Error messages and display in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to display error messages for a model in a Rails view.

Ruby on Rails

<% if @user.errors.any? %>
  <div id="error_explanation">
    <h2>[1] errors prohibited this user from being saved:</h2>
  </div>
<% end %>

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

A<%= pluralize(@user.errors.count, "error") %>

B<%= @user.errors.full_messages %>

C<%= @user.errors.count %>

D<%= @user.errors.messages %>

Attempts:

3 left

💡 Hint

Common Mistakes

Using @user.errors.full_messages directly in the header instead of the count.

Forgetting to pluralize the word 'error'.

Using @user.errors.messages which is a hash, not a string.

The pluralize helper formats the error count with correct singular/plural form, which is standard in Rails error displays.

2fill in blank

medium

Complete the code to list all error messages for a model in a Rails view.

Ruby on Rails

<ul>
  <% @user.errors.full_messages.each do |message| %>
    <li>[1]</li>
  <% end %>
</ul>

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

Amessage.full

Bmessage.to_s

[e-mail]_messages

Dmessage

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call methods on 'message' which is already a string.

Using @user.errors.full_messages inside the loop instead of the loop variable.

Inside the loop, 'message' is a string representing one error message, so just output 'message'.

3fill in blank

hard

Fix the error in the code to correctly display error messages for a model in a Rails view.

Ruby on Rails

<% if @post.errors.any? %>
  <div id="error_explanation">
    <h2>[1] errors prevented this post from saving:</h2>
    <ul>
      <% @post.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
    </ul>
  </div>
<% end %>

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

A<%= pluralize(@post.errors.count, "error") %>

B<%= @post.errors.count %>

C<%= @post.errors.full_messages.count %>

D<%= @post.errors.messages.count %>

Attempts:

3 left

💡 Hint

Common Mistakes

Using count alone without pluralize, which shows just a number without the word.

Using full_messages.count which is the same as errors.count but missing pluralize formatting.

The pluralize helper formats the error count with correct singular/plural form, which is the correct way to show error count in Rails.

4fill in blank

hard

Fill both blanks to create a Rails helper method that returns formatted error messages for a model.

Ruby on Rails

def formatted_errors(model)
  return "" if model.errors.empty?
  messages = model.errors.full_messages.map { |msg| "<li>[1]</li>" }.join
  "<ul>[2]</ul>".html_safe
end

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

Amsg

Bmessages

Cmsg.html_safe

Dmodel.errors.full_messages

Attempts:

3 left

💡 Hint

Common Mistakes

Using model.errors.full_messages directly inside the map block instead of 'msg'.

Putting the entire messages string inside each

instead of joining after mapping.

Inside map, use 'msg' to insert each message. Then wrap all messages in

tags using the 'messages' string.

5fill in blank

hard

Fill all three blanks to display error messages with a heading and list in a Rails view partial.

Ruby on Rails

<% if [1].errors.any? %>
  <div id="error_explanation">
    <h2>[2] errors prohibited this [3] from being saved:</h2>
    <ul>
      <% [1].errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
    </ul>
  </div>
<% end %>

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

A@article

B<%= pluralize(@article.errors.count, "error") %>

Carticle

D@comment

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Not pluralizing the error count in the heading.

Using instance variable syntax inside the heading string.

Use '@article' as the model variable, pluralize the error count for the heading, and use 'article' as the model name in the message.

Practice

1. In Rails, which method provides a list of user-friendly error messages for a model's validation errors?

easy

A. @model.errors.count

B. @model.errors.details

C. @model.errors.keys

D. @model.errors.full_messages

Solution

1. Step 1: Understand error message methods

   @model.errors.full_messages returns an array of readable error strings, while others return metadata or counts.

2. Step 2: Identify user-friendly output

   Only full_messages gives clear, complete error messages suitable for display.

