MVC architecture in Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Rails controller action render?

Given the following Rails controller action, what will be the rendered output when a user visits the corresponding route?

Ruby on Rails

class BooksController < ApplicationController
  def show
    @book = Book.find(params[:id])
  end
end

A It renders a JSON response of the @book object automatically.

B It renders the show.html.erb view with access to @book instance variable.

C It redirects to the index action of BooksController.

D It raises an error because no render or redirect is specified.

💡 Hint

In Rails, if no explicit render or redirect is called, it renders the view matching the action name.

Rails by default renders the view template that matches the controller action name unless told otherwise. Here, the show action will render show.html.erb and the instance variable @book is available in the view.

❓ state_output

intermediate

What is the value of @posts after this Rails model query?

Consider the following code in a Rails controller. What will be the value of @posts?

Ruby on Rails

class PostsController < ApplicationController
  def index
    @posts = Post.where(published: true).order(created_at: :desc).limit(5)
  end
end

A @posts contains posts ordered by title alphabetically.

B @posts contains all posts regardless of published status.

C @posts contains 5 random posts from the database.

D @posts contains the 5 most recently created posts where published is true.

💡 Hint

Look at the where, order, and limit methods chaining.

The query filters posts with published: true, orders them by newest first, and limits the result to 5 posts.

📝 Syntax

advanced

Which option correctly defines a Rails model with a validation?

Which of the following code snippets correctly defines a Rails model with a presence validation on the title attribute?

A

class Article < ApplicationRecord
  validates :title, presence: true
end

B

class Article < ApplicationRecord
  validates :title, presence
end

C

class Article < ApplicationRecord
  validates_presence_of :title
end

D

class Article < ApplicationRecord
  validate :title, presence: true
end

💡 Hint

Check the correct method name and syntax for validations.

Option A uses the correct validates method with the presence: true option. Option A uses an invalid method validate with wrong arguments. Option A uses deprecated syntax but still valid in older Rails versions. Option A misses the true value for presence.

❓ lifecycle

advanced

What happens when a Rails model callback before_save raises an exception?

If a before_save callback in a Rails model raises an exception, what is the effect on the save operation?

A The save operation is aborted and the exception propagates up, preventing the record from saving.

B The save operation ignores the exception and continues saving the record.

C The save operation retries the callback automatically before saving.

D The save operation saves the record but logs the exception silently.

💡 Hint

Callbacks can halt the save process if they raise errors.

Raising an exception in a before_save callback stops the save process and the exception is raised to the caller. The record is not saved.

🔧 Debug

expert

Why does this Rails view raise a 'undefined method' error for @user.name?

Given this view code snippet, why does it raise an error 'undefined method `name` for nil:NilClass'?

Ruby on Rails

<%= @user.name %>

A @user is set but the name method is missing in the User model.

B The view syntax is incorrect; it should be <%= user.name %> without @.

C @user is nil because the controller did not set @user before rendering the view.

D The error is caused by a missing database migration for the name column.

💡 Hint

Check if the instance variable is assigned in the controller.

The error means @user is nil, so calling name on nil fails. This usually happens if the controller forgets to assign @user.