- Build out the has many/belongs to relationship between two classes.
- Build methods that use the has many/belongs to relationship between two classes.
- Use a class variable to track data about a class.
- Build a class method to expose data stored in a class variable.
In this lab, we'll be dealing with two sets of classes. The Artist and Song class and the Author and Post class. An artist should have many songs and a song should belong to an artist. An author should have many posts and a post should belong to an author.
Because of the has many/belongs to relationship between your classes, the Artist tests, i.e. the tests in spec/artist_spec.rb, rely on some code in the Song class and vice versa. The same is true of the tests for the Author and Post classes. So, as you proceed through solving this lab, you will go back and forth between coding in Artist and Song and between coding in Author and Post.
We recommend starting out by getting some of the initial Artist tests passing and switching to write code in the Song class as directed by the test output. Then, once your Artist and Song tests are passing, do the same for Author and Post.
This lab is primarily test-driven. So run the test suite with the learn command to get started. Read the test output very carefully to help guide you through. First, read through the guidelines below and refer back to them as you complete the lab.
How can an artist have many songs and a song belong to an artist? An individual song will need to have an artist=() and artist method and an individual artist will need to be initialized with an empty collection of songs.
How can an author have many posts and a post belong to an author? An individual post will need to have an author=() and author method and an individual author will need to be initialized with an empty collection of posts.
To get the tests on these methods passing, you'll need to define methods that take in an argument of a name (or title), use that argument to create a new song (or post) and then associate the objects.
For add_post_by_title, you'll want to make sure the body of the method associates the newly created post with an author and adds the post to the author's collection.
Build the methods some_song.artist_name and some_post.author_name that return the names of the artist and author of the given song and post respectively.
These methods should use, or extend, the has many/belongs to relationship you're building out. If a song has an artist, you can call: some_song.artist and return an actual instance of the Artist class. Since every artist has a name, some_song.artist.name should return the name of the Artist instance associated with the given song. Your #artist_name method should utilize this relationship.
Note: We like our code to be robust, i.e. not easily breakable. Make sure your #artist_name and #author_name methods will not break if the given song or post does not have an artist or author. In this case, your methods should return nil.
You'll be required to write a class method that tracks the total number of songs, tallied up from all of the existing artists. You'll be required to write a similar method for the Author class.
How do we keep track of data regarding an entire class? With class variables! The Artist class should have a class variable, @@song_count. This variable should start out set equal to 0. When should you increment this value? Anytime a new song is added to an artist. Your .song_count method should then return the value of the @@song_count variable. Build out the same logic for your Author class.
View Ruby Objects Has Many Lab on Learn.co and start learning to code for free.
React
Typescript
Django
Laravel
Facebook
Microsoft
Google
Alibaba
D3
Tencent