API-only application setup in Ruby on Rails - Mini Project: Build & Apply

API-only Application Setup with Rails

📖 Scenario: You are building a simple backend API for a to-do list app. The API will only send and receive JSON data without any HTML views.

🎯 Goal: Create a new Rails API-only application with a basic setup ready to build JSON endpoints.

📋 What You'll Learn

Create a new Rails application configured as API-only

Set the application name to todo_api

Configure the application to skip views, helpers, and assets

Add a simple controller to test the API setup

💡 Why This Matters

🌍 Real World

API-only Rails apps are used to build backend services that provide data to frontend apps or mobile apps via JSON.

💼 Career

Many companies build APIs with Rails to separate frontend and backend, making this skill valuable for backend and full-stack developer roles.

1

Create a new Rails API-only application

Run the command to create a new Rails application named todo_api with the --api option to make it API-only.

Ruby on Rails

# Run the command to create the Rails API-only app
# Your code here

Hint

Use rails new with the --api flag to create an API-only app.

2

Navigate into the application directory

Change directory into the newly created todo_api folder to start working inside the app.

Ruby on Rails

rails new todo_api --api
# Change directory into todo_api
# Your code here

Hint

Use cd todo_api to enter the app folder.

3

Generate a controller for testing the API

Generate a controller named todos with an action index to test the API setup. Use the Rails generator command.

Ruby on Rails

rails new todo_api --api
cd todo_api
# Generate todos controller with index action
# Your code here

Hint

Use rails generate controller todos index to create the controller and action.

4

Modify the todos controller to render JSON

Edit the TodosController to have the index action render a JSON response with a message { message: 'API is working' }.

Ruby on Rails

rails new todo_api --api
cd todo_api
rails generate controller todos index

# Edit app/controllers/todos_controller.rb
# Add JSON render in index action
# Your code here

Hint

In TodosController, define index to render json: { message: 'API is working' }.

Practice

1. What is the main purpose of creating a Rails application with the --api flag?

easy

A. To generate a full Rails app with HTML views and assets

B. To enable automatic frontend scaffolding

C. To create a lightweight backend that serves JSON responses only

D. To create a desktop application using Rails

Solution

1. Step 1: Understand the --api flag purpose

   The --api flag creates a Rails app optimized for API use, focusing on JSON responses without HTML views.

2. Step 2: Compare with full Rails app

   Full Rails apps include views and assets, but API-only apps skip these for lightweight backend.

3. Final Answer:

   To create a lightweight backend that serves JSON responses only -> Option C

4. Quick Check:

   API-only app = JSON backend [OK]

Hint: API-only means JSON backend, no HTML views [OK]

Common Mistakes:

• Thinking API-only apps generate HTML views
• Confusing API-only with full Rails app
• Assuming API-only creates frontend code

2. Which command correctly creates a new Rails API-only application named my_api?

easy

A. rails new my_api --full

B. rails new my_api --api

C. rails generate api my_api

D. rails create my_api --api-only

Solution

1. Step 1: Recall the Rails new command syntax

   The correct way to create an API-only app is using rails new app_name --api.

2. Step 2: Match the command with the app name

   Using rails new my_api --api matches the requirement exactly.

3. Final Answer:

   rails new my_api --api -> Option B

4. Quick Check:

   rails new + app name + --api = correct command [OK]

Hint: Use 'rails new app_name --api' to create API apps [OK]

Common Mistakes:

• Using --full instead of --api
• Using 'generate' instead of 'new'
• Incorrect flag like --api-only

3. Given this Rails API-only controller code, what will be the JSON response when accessing /api/greetings?

class Api::GreetingsController < ApplicationController
  def index
    render json: { message: 'Hello, API!' }
  end
end

medium

A. Redirect to root path

B. Hello, API!

C. Error: Missing view template

D. {"message":"Hello, API!"}

Solution

1. Step 1: Analyze the controller action

   The index action uses render json: to send a JSON response with a message.

2. Step 2: Understand API-only behavior

   API-only apps respond with JSON, so the output is the JSON string of the hash.

3. Final Answer:

   {"message":"Hello, API!"} -> Option D

4. Quick Check:

   render json = JSON output [OK]

Hint: render json sends JSON, not HTML [OK]

Common Mistakes:

• Expecting HTML output in API-only app
• Assuming missing view causes error
• Thinking it redirects automatically

4. You created a Rails API-only app but get an error: ActionController::UnknownFormat when requesting JSON. What is the likely cause?

medium

A. The controller action does not specify render json:

B. The app was created without the --api flag

C. The route is missing in routes.rb

D. The database is not migrated

Solution

1. Step 1: Understand the error meaning

   ActionController::UnknownFormat means the controller does not know how to respond to the requested format.

2. Step 2: Check controller response method

   If the action lacks render json:, Rails can't respond with JSON, causing this error.

3. Final Answer:

   The controller action does not specify render json: -> Option A

4. Quick Check:

   UnknownFormat = missing render json [OK]

Hint: Always use render json in API controllers [OK]

Common Mistakes:

• Assuming missing --api flag causes this error
• Thinking missing route causes UnknownFormat
• Blaming database migration for format errors

5. You want to add authentication to your Rails API-only app using token-based headers. Which setup step is essential to support this in an API-only app?

hard

A. Add middleware for session and cookies support manually

B. Generate views for login and logout pages

C. Use rails new without --api to enable sessions

D. Disable JSON responses to allow HTML forms

Solution

1. Step 1: Understand API-only app default middleware

   API-only apps exclude middleware for sessions and cookies by default to stay lightweight.

2. Step 2: Add middleware manually for token auth

   To support token-based authentication using headers, you often need session or cookie middleware added manually.

3. Final Answer:

   Add middleware for session and cookies support manually -> Option A

4. Quick Check:

   API-only needs manual middleware for sessions [OK]

Hint: Add session middleware manually for token auth [OK]

Common Mistakes:

• Expecting views for login in API-only app
• Recreating full app without --api flag
• Disabling JSON responses breaks API design