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Chapter 13 - Adding Books and Authors

In this chapter, we will be focusing on completing the basic set of models we need before creating any endpoint. To accompany the Publisher model, we are going to create the Book and Author models. Finally, we will update the Publisher model since it's currently incomplete.

The Author Model

Run the corresponding model generator:

rails generate model Author given_name:string family_name:string

Execute the migration:

rails db:migrate && rails db:migrate RAILS_ENV=test

The Book Model

Run the corresponding model generator:

rails generate model Book title:string subtitle:text isbn_10:string:uniq \
isbn_13:string:uniq description:text released_on:date \
publisher:references author:references

Open the generated migration file and an index to the following attributes: title, isbn_10, isbn_13, publisher_id, and author_id.

  • Both isbn_10 and isbn_13 have to be unique!

### CORRECTION ###

The uniqueness constraint was not properly added when generating the Book model and I've added a fix for it. You can also edit the migration file like the in the example below, if you already ran the migration and don't want to rollback:

t.string :isbn_10, index: { unique: true }
t.string :isbn_13, index: { unique: true }

I was able to find that error thanks to Rubocop. You can also read more about it on this greate ThoughtBot Article.

### CORRECTION ###

Execute the migration:

rails db:migrate && rails db:migrate RAILS_ENV=test

Associations

We have three different models (Publisher, Author, and Book) that are related.

Author Associations

Publisher Associations

Book Associations

We need to add required: false for an optional association. Publishers are optional since authors can self-publishe their books. In that case, publisher should be nil.

Handling Book Covers

Uploading files to a Web API is a bit different from using an HTML form and the multipart/form-data media type.

Since any client should be able to send images to our API, we are going to use a different approach that will work the same way on both mobile and JavaScript applications. The idea is simply to enconde the file in the client in Base64, send it, and let the server decode it and store it.

For this purpose, we're going to use carrierwave and carrierwave-base64

Add the 2 gems bellow to your Gemfile then run bundle install:

gem 'carrierwave'
gem 'carrierwave-base64'

If you have trouble understanding how carrierwave is working behind the scenes watch File Uploading in Rails with Carrierwave.

Generate the file that will contain the configuration for carrierwave:

rails generate uploader Cover

After configuring app/uploaders/cover_uploader.rb we need to add the cover column to the books table.

rails generate migration AddCoverToBook cover:string

If you try to run rails console and end up with an uninitialized constant error, add the lines bellow to your config/application.rb:

require 'carrierwave'
require 'carrierwave/orm/activerecord'