You're going to be implementing a Music Library domain composed of 3 main models, Song, Artist, and Genre that will relate to each other and collaborate heavily. Additionally, you're going to be extracting some common functionality of those models into a module, Concerns::Findable and mixing that module into those classes. You'll then build a collaborating object, MusicImporter, that can parse a directory of MP3 files and use the filenames to create instances of Song, Artist, and Genre. Finally, you'll build a CLI in bin/musiclibrary that is powered by a MusicLibraryController to provide a simple CLI that lets a user browse the library of MP3s imported by song, artist, and genre.

This is a complex lab with many parts, go slow, try to understand what you're trying to build holistically before starting. Read this entire README before jumping in. As you go from spec to spec, we recommend doing them in numbered order.

A quick note on the placement of Modules. It's Ruby convention to put all Modules in a concerns folder and to be namespaced like this Concerns::ModuleName.

The first thing to do is get the basics of the main models working. Each model has almost the exact same basic requirements, so once you make 001_song_basics_spec.rb pass by building the Song class, the Artist and Genre basic specs will go fast.

The requirements of each model are that they can accept a name upon initialization and set that property correctly. The name property should be readable and writeable by the object.

Song.new("Blank Space").name #=> "Blank Space"`

Additionally, each class should contain a class variable @@all that is set to an empty array and is prepared to store all saved instances. This class variable should be accessible via the class method .all.

Song.all #=> []

Instances should respond to a #save method that adds the instance itself into the class variable @@all.

Song.new("Blank Space").save
Song.all #=> [#<Song: @name="Blank Space">]

The class should be able to empty its @@all array via a class method .destroy_all.

Song.new("Blank Space").save
Song.all #=> [#<Song: @name="Blank Space">]
Song.destroy_all
Song.all #=> []

Finally, all classes should implement a custom constructor .create that instantiates an instance using .new but also evokes #save on that instance, forcing it to persist immediately.

Song.new("Blank Space")
Song.all #=> []
Song.create("Blank Space")
Song.all #=> [#<Song: @name="Blank Space">]

• Songs belong to an Artist and an Artist has many songs. Adding a song to an Artist is done by calling an #add_song method on an instance of the Artist class
• Songs can be initialized with an optional Artist argument

• Genres have many songs and are initialized with an empty list of songs
• Songs have one genre
• Songs can be initialized with an optional genre

• Artists have many Genres through Song. Implement a #genres method for this association.
• Genres have many Artistss through Song. Implement a #artists method for this association.

First implement the following two methods in your Song class

• Songs should have a find_by_name method.
• Songs should have a find_or_create_by_name method.

Now that you've done that, let's generalize those methods by putting them into a module and then including that module in the Genre and Artist class.

• Implement a generic #find_by_name method that uses the .all method defined by the class to find by name.
• Implement a generic #find_or_create_by_name method that uses the .all method defined by the class.
• Add this module to your Genre and Artist class.

Create a Music Importer class to work with your Song, Genre and Artist objects to import a directory of mp3s. This class will have the following methods:

• Initialize accepts a file path of mp3 files
• A #files method that will return all of the filenames
• Add a new method to the Song class called .new_from_filename that creates a Song based on a filename
• Add a new method to the Song class called .create_from_filename that creates a Song based on a filename and saves it to the @@all class variable
• In your MusicImporter class, add an .import method that imports all the files from the library and creates the Song objects.

Congrats! You've done the heavy lifting. Now let's wrap it all up in a CLI so that users can actually interact with our code.

• It initializes with an optional path to the music, but defaults to ./db/mp3s. It creates a MusicImporter and imports the music.
• Add a #call method that starts the CLI and asks the user for input. Check out the tests for specifics.

QA with Students

• This Q&A led by Avi Flombaum covers setting up a bin file, setting up a Gemfile and installing gems, and identifying objects and their responsibilties. There are general tips on requirements, gems, and design.

Debugging an Error in Music Library CLI

• This walkthrough traces an error to its source in the code. In addition it covers how to change file permissions, and create an executable file to initialize a sandbox environment.

Lab Review

View Music Library CLI on Learn.co and start learning to code for free.