Building a Ruby on Rails API

What is Ruby on Rails API?

Rails is a web-application framework that includes everything needed to create database-backed web applications according to the Model-View-Controller (MVC) pattern.

Understanding the MVC pattern is key to understanding Rails. MVC divides your application into three layers: Model, View, and Controller, each with a specific responsibility.

Creating Rails API

First, open a terminal application and run:

rails new our-api --api && cd our-api

By passing --api Rails will not generate any views in case we run a scaffold migration.

Now open our-api in a text editor or IDE of your choice and navigate to config/routes.rb to create our first route. Add the following:

Rails.application.routes.draw do
get 'api/vehicles', to: 'application#vehicles'

Now open app/controllers/application_controller.rb and paste the following code snippet:

class ApplicationController < ActionController::API
def vehicles
render json: { name: 'Tesla Model 3' }

At this point it’s worthwhile to test it out to make sure everything is set up correctly. To start the server simply run:

rails s

If the browser you’re using supports rendering JSON, just open http://localhost:3000/api/vehicles in your browser directly.

Alternatively, I recommend using Postman or Insomnia.

The response should be following:

"name": "Tesla Model 3"

Seed the database

In this exercise we’ll use SQLite for the database, this means it’s just a file within our project — it won’t require a server or host. Rails migrations can be run to actually interact with the DB.

In your terminal run the following:

rails g model Vehicle name:string price:decimal{10-2} picture:text

What does this do? It generates a model called Vehicle and 3 fields in the database: name, price and picture.

Now run the following:

rake db:migrate

Now open application_controller.rb and add the following:

class ApplicationController < ActionController::API
def vehicles
@vehicles = Vehicle.all
render json: @vehicles

If you hit the api/vehicles endpoint, is should return an empty array []. This is expected; no data exists in the database yet. To add data, open db/seeds.rb. You’ll see that there’s already some examples there, but we’ll need to delete these and add our own:

{ name: 'Tesla Model S', price: '51885.17', picture: '$MT337,$PPSW,$W40B,$IBB1&view=STUD_FRONT34&model=m3&size=1920&bkba_opt=2&version=v0028d202109300916&crop=0,0,0,0&version=v0028d202109300916' },
{ name: 'Tesla Model 3', price: '100990', picture: '$MTS10,$PPSW,$WS90,$IBE00&view=FRONT34&model=ms&size=1920&bkba_opt=2&version=v0028d202109300916&crop=0,0,0,0&version=v0028d202109300916' },
{ name: 'Tesla Model X', price: '120990', picture: '$MTX10,$PPSW,$WX00,$IBE00&view=FRONT34&model=mx&size=1920&bkba_opt=2&version=v0028d202109300916&crop=0,0,0,0&version=v0028d202109300916' },
{ name: 'Tesla Model Y', price: '65000', picture: '$MTY07,$PPSW,$WY19B,$INPB0&view=FRONT34&model=my&size=1920&bkba_opt=2&version=v0028d202109300916&crop=0,0,0,0&version=v0028d202109300916' }

You might notice the picture URLs are quite long, we’re actually using the static image assets from the Tesla website. Now we can seed the database. To do this, run:

rake db:seed

Now if you hit api/vehicles it should return the 4 entries.


It’s practical and foreseeable that you’ll want to add more API resources, say locations, events and services. In this scenario, the routes.rb file would look like this:

Rails.application.routes.draw do
get 'api/vehicles', to: 'application#vehicles'
get 'api/locations', to: 'application#locations'
get 'api/events', to: 'application#events'
get 'api/services', to: 'application#services'

You probably notice each endpoint is repetitively prefaced with api/. This can be refactored for simplicity and readability scoping the routes.

Rails.application.routes.draw do
scope :api do
get 'vehicles', to: 'application#vehicles'
get 'locations', to: 'application#locations'
get 'events', to: 'application#events'
get 'services', to: 'application#services'



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Luis Castillo

Luis Castillo

Software Engineer / Full-Stack Developer in Ruby, Ruby on Rails, JavaScript, ReactJS, Redux, SQL, HTML5, CSS3