API-only application setup in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a new Rails API-only application.

Ruby on Rails

rails new my_api_app --[1]

Drag options to blanks, or click blank then click option'

Aminimal

Bapi

Cfull

Dweb

Attempts:

3 left

💡 Hint

Common Mistakes

Using --full creates a full Rails app with views and assets.

Using --minimal is not a valid Rails new flag.

Using --web is not a recognized option.

Using --api creates a Rails application optimized for API-only use.

2fill in blank

medium

Complete the code to generate a controller in an API-only Rails app.

Ruby on Rails

rails generate controller [1] --no-helper --no-assets

Drag options to blanks, or click blank then click option'

AHome

BAssets

CViews

DLayouts

Attempts:

3 left

💡 Hint

Common Mistakes

Generating controllers named 'Views' or 'Assets' which are not controllers.

Forgetting to skip helpers and assets in API apps.

Controllers in API apps handle JSON requests; helpers and assets are usually not needed.

3fill in blank

hard

Fix the error in the config to enable CORS in an API-only Rails app.

Ruby on Rails

Rails.application.config.middleware.insert_before 0, Rack::Cors do
  allow do
    origins '[1]'
    resource '*', headers: :any, methods: [:get, :post, :options]
  end
end

Drag options to blanks, or click blank then click option'

Anil

Blocalhost

Cexample.com

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'nil' causes errors.

Using 'localhost' restricts access to local only.

Using a domain without quotes causes syntax errors.

Using '*' allows all origins to access the API, which is common in development.

4fill in blank

hard

Fill both blanks to configure the API-only app to skip session and cookies middleware.

Ruby on Rails

config.api_only = true
config.middleware.delete [1]
config.middleware.delete [2]

Drag options to blanks, or click blank then click option'

AActionDispatch::Session::CookieStore

BActionDispatch::Cookies

CRack::Runtime

DActionDispatch::Flash

Attempts:

3 left

💡 Hint

Common Mistakes

Deleting unrelated middleware like Rack::Runtime.

Forgetting to delete cookies middleware.

API-only apps usually remove session and cookies middleware to keep the app lightweight.

5fill in blank

hard

Fill all three blanks to create a JSON response in a Rails API controller action.

Ruby on Rails

def index
  @items = Item.all
  render json: [1], status: [2], [3]: 'items'
end

Drag options to blanks, or click blank then click option'

A@items

B:ok

Croot

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of a variable for JSON data.

Using wrong status symbols.

Misnaming the root key option.

This renders the @items collection as JSON with HTTP status 200 and sets the root key to 'items'.

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