Flash messages in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

How does the flash behave after a redirect in Rails?

Consider a Rails controller action that sets flash[:notice] = 'Saved!' and then redirects to another action. What will the user see on the redirected page if it displays flash[:notice]?

A The message 'Saved!' will be displayed only if the redirected page sets <code>flash.now[:notice]</code>.

B The message 'Saved!' will be displayed repeatedly on every page until the session ends.

C The message 'Saved!' will not be displayed on the redirected page.

D The message 'Saved!' will be displayed once on the redirected page.

💡 Hint

Think about how flash messages persist only for one request after a redirect.

Flash messages in Rails are designed to persist for exactly one request, typically after a redirect. Setting flash[:notice] before a redirect makes the message available on the next page load, then it disappears.

📝 Syntax

intermediate

Which code correctly sets a flash message that appears only on the current page?

You want to show a flash message that appears immediately on the current page without redirecting. Which code snippet correctly does this in a Rails controller?

A flash[:alert] = 'Error occurred'; render :edit

B flash[:alert] = 'Error occurred'; redirect_to edit_path

C flash.now[:alert] = 'Error occurred'; render :edit

D flash.now[:alert] = 'Error occurred'; redirect_to edit_path

💡 Hint

Use flash.now when rendering without redirecting.

flash.now sets a flash message that is available only for the current request, which is useful when rendering a template without redirecting.

🔧 Debug

advanced

Why does this flash message not appear after redirect?

Given this controller code:

def create
  flash.now[:notice] = 'Created successfully'
  redirect_to root_path
end

Why will the flash message not appear on the redirected page?

Ruby on Rails

def create
  flash.now[:notice] = 'Created successfully'
  redirect_to root_path
end

A <code>flash.now</code> messages do not persist across redirects, so the message is lost.

B <code>redirect_to</code> clears all flash messages before redirecting.

C The flash message key should be <code>:alert</code> instead of <code>:notice</code>.

D The message will appear only if the redirected page explicitly calls <code>flash.keep</code>.

💡 Hint

Remember the difference between flash and flash.now.

flash.now is for messages that appear only on the current request, usually when rendering. It does not persist through redirects, so the message disappears.

❓ state_output

advanced

What is the content of flash after multiple redirects?

Consider this sequence in a Rails controller:

flash[:info] = 'Step 1'
redirect_to step_two_path

# In step_two action:
flash[:info] = 'Step 2'
redirect_to step_three_path

# In step_three action:
# What is flash[:info]?

Ruby on Rails

flash[:info] = 'Step 1'
redirect_to step_two_path

# step_two action
flash[:info] = 'Step 2'
redirect_to step_three_path

# step_three action
flash[:info]

A 'Step 1'

B 'Step 2'

C nil

D An error is raised because flash is reset after each redirect

💡 Hint

Each redirect sets a new flash message that overwrites the previous one.

Flash messages set before a redirect persist to the next request. Setting flash[:info] again before the second redirect overwrites the first message. So on the third action, flash[:info] is 'Step 2'.

🧠 Conceptual

expert

Why should flash messages not be used for sensitive data?

Flash messages in Rails are stored in the session and displayed to users. Why is it a bad idea to store sensitive information (like passwords or personal data) in flash messages?

A Flash messages are stored in cookies or session and can be exposed to users or logged, risking data leaks.

B Flash messages automatically encrypt sensitive data, so storing sensitive info is safe.

C Flash messages are deleted immediately and never reach the user, so sensitive data is safe.

D Flash messages are only visible to admins, so sensitive data is protected.

💡 Hint

Think about where flash data is stored and who can access it.

Flash messages are stored in the session or cookies and sent to the user's browser. Sensitive data stored there can be exposed to users or appear in logs, so it should never be stored in flash.