Why Rails API mode exists - Test Your Understanding

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'

Afull

Bminimal

Capi

Dweb

Attempts:

3 left

💡 Hint

Common Mistakes

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

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

Using --minimal is not a recognized option.

The --api flag creates a Rails application optimized for APIs by excluding views and assets.

2fill in blank

medium

Complete the sentence explaining why Rails API mode excludes some features.

Ruby on Rails

Rails API mode excludes [1] and assets to make the app smaller and faster.

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

Aviews

Bmigrations

Ccontrollers

Dmodels

Attempts:

3 left

💡 Hint

Common Mistakes

Thinking models are excluded, but models are still used.

Controllers are still needed to handle requests.

Migrations are part of database setup and not excluded.

Rails API mode excludes views and assets because APIs usually send data, not HTML pages.

3fill in blank

hard

Fix the error in this Rails API controller method to respond with JSON.

Ruby on Rails

def show
  user = User.find(params[:id])
  render [1]: user
end

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

Atext

Bhtml

Cxml

Djson

Attempts:

3 left

💡 Hint

Common Mistakes

Using html renders a web page, not JSON data.

Using text or xml is not standard for Rails APIs.

In API mode, responses are usually JSON, so render json: user sends user data as JSON.

4fill in blank

hard

Fill both blanks to configure middleware for a Rails API app.

Ruby on Rails

class Application < Rails::Application
  config.api_only = [1]
  config.middleware.use [2]
end

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

Atrue

Bfalse

CActionDispatch::Cookies

DActionDispatch::Static

Attempts:

3 left

💡 Hint

Common Mistakes

Setting api_only to false disables API mode.

Adding Static middleware is for serving files, not cookies.

Setting config.api_only = true enables API mode. Adding ActionDispatch::Cookies middleware allows cookie support if needed.

5fill in blank

hard

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

Ruby on Rails

class GreetingsController < ApplicationController
  def hello
    message = { [1]: [2] }
    render [3]: message
  end
end

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

Agreeting

B"Hello, world!"

Cjson

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using text instead of json in render.

Forgetting to quote the string value.

Using an unrelated key name.

The hash key is greeting, the value is the string "Hello, world!", and render json: message sends JSON response.

Practice

1. Why does Rails provide an API mode when creating a new application?

easy

A. To build lightweight backends that only send data without views or assets

B. To create full web pages with embedded Ruby templates

C. To automatically generate frontend JavaScript code

D. To enable real-time chat features by default

Solution

1. Step 1: Understand Rails API mode purpose

   Rails API mode is designed to skip views, assets, and frontend parts to make the app lightweight.

2. Step 2: Compare options with this purpose

   Only To build lightweight backends that only send data without views or assets describes building a backend that sends data without views or assets, matching API mode's goal.

3. Final Answer:

   To build lightweight backends that only send data without views or assets -> Option A

4. Quick Check:

   Rails API mode = lightweight data-only backend [OK]

Hint: API mode skips views/assets for data-only backends [OK]

Common Mistakes:

• Thinking API mode generates frontend code
• Confusing API mode with full Rails apps with views
• Assuming API mode enables real-time features by default

2. Which command correctly creates a new Rails app in API mode?

easy

A. rails generate api myapp

B. rails new myapp --skip-api

C. rails new myapp --api

D. rails api new myapp

Solution

1. Step 1: Recall Rails app creation syntax

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

2. Step 2: Check each option

   rails new myapp --api uses 'rails new myapp --api' which is the correct syntax. Others are invalid commands.

3. Final Answer:

   rails new myapp --api -> Option C

4. Quick Check:

   rails new with --api flag = API mode app [OK]

Hint: Use --api flag with rails new to create API mode [OK]

Common Mistakes:

• Using 'rails generate api' which is not a valid command
• Trying to skip API mode with --skip-api which doesn't exist
• Using 'rails api new' which is invalid syntax

3. Given this Rails API controller code, what will be the JSON response when accessing /api/users/1?

class Api::UsersController < ApplicationController
  def show
    user = User.find(params[:id])
    render json: { id: user.id, name: user.name }
  end
end

medium

A. {"user":{"id":1,"name":"Alice"}}

B. User 1: Alice

C. Error: Missing template users/show

D. {"id":1,"name":"Alice"}

Solution

1. Step 1: Analyze controller render call

   The controller uses 'render json:' with a hash containing id and name keys, so it returns JSON with those keys at root.

2. Step 2: Match options with expected JSON

   {"id":1,"name":"Alice"} matches the JSON object with id and name keys directly. {"user":{"id":1,"name":"Alice"}} nests them inside 'user' key, which is not in code.

3. Final Answer:

   {"id":1,"name":"Alice"} -> Option D

4. Quick Check:

   render json: {id, name} = flat JSON object [OK]

Hint: render json: hash returns flat JSON, not HTML or nested by default [OK]

Common Mistakes:

• Expecting HTML response instead of JSON
• Assuming JSON keys are nested under 'user' automatically
• Thinking missing template error occurs in API mode

4. You created a Rails API app but get this error when calling an endpoint: ActionController::UnknownFormat. What is the likely cause?

medium

A. The controller action is trying to render HTML but API mode expects JSON

B. The database connection is missing

C. The routes file is empty

D. The API mode flag was not used during app creation

Solution

1. Step 1: Understand UnknownFormat error meaning

   This error happens when the controller tries to respond with a format not supported, often HTML in API mode.

2. Step 2: Match cause with options

   The controller action is trying to render HTML but API mode expects JSON correctly identifies that rendering HTML in API mode causes this error because API mode expects JSON responses.

3. Final Answer:

   The controller action is trying to render HTML but API mode expects JSON -> Option A

4. Quick Check:

   UnknownFormat = wrong response format in API mode [OK]

Hint: UnknownFormat means controller expects JSON, got HTML instead [OK]

Common Mistakes:

• Blaming database or routes for format errors
• Assuming API mode flag missing causes this error
• Ignoring response format mismatch

5. You want to build a backend for a mobile app using Rails API mode. Which of these is NOT a benefit of using API mode for this purpose?

hard

A. Faster response times by skipping view rendering

B. Automatic generation of mobile UI components

C. Smaller app size by excluding assets and helpers

D. Easier integration with frontend frameworks like React or Vue

Solution

1. Step 1: Review benefits of Rails API mode

   API mode skips views/assets for faster, smaller backend apps and works well with frontend frameworks.

2. Step 2: Identify which option is NOT a benefit

   Automatic generation of mobile UI components claims automatic mobile UI generation, which Rails API mode does not provide since it only handles backend data.

3. Final Answer:

   Automatic generation of mobile UI components -> Option B

4. Quick Check:

   API mode = backend only, no UI generation [OK]

Hint: API mode builds backend only; UI generation is separate [OK]

Common Mistakes:

• Thinking API mode creates frontend UI automatically
• Confusing smaller app size with missing features
• Assuming API mode limits frontend integration