learn-co-curriculum / fewpjs-oo-complex-class-relationships-lab

Complex Class Relationships Lab

Learning Goals

• Practice building complex class relationships

Introduction

In the previous lab, we built classes to represent Song, Artist and Genre. In this lab, we're going to expand on the previous solution. This time, we will add albums as well as some additional behaviors for our Artist class.

Instructions

For this application, individual songs will be used to keep track of its artist and genre, just as before. The new Album class will contain collections of songs. The new Artist class will also contain some additional behaviors, but these should be added last, as they will rely on Album.

• The Genre class should take in one parameter, name and assign it to a private property, _name. Genre should have a getter, name that returns _name.

• The Artist class should also take in one parameter, name, and assign it to a private property, _name. Artist should have a getter and setter for name to return or modify _name.

• The Song class should take in three parameters, a title, an instance of an artist, and an instance of a genre. These should be assigned to three private properties, _title, _artist, and _genre. Song should have a caption getter that takes the title, artist name and genre name and interpolates them into a single sentence.

  let queen = new Artist('Queen');
  let popRock = new Genre('Pop Rock');
  let dontStopMeNow = new Song("Don't Stop Me Now", queen, popRock);
  dontStopMeNow.caption;
  // => 'Don't Stop Me Now by Queen (Pop Rock)'

• The Album class should take in a title, an instance of an Artist and an array of Song instances, an assign these to private properties. Album should have getters for title, songs, and artist.

  • Write a trackList getter that returns an array of the album's song titles.
  • Write a genres getter that returns an array of genres from the album's list of songs. All array elements should be unique (no repeating genres).

Expanding Artist

Once you have all tests passing for the Album class, let's add a few more features to Artist:

• Add a private property, _albums, that starts as an empty array.
• Create a getter and setter for albums that will either return an array of Album instances, or take in an array of Albums and assign it to the _albums property.
• Create a discography getter that returns the title of each album belonging to an artist
• Create a songs getter that returns an array of all Song instances from all albums belonging to an artist

Conclusion

With Object Orientation, we can build complex dependencies. These dependencies may rely on classes one or two degrees removed (as we see getting songs for an artist through albums). Dependencies can also be bi-directional - an Album can have an artist and an Artist can have albums.

It is important to understand how to create these complex dependencies, but in general, it is recommended that you only create dependencies you absolutely need. The more complex your dependencies, the less flexible your classes will get (and therefor, the harder to change and maintain later on).

As we build more complex dependencies, we also need to make sure our data is kept consistent. In this case, albums have an artist and artists have many albums, but we needed to add additional code to make sure both are updated when an album is created.