Lesson Tuesday

Our record store now has routing for albums, which is a good start, but most applications have more complicated routing. We'll add songs to our albums to demonstrate. Keep in mind that this is often a difficult concept at first. It may take a few weeks for nested routing to click but it should make much more sense by the time we begin working with Rails.

Each album can have many songs and each song will belong to an album. This is known as a one-to-many relationship. Adding artists is more complicated because an artist can have many albums and an album can have many artists, which is known as a many-to-many relationship. We'll be covering these relationships much more in-depth in the next course section when we get into databases — and we'll also cover other kinds of relationships between objects as well. For now, let's keep our focus on routing.

In order to properly reflect this one-to-many relationship in our application, we'll use nested routing. Let's take a look at the routes we could use for adding song CRUD functionality:

HTTP RESTful routing table for CRUD for songs

It should be clear why these are called nested routes; songs are nested inside of albums and can only be accessed within the context of an album. By nesting songs within albums, we ensure that songs will always have access to a specific album's id — this makes it easier to associate songs and albums in our mock database (and eventually real databases as well). This type of routing is commonly used in Rails, too, which is a key reason why we are exploring it further now.

There are several advantages to this kind of routing. Here are a few:

  • The routes are self-explanatory. It's clear from the routes above that songs should belong to albums. Having consistent naming like this makes our code easy to read and understand.
  • By nesting songs within albums, we ensure we will always have access to an album's id. This makes it easy to associate an album with a song. The reason for this will become clear in the next lesson.

There are also disadvantages to this kind of routing as well. Nested routes can quickly become difficult to work with, especially when routes are more than two layers deep. For instance, it would be challenging to work with a route like albums/:id/songs/:id/lyrics/:id. This is considered a code smell and should be avoided.

In the next lesson, we'll create CRUD functionality in our backend logic for adding songs to albums.


One-to-many relationship: When many instances of an object belong to one instance of another object. For instance, in first grade a Teacher could have many Students but Students would have only one Teacher.

Many-to-many relationship: When many instances of an object can belong to many instances of another object. For instance, in high school a Teacher could have many Students and Students could also have many Teachers.

Nested routing: When we create routes that depict a "belongs to" relationship.

Example Nested Routes

HTTP verb Route CRUD Action Description URL
GET /albums/:id/songs READ Get a list of all the songs on an album. www.bestundergroundrecords.com/albums/72/songs
GET /albums/:id/songs/:song_id READ Look at the detail page for a single song. www.bestundergroundrecords.com/albums/72/songs/51
POST /albums/:id/songs CREATE Add a new song to an album. www.bestundergroundrecords.com/albums/72/songs
PATCH /albums/:id/songs/:song_id UPDATE Update a single song. www.bestundergroundrecords.com/albums/72/songs/51
DELETE /albums/:id/songs/:song_id DELETE Delete a song from an album. www.bestundergroundrecords.com/albums/72/songs/51

Lesson 25 of 37
Last updated August 7, 2022