Action methods in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What does this Rails controller action render?

Consider this Rails controller action:

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

What will this action render by default when called?

A It renders the template 'show.html.erb' inside the 'users' folder automatically.

B It renders plain text with the user's name.

C It redirects to the index action of the controller.

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

💡 Hint

Rails automatically renders a view matching the action name unless told otherwise.

In Rails, if an action does not explicitly call render or redirect, it automatically renders the template matching the action name in the controller's view folder.

❓ state_output

intermediate

What is the value of @message after this action runs?

Given this Rails controller action:

def greet
  @message = params[:name] || 'Guest'
end

If the URL is '/greet?name=Alice', what is the value of @message?

A An error is raised because params[:name] is a string

B 'Alice'

C nil

D 'Guest'

💡 Hint

Check if params[:name] exists and what value it holds.

Since the URL provides 'name=Alice', params[:name] is 'Alice', so @message is set to 'Alice'.

📝 Syntax

advanced

Which option correctly defines a Rails action that redirects to root path?

You want an action named 'home' that redirects users to the root path. Which code is correct?

A

def home
  redirect root_path
end

B

def home
  render root_path
end

C

def home
  redirect_to root_path
end

D

def home
  redirect_to :root
end

💡 Hint

Look for the correct Rails method to redirect and the correct argument.

'redirect_to' is the correct method to redirect, and 'root_path' is the helper for the root URL.

🔧 Debug

advanced

Why does this action raise an error?

Examine this Rails controller action:

def update
  @post = Post.find(params[:id])
  @post.update(params[:post])
  redirect_to @post
end

Why might this code raise an error?

A params[:post] is not permitted, causing a ForbiddenAttributesError.

B Post.find(params[:id]) returns nil, causing a NoMethodError.

C redirect_to @post is invalid syntax and causes a syntax error.

D update method does not exist on ActiveRecord objects.

💡 Hint

Check how Rails handles strong parameters for mass assignment.

Rails requires strong parameters to permit attributes for update. Passing params[:post] directly causes a ForbiddenAttributesError.

🧠 Conceptual

expert

Which statement about Rails action methods is true?

Select the correct statement about action methods in Rails controllers.

A Action methods must always explicitly call render or redirect_to to produce a response.

B Private methods in controllers can be used as actions if called via routes.

C Action methods run only once when the server starts, then cache their output.

D Action methods can access params and instance variables to pass data to views.

💡 Hint

Think about how data flows from controller to view in Rails.

Action methods have access to params and can set instance variables that views use to display data.

Practice

1. What is the primary role of an action method in a Rails controller?

easy

A. To respond to user requests by processing data and rendering views or redirects

B. To define database schema and migrations

C. To style the HTML pages with CSS

D. To manage server configuration settings

Solution

1. Step 1: Understand the purpose of action methods

   Action methods in Rails controllers handle user requests by processing data and deciding what to show next.

2. Step 2: Differentiate from other roles

   Database schema, styling, and server settings are handled elsewhere, not in action methods.

3. Final Answer:

   To respond to user requests by processing data and rendering views or redirects -> Option A

4. Quick Check:

   Action methods handle requests = A [OK]

Hint: Action methods handle requests and responses in controllers [OK]

Common Mistakes:

• Confusing action methods with database migrations
• Thinking action methods style pages
• Assuming action methods configure servers

2. Which of the following is the correct syntax to define an action method named show in a Rails controller?

easy

A. function show() {}

B. def show; end

C. show() => {}

D. def show() {}

Solution

1. Step 1: Recall Ruby method syntax in Rails controllers

   Rails controller actions are Ruby methods defined with def method_name; end.

2. Step 2: Identify correct syntax

   def show; end uses correct Ruby syntax without parentheses, which is common in Rails.

3. Final Answer:

   def show; end -> Option B

4. Quick Check:

   Ruby method syntax = A [OK]

Hint: Rails actions use Ruby method syntax: def name; end [OK]

Common Mistakes:

• Using JavaScript function syntax
• Adding parentheses with braces in Ruby
• Mixing arrow functions with Ruby

3. Given this Rails controller action:

def index
  @users = User.all
end

What will @users contain after this action runs?

medium

A. A hash of user attributes

B. A single User record

C. An array of all User records from the database

D. An empty array

Solution

1. Step 1: Understand User.all in Rails

   User.all fetches all records from the users table as an ActiveRecord collection (like an array).

2. Step 2: Determine the content of @users

   It will contain all user records, not just one or empty or a hash.

3. Final Answer:

   An array of all User records from the database -> Option C

4. Quick Check:

   User.all returns all records = D [OK]

Hint: User.all fetches all records as a collection [OK]

Common Mistakes:

• Thinking User.all returns a single record
• Assuming it returns a hash
• Confusing with empty array if no users exist

4. Identify the error in this Rails controller action:

def create
  @user = User.new(params[:user])
  if @user.save
    redirect_to @user
  else
    render :new
  end
end

medium

A. Missing an end keyword

B. Using render instead of redirect_to in else

C. Redirecting to @user instead of a URL string

D. Using params[:user] directly without strong parameters

Solution

1. Step 1: Check parameter handling in create action

   Rails requires strong parameters to whitelist allowed attributes for security.

2. Step 2: Identify misuse of params[:user]

   Using params[:user] directly is unsafe and will cause an error in modern Rails.

3. Final Answer:

   Using params[:user] directly without strong parameters -> Option D

4. Quick Check:

   Strong parameters needed = B [OK]

Hint: Always use strong parameters for mass assignment [OK]

Common Mistakes:

• Ignoring strong parameters security
• Thinking redirect_to needs a URL string only
• Missing end keyword (not true here)

5. You want to add a custom action method publish to your PostsController that changes a post's status to 'published' and then redirects to the post's page. Which code snippet correctly implements this?

hard

A. def publish
@post = Post.find(params[:id])
@post.status = 'published'
@post.save
redirect_to post_path(@post)
end

B. def publish
@post = Post.find(params[:id])
@post.status = 'published'
redirect_to post_path(@post)
end

C. def publish
@post = Post.find(params[:id])
@post.status = 'published'
redirect_to @post
end

D. def publish
@post = Post.find(params[:id])
@post.save(status: 'published')
redirect_to @post
end

Solution

1. Step 1: Find the post by ID

   All options correctly find the post using Post.find(params[:id]).

2. Step 2: Update the post's status and save changes

   def publish @post = Post.find(params[:id]) @post.status = 'published' redirect_to @post end changes status but does not save. def publish @post = Post.find(params[:id]) @post.status = 'published' redirect_to post_path(@post) end changes status but does not save. def publish @post = Post.find(params[:id]) @post.status = 'published' @post.save redirect_to post_path(@post) end changes status, calls save, then redirects. def publish @post = Post.find(params[:id]) @post.save(status: 'published') redirect_to @post end incorrectly uses save(status: 'published') which is invalid.

3. Step 3: Redirect to the post's show page

   Options A, C, and D redirect correctly. def publish @post = Post.find(params[:id]) @post.status = 'published' redirect_to post_path(@post) end uses post_path(@post) which is also correct.

4. Final Answer:

   def publish @post = Post.find(params[:id]) @post.status = 'published' @post.save redirect_to post_path(@post) end -> Option A

5. Quick Check:

   Change attribute + save + redirect = C [OK]

Hint: Change attribute, save record, then redirect [OK]

Common Mistakes:

• Forgetting to save after changing attribute
• Using invalid save syntax with parameters
• Not redirecting after update