First Rails application - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Rails controller action render?

Consider this Rails controller code. What will the browser display when visiting the index action?

Ruby on Rails

class ArticlesController < ApplicationController
  def index
    @articles = ['Ruby', 'Rails', 'MVC']
  end
end

A A plain page showing the list: Ruby, Rails, MVC

B A JSON response with the articles array

C A blank page because no view template is provided

D An error because there is no explicit render call

💡 Hint

Rails automatically renders a view matching the action name if no render call is given.

Rails by default renders the view template matching the controller action name. Here, index will render app/views/articles/index.html.erb which can use @articles to display the list.

📝 Syntax

intermediate

Identify the syntax error in this Rails route definition

Which option correctly fixes the syntax error in this routes file snippet?

Ruby on Rails

Rails.application.routes.draw do
  get 'welcome/index'
  root to: 'welcome#index'
  resources :articles
  get 'articles/show/:id' => 'articles#show'
end

A Replace <code>root to: 'welcome#index'</code> with <code>root 'welcome#index'</code>

B Add a comma after <code>resources :articles</code>

C Change <code>get 'articles/show/:id' => 'articles#show'</code> to <code>get 'articles/:id' => 'articles#show'</code>

D Remove the <code>get 'welcome/index'</code> line

💡 Hint

Check the URL pattern for the show action in RESTful routes.

The route get 'articles/show/:id' is not a standard RESTful pattern and may cause confusion. The correct pattern is get 'articles/:id' which matches the show action properly.

❓ state_output

advanced

What is the output of this Rails view code?

Given the controller sets @name = 'Alice', what will this ERB template output?

Ruby on Rails

<h1>Welcome, <%= @name.upcase %>!</h1>
<p>Today is <%= Date.today.strftime('%A') %>.</p>

A <h1>Welcome, ALICE!</h1><p>Today is Monday.</p>

B <h1>Welcome, Alice!</h1><p>Today is Monday.</p>

C <h1>Welcome, ALICE!</h1><p>Today is <%= Date.today.strftime('%A') %>.</p>

D An error because <code>Date</code> is not available in views

💡 Hint

ERB evaluates Ruby code inside <%= %> and Date is accessible in views.

The @name.upcase converts 'Alice' to 'ALICE'. The Date.today.strftime('%A') outputs the current weekday name, e.g., 'Monday'.

🔧 Debug

advanced

Why does this Rails form not submit data?

This form in a Rails view does not send data to the controller. What is the cause?

Ruby on Rails

<%= form_with url: articles_path, method: :post do %>
  <%= text_field_tag :title %>
  <%= submit_tag 'Create' %>
<% end %>

A The form block is missing a variable for the form builder

B The form_with helper uses remote: true by default, so no page reload occurs

C The text_field_tag is not inside the form block properly

D The form_with helper requires a model object to submit data

💡 Hint

Check the default behavior of form_with regarding remote submission.

By default, form_with submits data via AJAX (remote: true), so the page does not reload. If the controller does not handle AJAX, it may seem like the form does nothing.

🧠 Conceptual

expert

What is the role of the ApplicationController in a Rails app?

Choose the best description of ApplicationController in a Rails application.

A It defines the routes and URL mappings for the application

B It handles database connections and queries for all models

C It is the main view template that all pages render by default

D It is the base controller that other controllers inherit from, sharing common behavior and filters

💡 Hint

Think about inheritance and shared code in controllers.

ApplicationController is the parent class for all controllers in Rails. It allows sharing methods, filters, and behavior across controllers.

Practice

1. What command do you use to create a new Rails application folder?

easy

A. rails init myapp

B. rails new myapp

C. rails create myapp

D. rails start myapp

Solution

1. Step 1: Understand Rails app creation command

   The official command to create a new Rails app is rails new followed by the app name.

2. Step 2: Match the command with options

   Only rails new myapp uses rails new myapp, which is correct syntax.

3. Final Answer:

   rails new myapp -> Option B

4. Quick Check:

   Create app folder = rails new [OK]

Hint: Remember: 'rails new' creates the app folder [OK]

Common Mistakes:

• Using 'rails start' instead of 'rails new'
• Confusing 'rails create' with 'rails new'
• Trying 'rails init' which is not a Rails command

2. Which command starts the Rails server so you can view your app in a browser?

easy

A. rails launch

B. rails start

C. rails run

D. rails server

Solution

1. Step 1: Identify the command to run the Rails server

   The correct command to start the Rails server is rails server.

2. Step 2: Compare with options

   Only rails server matches the correct command exactly.

3. Final Answer:

   rails server -> Option D

4. Quick Check:

   Start server = rails server [OK]

Hint: Use 'rails server' to launch your app locally [OK]

Common Mistakes:

• Typing 'rails start' which is invalid
• Using 'rails run' which does not start the server
• Trying 'rails launch' which is not a Rails command

3. What will happen if you run rails new blog and then cd blog followed by rails server?

medium

A. A new Rails app named 'blog' is created and the server starts to serve it locally.

B. An error occurs because 'rails server' must be run before 'rails new'.

C. The server starts but shows a blank page because no views are created yet.

D. The command fails because 'cd blog' is not a valid Rails command.

Solution

1. Step 1: Understand the sequence of commands

   rails new blog creates a new app folder named 'blog'. cd blog moves into that folder. rails server starts the server for that app.

2. Step 2: Analyze the expected behavior

   Running these commands in order creates the app and starts the server correctly, serving the default Rails welcome page.

3. Final Answer:

   A new Rails app named 'blog' is created and the server starts to serve it locally. -> Option A

4. Quick Check:

   rails new + cd + rails server = app runs [OK]

Hint: Create app, enter folder, then start server to see app [OK]

Common Mistakes:

• Thinking 'rails server' must run before app creation
• Assuming 'cd blog' is a Rails command instead of shell
• Expecting an error when running these commands in order

4. You ran rails new myapp but when you try rails server inside the folder, you get an error. What is the most likely cause?

medium

A. You must create a controller before starting the server.

B. You need to run rails start instead of rails server.

C. You forgot to run bundle install to install dependencies.

D. The folder name 'myapp' is invalid for Rails apps.

Solution

1. Step 1: Identify common setup step after creating app

   After rails new, you usually run bundle install to install gems needed by the app.

2. Step 2: Understand error cause

   If dependencies are missing, rails server will fail to start due to missing gems.

3. Final Answer:

   You forgot to run bundle install to install dependencies. -> Option C

4. Quick Check:

   Missing gems? Run bundle install first [OK]

Hint: Run 'bundle install' after 'rails new' before starting server [OK]

Common Mistakes:

• Trying 'rails start' which is invalid
• Thinking a controller is required before server start
• Believing folder name causes the error

5. You want to create a new Rails app named shop and immediately start the server. Which sequence of commands is correct?

hard

A. rails new shop -> cd shop -> rails server

B. rails create shop -> rails server

C. rails new shop -> rails server

D. cd shop -> rails new shop -> rails server

Solution

1. Step 1: Create the app folder with correct command

   Use rails new shop to create the app folder named 'shop'.

2. Step 2: Change directory into the new app folder

   Run cd shop to move into the app folder before starting the server.

3. Step 3: Start the Rails server inside the app folder

   Run rails server to launch the app locally.

4. Final Answer:

   rails new shop -> cd shop -> rails server -> Option A

5. Quick Check:

   Create app, enter folder, start server = correct order [OK]

Hint: Create app, cd into it, then run server [OK]

Common Mistakes:

• Skipping 'cd' before running server
• Using 'rails create' which is invalid
• Running server outside app folder