Flash messages in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set a flash message in a Rails controller.

Ruby on Rails

flash[:notice] = [1]

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

Arender

Bredirect_to

C:alert

D"Welcome!"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a symbol instead of a string for the message

Trying to call redirect_to instead of setting flash

Using render instead of setting flash

The flash message is set by assigning a string to flash[:notice]. Here, "Welcome!" is the message shown to the user.

2fill in blank

medium

Complete the code to redirect to the home page after setting a flash message.

Ruby on Rails

flash[:alert] = "Access denied"
[1] root_path

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

Aredirect_to

Brender

Cflash.now

Dlink_to

Attempts:

3 left

💡 Hint

Common Mistakes

Using render instead of redirect_to after setting flash

Using flash.now which does not persist after redirect

Using link_to which is for views, not controllers

After setting a flash message, you use redirect_to to send the user to another page, here root_path.

3fill in blank

hard

Fix the error in the code to display a flash message in the view.

Ruby on Rails

<% if flash[:[1]] %>
  <p><%= flash[:notice] %></p>
<% end %>

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

Anotice

Balert

Cmessage

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for flash[:alert] but displaying flash[:notice]

Using a key that was never set in flash

Not wrapping flash display in an if condition

The condition should check flash[:notice] to match the message displayed inside the paragraph.

4fill in blank

hard

Fill both blanks to create a flash message hash with keys and values.

Ruby on Rails

flash = { [1]: "Success!", [2]: "Error occurred" }

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

A:notice

B"notice"

C:alert

D"alert"

Attempts:

3 left

💡 Hint

Common Mistakes

Using strings instead of symbols for flash keys

Mixing symbols and strings inconsistently

Using keys that are not standard flash keys

Flash keys are symbols like :notice and :alert. Strings like "notice" won't work as expected.

5fill in blank

hard

Fill all three blanks to set a flash message, redirect, and display it in the view.

Ruby on Rails

class UsersController < ApplicationController
  def create
    if @user.save
      flash[[1]] = "User created"
      [2] users_path
    else
      flash.now[[3]] = "Error saving user"
      render :new
    end
  end
end

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

A:notice

Bredirect_to

C:alert

Drender

Attempts:

3 left

💡 Hint

Common Mistakes

Using flash.now for success messages that redirect

Using redirect_to after render

Mixing up :notice and :alert keys

Use flash[:notice] for success messages and flash.now[:alert] for errors shown on the same page. Use redirect_to to go to another page after success.

Practice

1. What is the main purpose of flash messages in a Rails application?

easy

A. To show temporary messages to users after actions like form submissions

B. To permanently store user data in the session

C. To style the webpage with CSS dynamically

D. To handle database transactions automatically

Solution

1. Step 1: Understand flash message role

   Flash messages provide feedback to users about actions they performed, like success or error notices.

2. Step 2: Differentiate from other features

   They are temporary and do not store data permanently or affect styling or database transactions.

3. Final Answer:

   To show temporary messages to users after actions like form submissions -> Option A

4. Quick Check:

   Flash messages = temporary user feedback [OK]

Hint: Flash messages show quick feedback after user actions [OK]

Common Mistakes:

• Thinking flash stores data permanently
• Confusing flash with CSS or styling
• Assuming flash manages database

2. Which of the following is the correct way to set a flash notice in a Rails controller?

easy

A. flash.notice = "Saved successfully"

B. flash->notice = "Saved successfully"

C. flash[:notice] = "Saved successfully"

D. flash('notice') = "Saved successfully"

Solution

1. Step 1: Recall flash syntax in Rails

   Flash messages are set using the hash-like syntax with symbols, e.g., flash[:notice] = "message".

2. Step 2: Identify correct syntax

   Options A, B, and C use invalid Ruby or Rails syntax for flash assignment.

3. Final Answer:

   flash[:notice] = "Saved successfully" -> Option C

4. Quick Check:

   flash[:key] = message [OK]

Hint: Use flash[:notice] = "message" to set flash [OK]

Common Mistakes:

• Using dot notation instead of brackets
• Using parentheses incorrectly
• Using arrow syntax which is invalid

3. Given this controller code snippet:

def create
  if @post.save
    flash[:notice] = "Post created!"
    redirect_to posts_path
  else
    flash[:alert] = "Error creating post"
    render :new
  end
end

What will happen to the flash messages if the post fails to save?

medium

A. The notice message will be shown on the posts index page

B. The alert message will be shown on the new post form page

C. No flash message will be shown because render does not keep flash

D. Both notice and alert messages will be shown on the new page

Solution

1. Step 1: Understand flash behavior with redirect and render

   Flash messages persist for one request. Redirect clears flash after showing it. Render keeps the current request, so flash remains.

2. Step 2: Analyze code flow on failure

   On failure, flash[:alert] is set and render :new is called, so alert message shows on the new form page.

3. Final Answer:

   The alert message will be shown on the new post form page -> Option B

4. Quick Check:

   flash with render = message shown immediately [OK]

Hint: Flash with render shows message immediately; with redirect, next page [OK]

Common Mistakes:

• Assuming flash clears on render
• Thinking notice shows on failure
• Confusing redirect and render flash behavior

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

def update
  if @user.update(user_params)
    flash[:notice] = "Profile updated"
    render redirect_to profile_path
  else
    flash[:alert] = "Update failed"
    redirect_to edit_profile_path
  end
end

medium

A. Using render with redirect_to together is incorrect syntax

B. flash[:notice] should be flash.notice

C. redirect_to cannot be used inside an if statement

D. flash messages must be set after redirect_to

Solution

1. Step 1: Check render and redirect usage

   In Rails, render and redirect_to are separate methods. You cannot combine them like render redirect_to.

2. Step 2: Identify correct usage

   To redirect, use redirect_to path. To render a template, use render :template_name. Mixing both causes syntax error.

3. Final Answer:

   Using render with redirect_to together is incorrect syntax -> Option A

4. Quick Check:

   render and redirect_to are separate calls [OK]

Hint: Use either render or redirect_to, never both together [OK]

Common Mistakes:

• Combining render and redirect_to
• Using dot notation for flash
• Setting flash after redirect instead of before

5. You want to show a flash message that persists for the current and the next request (for example, after a redirect and then another page load). Which method should you use in Rails?

hard

A. Use flash.now to set the message

B. Use flash.delete to save the message

C. Use flash.clear to keep the message

D. Use flash.keep to preserve the flash for another request

Solution

1. Step 1: Understand flash persistence

   By default, flash messages last for one request. flash.now shows message only for current request.

2. Step 2: Use flash.keep to extend flash life

   flash.keep preserves the flash message for an additional request, so it appears again after redirect.

3. Final Answer:

   Use flash.keep to preserve the flash for another request -> Option D

4. Quick Check:

   flash.keep extends flash life beyond one request [OK]

Hint: Use flash.keep to keep flash message for next request too [OK]

Common Mistakes:

• Using flash.now which lasts only current request
• Confusing flash.clear with preserving messages
• Using flash.delete which removes messages