How to Build a Basic JSON API

Learning update!

During Module 3, we have been focusing on DOM manipulation, promises (ex. fetch), async, and building Rails JSON APIs from scratch.

In the Module 3 project, I am making a review site with a backend and frontend, then connecting the two via fetch requests.

So, I am going to walk through how to make most of the backend JSON API for this project with Rails!

Here is the overarching details for the total project:


- Must be a Single Page Application (SPA)


  • A property has many reviews
  • A property has a name, description, phone number, address, website
  • Each review belongs to a property
  • Each review has a title and content

User stories:

  • A user may create, read, update, and delete properties
  • A user may create, read, update, and delete reviews of properties
  • A user can view only 50 properties at a time and can click a button to view more properties
  • Stretch Goal: A user may search through properties using a filter that actively updates based on typing into a search box.
  • Stretch Goal: All properties are organized into cards that display 4x4 in a grid pattern on the page with photos using Semantic-UI

Let's start!

  1. Enter your CLI and run rails new yelp-api --database=postgresql --api -T to generate the application in the directory of your choice.

  2. cd into that directory

  3. check your gemfile and uncomment the gem rack-cors gem and add the gem active_model_serializers gem, also include gem 'faker' (for later) then run bundle install again. When done, continue to the next step.

  4. in config/initializers/cors.rb, uncomment the and edit the following to look like this:

Rails.application.config.middleware.insert_before 0, Rack::Cors do
  allow do
   origins '*'
    resource '*',
      headers: :any,
      methods: [:get, :post, :put, :patch, :delete, :options, :head]
  1. Next, let’s tackle routes. Head to the config/routes.rb file and namespace your routes for inclusion of ‘api’ and the version (‘v1’) like this:

    namespace :api do 
    namespace :v1 do 
        resources :properties
        resources :reviews
  2. Let’s make our controllers. Run rails g controller api/v1/Properties and rails g controller api/v1/Reviews in your CLI.

  3. Now, let’s head to the controllers in app/controllers/api/v1/.

You should see something like this in app/controllers/api/v1/properties_controller.rb

 class Api::V1::PropertiesController < ApplicationController

Let’s add some instructions for the controller in between the class declaration and the end. Like this:

 before_action :find_property, only: [:update]
  def index
    @property = Property.all
    render json: @property

  def update
      render json: @property, status: :accepted
      render json: { errors: @property.errors.full_messages }, status: :unprocessible_entity


  def property_params
    params.permit(:name, :description, :phone_number, :website, :address)

  def find_property
    @property = Property.find(params[:id])
  1. Do the same thing for reviews. Like this:
 before_action :find_review, only: [:update]
  def index
    @review = Review.all
    render json: @review

  def update
      render json: @review, status: :accepted
      render json: { errors: @review.errors.full_messages }, status: :unprocessible_entity


  def review_params
    params.permit(:title, :content)

  def find_review
    @review = Review.find(params[:id])
  1. Let’s create our models by running rails g model Property name description address phone_number website and rails g model Review title content in the CLI.

  2. Let’s run rails db:create && rails db:migrate to update and create our database in Postgres. Important: If you are not running the GUI Postgres, then the database will not run in your rails s command. You will get an error. So, please be sure to download Postgres first.

  3. Test out your database using rails c and then try Property.create(name: "McDonalds", ...) then run Property.all and it should appear! Do the same thing to test out reviews.

If you run rails s, then go to localhost:3000/api/v1/properties you will not see anything if you didn’t do Property.create(insert params here)! Let’s fix that with some seed data.

  1. Let’s use the faker gem we included in our gem file to create data for the backend database. Go to db/seeds.rb and type in the following:

    beachhouse = Property.create(name:, description:, address: Faker::Address.unique.street_address,phone_number: Faker::PhoneNumber.unique.cell_phone,website: Faker::Internet.unique.url)
    review = Review.create(title: "Five Guys Was Awesome", content: "Best french fries ever!") 
  2. run rake db:seed to migrate the data to the database.

  3. Now run rails s and navigate to your endpoint(localhost:3000/api/v1/properties or localhost:3000/api/v1/reviews). You can also check your routes using rails routes to see which routes work. You should see something like this for properties:

    id: 1,
    name: "Five Guys",
    description: "Good burger joint",
    address: "10001 Liberty Rd., Baltimore, MD, 21210",
    phone_number: "410-510-2390",
    website: "",
    created_at: "2018-05-29T19:00:32.364Z",
    updated_at: "2018-05-29T19:00:32.364Z"
    id: 2,
    name: "Alaina Bradtke",
    description: "target cutting-edge technologies",
    address: "268 Nikolaus Brooks",
    phone_number: "696.501.1132",
    website: "",
    created_at: "2018-05-29T19:11:44.965Z",
    updated_at: "2018-05-29T19:11:44.965Z"

This is great! That’s our JSON data that we get by sending a GET request to our API! It’s working!

Hint: If you want to see something prettier, feel free to download the JSONView extension for Chrome or something similar for your own browser. This will help you view JSON data easier and prettier!

  1. If you want to continue building out the project, you will need to build the relationship working between reviews and properties, as well as make specific configurations for the PostSerializer.

That’s it! Now, you have most of the backend JSON API for a review site! You can make fetch requests to it in the JS in the front-end, while the rails server is running.

Congratulations! You're done!

Published 30 May 2018

founder && full stack && ethereum developer.
Max Goodman on Twitter