JSON rendering in Ruby on Rails - Mini Project: Build & Apply

JSON rendering

📖 Scenario: You are building a simple Rails API that returns user information in JSON format. This is common when creating backend services that frontend apps or other services consume.

🎯 Goal: Create a Rails controller action that renders a JSON response with user data.

📋 What You'll Learn

Create a hash with user data including id, name, and email

Set a status code variable for the HTTP response

Render the JSON response using the render json: method with the user data

Include the status code in the render call

💡 Why This Matters

🌍 Real World

APIs often send data as JSON to frontend apps or other services. Knowing how to render JSON in Rails is essential for backend development.

💼 Career

Backend developers frequently build JSON APIs. This skill is fundamental for roles involving Rails API development or full-stack development.

1

Create user data hash

Create a hash called user with these exact key-value pairs: id: 1, name: 'Alice', and email: '[e-mail]'.

Ruby on Rails

# Create a hash called user with id, name, and email
# Your code here

Hint

Use Ruby hash syntax with symbol keys and string values.

2

Set HTTP status code

Create a variable called status_code and set it to :ok to represent a successful HTTP response.

Ruby on Rails

user = { id: 1, name: 'Alice', email: '[e-mail]' }
# Create a variable status_code and set it to :ok
# Your code here

Hint

Use a symbol :ok for the status code.

3

Render JSON response

Use render json: user to render the user hash as JSON in the controller action.

Ruby on Rails

user = { id: 1, name: 'Alice', email: '[e-mail]' }
status_code = :ok
# Render the user hash as JSON
# Your code here

Hint

Use the render method with json: option.

4

Add status code to render call

Modify the render call to include the status: status_code option so the HTTP response uses the status_code variable.

Ruby on Rails

user = { id: 1, name: 'Alice', email: '[e-mail]' }
status_code = :ok
render json: user # Add status: status_code option here
# Your code here

Hint

Add status: status_code inside the render method call.

Practice

1. What does render json: @user do in a Rails controller?

easy

A. It sends the @user object as a JSON response to the client.

B. It renders an HTML view named 'json'.

C. It saves the @user object to the database in JSON format.

D. It redirects the user to a JSON page.

Solution

1. Step 1: Understand the render method with json option

   The render json: command in Rails sends data as JSON format to the client instead of rendering an HTML view.

2. Step 2: Identify the effect of @user in this context

   Passing @user sends the user object data as JSON in the HTTP response.

3. Final Answer:

   It sends the @user object as a JSON response to the client. -> Option A

4. Quick Check:

   render json: @user = send JSON response [OK]

Hint: render json: sends data as JSON response [OK]

Common Mistakes:

• Thinking it renders an HTML view named 'json'
• Confusing render json with saving data
• Assuming it redirects to another page

2. Which of the following is the correct syntax to render a JSON response with a status code 201 in Rails?

easy

A. render json: @post, code: 201

B. render json => @post, status = 201

C. render json: @post status 201

D. render json: @post, status: 201

Solution

1. Step 1: Identify correct Ruby hash syntax for render options

   In Rails, options are passed as key: value pairs separated by commas, e.g., json: @post, status: 201.

2. Step 2: Check each option for syntax correctness

   render json: @post, status: 201 uses correct Ruby hash syntax. Options B, C, and D have syntax errors or wrong keys.

3. Final Answer:

   render json: @post, status: 201 -> Option D

4. Quick Check:

   Correct Ruby hash syntax = render json: @post, status: 201 [OK]

Hint: Use commas and colons for options in render [OK]

Common Mistakes:

• Using => instead of : in Ruby 3+ syntax
• Missing commas between options
• Using wrong keys like code instead of status

3. Given the controller code:

def show
  @user = User.find(1)
  render json: @user.to_json(only: [:id, :name])
end

What will the JSON response include?

medium

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

B. {"name":"Alice"}

C. {"id":1}

D. {"id":1,"name":"Alice","email":"[e-mail]"}

Solution

1. Step 1: Understand the use of to_json(only: [:id, :name])

   This limits the JSON output to only the id and name fields of the user object.

2. Step 2: Identify which fields appear in the JSON response

   Only id and name are included, so email is excluded.

3. Final Answer:

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

4. Quick Check:

   only: [:id, :name] = id and name fields only [OK]

Hint: only: limits JSON fields included [OK]

Common Mistakes:

• Assuming all fields are included by default
• Confusing only: with except:
• Not calling to_json with options

4. What is wrong with this Rails controller code?

def index
  @users = User.all
  render json: @users only: [:id, :email]
end

medium

A. The @users variable should be a single user, not all users.

B. The only option should be inside to_json method, not passed directly to render.

C. You cannot render collections as JSON in Rails.

D. The render method requires a template name.

Solution

1. Step 1: Check how to limit JSON fields for collections

   The only option must be passed inside to_json or as a render json: option hash, not as a separate argument.

2. Step 2: Identify the correct way to pass only option

   Correct usage: render json: @users.to_json(only: [:id, :email]) or render json: @users, only: [:id, :email] inside a hash, but the given code passes only outside the hash.

3. Final Answer:

   The only option should be inside to_json method, not passed directly to render. -> Option B

4. Quick Check:

   only option must be inside to_json or render json hash [OK]

Hint: Pass only inside to_json or render json hash [OK]

Common Mistakes:

• Passing only as separate argument outside render hash
• Thinking collections can't be rendered as JSON
• Forgetting to call to_json with options

5. You want to render a JSON response with a list of users, but only include users with active status true and only their id and name fields. Which code correctly does this in a Rails controller?

hard

A. render json: User.where(active: true) only: [:id, :name]

B. render json: User.all.select(:id, :name).where(active true)

C. render json: User.where(active: true).to_json(only: [:id, :name])

D. render json: User.where(active: true).only(:id, :name)

Solution

1. Step 1: Filter users by active status

   Use User.where(active: true) to get only active users.

2. Step 2: Limit JSON fields to id and name

   Call to_json(only: [:id, :name]) to include only those fields in the JSON output.

3. Step 3: Check each option for correctness

   render json: User.where(active: true).to_json(only: [:id, :name]) correctly chains filtering and JSON field limiting. render json: User.all.select(:id, :name).where(active: true) has wrong method order and will error. render json: User.where(active: true), only: [:id, :name] passes only incorrectly. render json: User.where(active: true).only(:id, :name) uses a non-existent only method on ActiveRecord relation.

4. Final Answer:

   render json: User.where(active: true).to_json(only: [:id, :name]) -> Option C

5. Quick Check:

   Filter then to_json with only: fields [OK]

Hint: Filter first, then call to_json with only: [OK]

Common Mistakes:

• Using only as a method on ActiveRecord relation
• Passing only outside to_json or render json hash
• Selecting fields before filtering causing errors