api/v1/artists	api/v1/artists#index	list all artists
GET	artist	/api/v1/artists/:id	api/v1/artists#show	get a specific artist
GET	song	/api/v1/songs	api/v1/songs#index	list all songs
GET	song	/api/v1/albums/:album_id/songs	api/v1/songs#index	list all songs for a specific album
GET	song	/api/v1/songs/:id	api/v1/songs#show	get a specific song
GET	user	/api/v1/users	api/v1/users#index	list all users
POST	user	/api/v1/users	api/v1/users#create	create a new user
GET	user	/api/v1/users/:id	api/v1/users#show	get a specific user

Get Started

Clone the app and run bundle install. Then, create, migrate, and seed the database.

Run rails server and test endpoints

Start up the rails server and test out some of the endpoints:

list albums
list an artist's albums
get an album
list artists
get an artist
list songs
list an album's songs
get a song

Step One - Add Playlist Routes and Controller

Playlist Routes

The client dev team has requested the following routes be made available for playlists and playlist songs. Add these routes to the musiclib application.

verb	resource	route	controller#action	note
GET	playlist	/api/v1/playlists/:id	api/v1/playlists#show	get a specific playlist
GET	playlist	/api/v1/user/:user_id/playlists	api/v1/playlists#index	list all playlists for a specific user
POST	playlist	/api/v1/user/:user_id/playlists	api/v1/playlist#create	create a playlist for a specific user
GET	song	/api/v1/playlist/:playlist_id/songs	api/v1/songs#index	list all songs
POST	song	/api/v1/playlist/:playlist_id/songs	api/v1/songs#create	add a song to a playlist

Add the playlist route to show a specific playlist.
Nested within the user resource, add the playlist routes to list and create playlists.
Nested within the playlist resource, add the song routes to list and create songs.
Limit routes to only the ones expected by the client app team.

Playlist Controller

Create playlist controller and implement the index, create and show actions to respond to the routes you created.

index should only work if nested under user.
show should only work without nesting.
create should only work if nested under a user.

Step Two - Add Playlist and PlaylistSong Models

Playlist

attribute	type
id	integer
name	string
user_id	integer
created_at	datetime
updated_at	datetime

PlaylistSong

attribute	type
id	integer
playlist_id	integer
song_id	integer
created_at	datetime
updated_at	datetime

Playlist Migration and Model

We need to add a playlist model to the app so that users can create playlists and add songs to them.

Add a Playlist ActiveRecord model to the app.
Create and run a migration to set the attributes of the playlist model in the database to match the table above.
Add a validation to the model that ensures playlists always have names.

PlaylistSong Migration and Model

We need a way to associate songs and playlists but we can't do it directly because songs can belong to many playlists and playlists can have many songs. So we'll use an intermediary model to represent the concept of a 'playlist song' to capture the relationship and store it in the database.

Add a PlaylistSong ActiveRecord model to the app
Create and run a migration to set the attributes of the playlist model in the database to match the table above

Playlist Associations

Now, we need to set up the various active record associations in the model files to let rails now how our playlist and playlist songs related to themselves and other models.

Add an association to user represting that it can have many associated playlists
Add an association to playlist represting that it can have many associated playlist_songs
Add an association to playlist represting that it can have many songs via the playlist_songs association
Add associations to playlist_song represting that a playlist_song belongs to both a playlist and a song
Add associations to song represting that they can have many playlist_songs and have_many playlists via playlist_songs

Step Three - Refactor and Improve Implementation

Move album length_seconds to model

The length_seconds value in the Albums controller is calculated directly in the controller and is unavailable to the rest of the application. Writing code like this inside the controller makes it impossible to reuse and is generally considered a bad practice. Since it works based on an instance of a model, let's convert the functionality to an instance method on the Album model.

Add a length_seconds method to the model and convert the call in the controller.

The starting code:

album.songs.reduce(0) { |length, song| length + song.length_seconds }

The ending code:

album.length_seconds

The method should total up all of the songs' length_seconds on an album.

Extract song sorting into a service object

Like the length_seconds value, the sorting of songs is done in the song controller. This behavior is not reusable by the rest of the system. Because sorting is done against the list of songs, and not an individual song, it doesn't make sense to move into the model. Let's extract a service object called SongSorter. It should be placed in the app/services directory and should be initialized with two arguments: 1) the list of songs and 2) the sort value. It should have one method named sort which returns the sorted songs.

Create SongSorter in app/services.
Instantiate and call sort on SongSorter in the SongsController instead of the current conditional block.
The sorting should work regardless of whether you are listing by album, playlist, or all songs.

Convert Query to Scope and Improve Performance

The album#index controller action has two queries that order by the album name and searches for only albums that are available. This common query should be converted into a scope on album named available that lists only available albums ordered by name.

Convert album query to scope named available.
Use available scope instead of the where and order queries for both albums and artist's albums.

The query also results in an n+1 query because each album's songs are loaded after querying for the list of albums. Prevent this n+1 query in the controller by including the songs in the query.

Solve inefficient n+1 query by including songs

Step Four - Write Specs for Album

Write model specs for Album

The spec/models/album_spec.rb file has 5 tests that need to be written.

Test that an album can be valid when properly set up
Test that an album is invalid without a name
Test that an album has exactly the expected attributes
Test that the available scope returns expected results from the database
Test that the length_seconds method returns expected length

Write request spec for showing an album

The spec/requests/api/v1/albums/get_album_spec.rb needs to be completed by testing that the expected album is successfully returned from the endpoint.

Uncomment the routes spec and run the full spec suite

Uncomment the file located spec/routing/api/v1/api_routes_spec.rb and run the full spec suite. This file tests the routes that are defined in config/routes.rb and ensures they go to the appropriate controller. If all of the routes for playlist and songs were properly added, this spec should pass.

McTrip777/rails-mini-course-sprint2-challenge-musiclib--starter