3. Final Answer:

   @model.errors.full_messages -> Option D

4. Quick Check:

   Error messages = full_messages [OK]

Hint: Use full_messages for readable error text [OK]

Common Mistakes:

• Using errors.details which gives error codes, not messages
• Using errors.keys which lists fields, not messages
• Using errors.count which returns number, not messages

2. Which of the following is the correct way to display error messages for a @user model in a Rails view?

easy

A. <%= @user.errors.full_messages.each do |msg| %> <%= msg %> <% end %>

B. <% @user.errors.full_messages.each do |msg| %> <%= msg %> <% end %>

C. <%= @user.errors.full_messages.map { |msg| content_tag(:p, msg) } %>

D. <% @user.errors.full_messages.map { |msg| content_tag(:p, msg) } %>

Solution

1. Step 1: Understand ERB tags for iteration

   <% %> runs Ruby code without output; <%= %> outputs the result. For loops, use <% %>.

2. Step 2: Identify correct syntax for displaying messages

   <% @user.errors.full_messages.each do |msg| %>

   <%= msg %>

   <% end %> correctly uses <% %> to loop and <%= %> inside to output each message.

3. Final Answer:

   Option B -> Option B

4. Quick Check:

   Loop with <% %>, output with <%= %> [OK]

Hint: Use <% %> for loops, <%= %> for output inside loops [OK]

Common Mistakes:

• Using <%= %> for loops causing unwanted output
• Using map without outputting results
• Mixing output and code tags incorrectly

3. Given this Rails code in a view:

<ul>
  <% @post.errors.full_messages.each do |msg| %>
    <li><%= msg %></li>
  <% end %>
</ul>

What will be the output if @post.errors.full_messages contains ["Title can't be blank", "Content is too short"]?

medium

A. Title can't be blankContent is too short

B. Title can't be blankContent is too short

C. Title can't be blankContent is too short

D. No output because of syntax error

Solution

1. Step 1: Understand the loop output

   The code loops over each error message and wraps it in
2. tags inside a <ul>.

3. Step 2: Match output to HTML structure

   The output will be a <ul> list with two
4. items showing each error message.

5. Final Answer:

   <ul><li>Title can't be blank</li><li>Content is too short</li></ul> -> Option A

6. Quick Check:

   Loop creates list items inside ul [OK]

Hint: Errors inside <li> tags within <ul> show as list [OK]

Common Mistakes:

• Forgetting <ul> tags causing invalid HTML
• Not using <li> tags for each message
• Confusing output with plain text

4. You wrote this code to display errors:

<%= @article.errors.full_messages.each do |msg| %>
  <p><%= msg %></p>
<% end %>

But no errors show up in the browser. What is the problem?

medium

A. The <code><p>s

B. You must call to_s on each message before displaying

C. Using <code><%= %>s

D. The errors array is empty, so nothing shows

Solution

1. Step 1: Check ERB tag usage for loops

   Using <%= %>each, which is the original array, not the loop content.

2. Step 2: Correct loop tag usage

   Use <% %> for loops to run code without output, then use <%= %> inside for each message.

3. Final Answer:

   Using <%= %> for the loop causes output of the array, not the messages -> Option C

4. Quick Check:

   Use <% %> for loops, not <%= %> [OK]

Hint: Use <% %> for loops, <%= %> for output inside loops [OK]

Common Mistakes:

• Using <%= %> for loops causing wrong output
• Assuming errors are empty without checking
• Misunderstanding HTML tag usage inside loops

5. You want to display error messages only if there are any errors on the @comment model. Which is the best way to do this in a Rails view?

hard

A. <% if @comment.errors.any? %>
<div role='alert' aria-live='assertive'>
<ul>
<% @comment.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>

B. <div>
<ul>
<% @comment.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>

C. <% if @comment.errors.count > 0 %>
<p>Errors found</p>
<% end %>

D. <% unless @comment.errors.empty? %>
<p>Please fix errors</p>
<% end %>

Solution

1. Step 1: Check for errors presence

   Use errors.any? to check if there are any errors to display.

2. Step 2: Display errors accessibly

   Wrap errors in a div with role='alert' and aria-live='assertive' for screen readers to announce changes.

3. Step 3: Loop and show messages

   Use full_messages inside a ul with li for each error message.

4. Final Answer:

   Option A -> Option A

5. Quick Check:

   Check errors.any? and use accessible alert div [OK]

Hint: Use errors.any? and role='alert' div for accessible errors [OK]

Common Mistakes:

• Not checking if errors exist before displaying
• Missing accessibility roles for error containers
• Displaying generic messages without details