Ruby Object Relations: Has-Many-Through Lab

Objectives

• Write classes that are related to each other via the "has-many-through" relationship.
• Write methods that use the "has-many-through" relationship to deliver information on related objects.

Overview

In this lab, we'll be dealing with two sets of three classes.

We have a Song, Artist and Genre class. Songs belong to an artist and belong to a genre. A genre has many songs and an artist has many songs. An artist has many genres through its songs and a genre has many artists through its songs.

We also have an Appointment, Doctor and Patient class. Appointments belong to a Patient and a Doctor. A Doctor has many Appointments and a Patient has many Appointments. A Doctor has many Patients through its Appointments and a Patient has many Doctors through its Appointments.

Instructions

Start with the Artist/Song/Genre domain.

The Artist model:

• The Artist class needs a class variable @@all that begins as an empty array
• The Artist class needs a class method .all that lists each artist in the class variable
• An artist is initialized with a name and is saved in the @@all array.
• The Artist class needs an instance method, #new_song, that takes in an argument of a name and genre creates a new song. That song should know that it belongs to the artist.
• The Artist class needs an instance method, #songs, that iterates through all songs and finds the songs that belong to that artist. Try using select to achieve this.
• The Artist class needs an instance method, #genres that iterates over that artist's songs and collects the genre of each song.

madonna = Artist.new("Madonna")

The Genre model:

• The Genre class needs a class variable @@all that begins as an empty array.
• The Genre class needs a class method .all that lists each genre in the class variable.
• A genre should be initialized with a name and be saved in the @@all array.
• The Genre class needs an instance method, #songs, that iterates through all songs and finds the songs that belong to that genre.
• The Genre class needs an instance method, #artists, that iterates over the genre's collection of songs and collects the artist that owns each song.

pop = Genre.new("pop")

The Song model:

• The Song class needs a class variable @@all that begins as an empty array.
• The Song class needs a class method .all that lists each song in the class variable.
• A song should be initialized with a name, an artist, and a genre, and be saved in the @@all array.

madonna = Artist.new("Madonna")
pop = Genre.new("pop")

into_the_groove = Song.new("Into the Groove", madonna, pop)

Now let's move on to our Doctor/Appointment/Patient domain model.

Note: the tests will be calling your #new_appointment methods in your Doctor and Patient classes, as well as the #initialize method in the Appointment class. Therefore, in order to pass the tests, you will need to make sure that your method definitions specify the parameters in the order indicated below.

The Doctor model:

• The Doctor class needs a class variable @@all that begins as an empty array.
• The Doctor class needs a class method .all that lists each doctor in the class variable.
• A doctor should be initialized with a name and be saved in the @@all array.
• The Doctor class needs an instance method, #new_appointment, that takes in a date and an instance of the Patient class in this order, and creates a new Appointment. That Appointment should know that it belongs to the doctor
• The Doctor class needs an instance method, #appointments, that iterates through all Appointments and finds those belonging to this doctor.
• The Doctor class needs an instance method, #patients, that iterates over that doctor's Appointments and collects the patient that belongs to each Appointments.

doogie = Doctor.new("Doogie Howser")

The Patient model:

• The Patient class needs a class variable @@all that begins as an empty array.
• The Patient class needs a class method .all that lists each patient in the class variable.
• A patient is instantiated with a name and be saved in the @@all array.
• The Patient class needs an instance method, #new_appointment, that takes in a date and an instance of the Doctor class in this order and creates a new Appointment. The Appointment should know that it belongs to the patient.
• The Patient class needs an instance method, #appointments, that iterates through the Appointments array and returns Appointments that belong to the patient.
• The Patient class needs an instance method, #doctors, that iterates over that patient's Appointments and collects the doctor that belongs to each Appointment.

ferris = Patient.new("Ferris Bueller")

The Appointment model:

• The Appointment class needs a class variable @@all that begins as an empty array.
• The Appointment class needs a class method .all that lists each Appointment in the class variable.
• An Appointment should be initialized with a date (as a string, like "Monday, August 1st"), a patient, and a doctor in this order. The Appointment should be saved in the @@all array.

ferris = Patient.new("Ferris Bueller")
doogie = Doctor.new("Doogie Howser")

new_appointment = Appointment.new('January 1st, 1989', ferris, doogie)