MVC architecture in Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a Rails controller named PostsController.

Ruby on Rails

class PostsController < [1]
  def index
    @posts = Post.all
  end
end

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

AApplicationRecord

BApplicationController

CActiveRecord::Base

DActionController::Base

Attempts:

3 left

💡 Hint

Common Mistakes

Using ApplicationRecord which is for models.

Using ActiveRecord::Base which is for models.

Using ActionController::Base directly instead of ApplicationController.

The controller in Rails inherits from ApplicationController to handle web requests.

2fill in blank

medium

Complete the code to define a model named Post that inherits from the correct Rails class.

Ruby on Rails

class Post < [1]
  validates :title, presence: true
end

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

AApplicationRecord

BActiveRecord::Base

CApplicationController

DActionController::Base

Attempts:

3 left

💡 Hint

Common Mistakes

Using ApplicationController which is for controllers.

Using ActionController::Base which is for controllers.

Using ActiveRecord::Base directly instead of ApplicationRecord.

Models in Rails inherit from ApplicationRecord, which itself inherits from ActiveRecord::Base.

3fill in blank

hard

Fix the error in the view code to correctly display all post titles.

Ruby on Rails

<ul>
  <% @posts.[1] do |post| %>
    <li><%= post.title %></li>
  <% end %>
</ul>

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

Aselect

Bmap

Ceach

Dcollect

Attempts:

3 left

💡 Hint

Common Mistakes

Using map or collect which return new arrays but don't directly output.

Using select which filters but does not iterate all items.

In Rails views, each is used to loop through collections for display.

4fill in blank

hard

Fill both blanks to complete the route that maps GET requests for posts to the index action.

Ruby on Rails

Rails.application.routes.draw do
  [1] '[2]', to: 'posts#index'
end

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

Aget

Bpost

Cposts

Dindex

Attempts:

3 left

💡 Hint

Common Mistakes

Using post instead of get for a read route.

Using 'index' as the path instead of the resource name.

The get method defines a route for GET requests, and 'posts' is the URL path.

5fill in blank

hard

Fill all three blanks to complete a controller action that creates a new Post and redirects to its show page.

Ruby on Rails

def create
  @post = Post.new([1])
  if @post.[2]
    redirect_to [3], notice: 'Post was successfully created.'
  else
    render :new
  end
end

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

Apost_params

Bsave

C@post

Dupdate

Attempts:

3 left

💡 Hint

Common Mistakes

Using update instead of save in create action.

Redirecting to a path string instead of the post object.

Passing raw params instead of permitted parameters.

The post_params method provides safe parameters, save saves the record, and @post is used to redirect to the show page.

Practice

1. In the MVC architecture of Rails, which component is responsible for handling user input and controlling the flow of the application?

easy

A. Controller

B. Model

C. View

D. Router

Solution

1. Step 1: Understand MVC roles

   The Model manages data, the View displays data, and the Controller handles user input and application flow.

2. Step 2: Identify the component for user input

   The Controller receives user requests and decides what to do next.

3. Final Answer:

   Controller -> Option A

4. Quick Check:

   Controller = handles user input [OK]

Hint: Controller manages user actions and app flow [OK]

Common Mistakes:

• Confusing Model with Controller
• Thinking View handles user input
• Selecting Router as MVC component

2. Which of the following is the correct way to define a controller class in Rails?

easy

A. class UsersController inherits ApplicationController; end

B. def UsersController < ApplicationController; end

C. class UsersController < ApplicationController; end

D. controller UsersController extends ApplicationController {}

Solution

1. Step 1: Recall Ruby class syntax

   In Ruby, classes are defined with class ClassName < ParentClass and closed with end.

2. Step 2: Match Rails controller syntax

   Rails controllers inherit from ApplicationController using < syntax.

3. Final Answer:

   class UsersController < ApplicationController; end -> Option C

4. Quick Check:

   Ruby class syntax = class UsersController < ApplicationController; end [OK]

Hint: Use Ruby class inheritance syntax with < [OK]

Common Mistakes:

• Using 'def' instead of 'class'
• Using 'inherits' keyword (not Ruby)
• Using JavaScript-like syntax

3. Given the following Rails controller code, what will be the rendered output when visiting /welcome/index?

class WelcomeController < ApplicationController
  def index
    @message = "Hello, Rails!"
  end
end

And the view file app/views/welcome/index.html.erb contains:

<h1><%= @message %></h1>

medium

A. Hello, Rails!

B. @message

C. Error: undefined variable @message

D.

Solution

1. Step 1: Understand controller instance variable

   The controller sets @message to "Hello, Rails!" which is accessible in the view.

2. Step 2: Evaluate view rendering

   The view uses ERB tag <%= @message %> to insert the string value inside the <h1> tag.

3. Final Answer:

   <h1>Hello, Rails!</h1> -> Option A

4. Quick Check:

   Instance variable passed to view = <h1>Hello, Rails!</h1> [OK]

Hint: Instance variables in controller show in views with <%= %> [OK]

Common Mistakes:

• Using local variables instead of instance variables
• Forgetting = in ERB tag
• Expecting variable name printed literally

4. Identify the error in this Rails controller code snippet:

class ProductsController < ApplicationController
  def show
    @product = Product.find(params[:id])
  end

  def index
    @products = Product.all
  end
end

What is the likely cause of a runtime error when visiting /products/show without an id parameter?

medium

A. Method index should be defined before show

B. Missing id in params causes find to raise an exception

C. Instance variables cannot be used in controllers

D. Controller class name should be ProductController not ProductsController

Solution

1. Step 1: Analyze show method usage

   The show method calls Product.find(params[:id]), which requires a valid id parameter.

2. Step 2: Understand missing parameter effect

   If params[:id] is missing, find raises an ActiveRecord::RecordNotFound error causing a runtime failure.

3. Final Answer:

   Missing id in params causes find to raise an exception -> Option B

4. Quick Check:

   Missing param causes error = Missing id in params causes find to raise an exception [OK]

Hint: Always check required params before calling find [OK]

Common Mistakes:

• Thinking method order matters
• Believing instance variables are invalid
• Confusing singular/plural controller names

5. You want to display a list of all users with their email addresses in a Rails app. Which MVC components should you update and how? A) Update the Model to fetch users, Controller to assign users to a variable, and View to loop and display emails. B) Update only the View to query the database and display emails. C) Update the Controller to fetch users and display emails directly without a View. D) Update the Model to display emails and Controller to fetch users.

hard

A. Update Model to display and Controller to fetch

B. Update View only to query and display

C. Update Controller only to fetch and display

D. Update Model to fetch, Controller to assign, View to display

Solution

1. Step 1: Understand MVC responsibilities

   The Model handles data fetching, the Controller prepares data for the View, and the View displays data.

2. Step 2: Apply MVC to user list display

   The Model fetches users, Controller assigns them to an instance variable, and View loops through to show emails.

3. Final Answer:

   Update Model to fetch, Controller to assign, View to display -> Option D

4. Quick Check:

   MVC separation = Update Model to fetch, Controller to assign, View to display [OK]

Hint: Model fetches, Controller assigns, View displays [OK]

Common Mistakes:

• Putting database queries in the View
• Displaying data directly in Controller
• Making Model handle display logic