Passing data to partials in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to render a partial named '_item.html.erb'.

Ruby on Rails

<%= render [1] %>

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

Atemplate: 'item'

Bpartial: 'item'

Cpartial: :item

D'item'

Attempts:

3 left

💡 Hint

Common Mistakes

Including the underscore in the partial name.

Using 'template' instead of just the partial name string.

In Rails, to render a partial named '_item.html.erb', you use render 'item'.

2fill in blank

medium

Complete the code to pass a local variable named 'item' to the partial.

Ruby on Rails

<%= render 'item', [1]: {item: @item} %>

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

Alocals_hash

Blocal

Clocals

Dlocals:

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'local' instead of 'locals'.

Adding a colon after 'locals' incorrectly.

To pass local variables to a partial, use the locals option with a hash.

3fill in blank

hard

Fix the error in passing a local variable named 'user' to the partial.

Ruby on Rails

<%= render 'profile', locals: [1] %>

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

A{user}

B{user: user}

Cuser

Duser: user

Attempts:

3 left

💡 Hint

Common Mistakes

Passing just the variable without a hash.

Using curly braces without key-value pairs.

The locals option expects a hash with keys as variable names and values as their values, like {user: user}.

4fill in blank

hard

Fill the blank to pass two local variables 'post' and 'comments' to the partial.

Ruby on Rails

<%= render 'post', [1]: {post: post, comments: comments} %>

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

Alocals

Blocal

Clocals_hash

Dlocals:

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'local' instead of 'locals'.

Repeating the option name for each variable.

Use the locals option once with a hash containing all local variables.

5fill in blank

hard

Fill the blank to render a partial with local variables 'article', 'author', and 'tags'.

Ruby on Rails

<%= render 'article', [1]: {article: article, author: author, tags: tags} %>

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

Alocals

Barticle

Cauthor

Dtags

Attempts:

3 left

💡 Hint

Common Mistakes

Not using the locals option.

Passing variables without keys.

The locals option is used with a hash of local variables. The variables are keys and values in the hash.

Practice

1. What is the main purpose of using locals when rendering partials in Rails?

easy

A. To create a new controller action

B. To include JavaScript files in the partial

C. To define CSS styles for the partial

D. To pass data as local variables to the partial

Solution

1. Step 1: Understand partials in Rails

   Partials are reusable view templates that help keep code DRY (Don't Repeat Yourself).

2. Step 2: Role of locals

   The locals option lets you pass data as local variables to the partial, making it flexible and dynamic.

3. Final Answer:

   To pass data as local variables to the partial -> Option D

4. Quick Check:

   Passing data to partials = locals [OK]

Hint: Remember: locals pass data inside partials [OK]

Common Mistakes:

• Confusing locals with JavaScript or CSS inclusion
• Thinking partials create controller actions
• Assuming locals define styles

2. Which of the following is the correct syntax to pass a local variable named user with value @user to a partial called _profile.html.erb?

easy

A. <%= render partial: profile, user: @user %>

B. <%= render 'profile', locals: { user: @user } %>

C. <%= render profile, user: @user %>

D. <%= render partial: 'profile', locals: user: @user %>

Solution

1. Step 1: Identify correct render syntax with locals

   The correct way to pass locals is using locals: { key: value } inside the render call.

2. Step 2: Check each option

   <%= render 'profile', locals: { user: @user } %> uses locals: { user: @user } which is correct syntax. Others miss the locals hash or have wrong syntax.

3. Final Answer:

   <%= render 'profile', locals: { user: @user } %> -> Option B

4. Quick Check:

   Use locals hash to pass variables [OK]

Hint: Use locals: { var: value } to pass data [OK]

Common Mistakes:

• Omitting the locals keyword
• Passing variables directly without locals hash
• Incorrect hash syntax for locals

3. Given the following code in a Rails view:

user = User.new(name: 'Alice')
<%= render 'user_info', locals: { user: user } %>

And the partial _user_info.html.erb contains:

<p>Name: <%= user.name %></p>

What will be the rendered output?

medium

A. Name: Alice

B. Name:

C. Error: undefined local variable 'user'

D. Name: user

Solution

1. Step 1: Understand locals passing

   The variable user is passed as a local variable to the partial with value User.new(name: 'Alice').

2. Step 2: Partial uses user.name

   The partial accesses user.name, which is 'Alice', so it renders the name correctly.

3. Final Answer:

   <p>Name: Alice</p> -> Option A

4. Quick Check:

   Locals pass data correctly = Alice shown [OK]

Hint: Locals become variables inside partial [OK]

Common Mistakes:

• Forgetting to pass locals causes undefined variable error
• Assuming instance variables are automatically available
• Confusing variable names inside partial

4. Identify the error in this code snippet:

<%= render partial: 'comment', locals: { comment: @comment } %>

# In _comment.html.erb
<p><%= comment_text %></p>

What will happen when this view is rendered?

medium

A. Error: undefined local variable or method 'comment_text'

B. Renders the comment text correctly

C. Syntax error in render call

D. Renders nothing inside the paragraph

Solution

1. Step 1: Check locals passed to partial

   The locals hash passes comment: @comment, so inside the partial the variable comment is available.

2. Step 2: Check variable used in partial

   The partial uses comment_text, which is not defined or passed, causing an undefined variable error.

3. Final Answer:

   Error: undefined local variable or method 'comment_text' -> Option A

4. Quick Check:

   Variable name mismatch causes error [OK]

Hint: Variable names must match locals keys exactly [OK]

Common Mistakes:

• Using wrong variable name inside partial
• Assuming instance variables are available without passing
• Not passing required locals

5. You want to render a list of products using a partial _product.html.erb and pass each product as a local variable named item. Which code correctly renders the list with locals?

hard

A. <%= render product, collection: @products, as: :item %>

B. <%= render partial: 'product', collection: @products, locals: { item: product } %>

C. <%= render partial: 'product', collection: @products, as: :item %>

D. <% @products.each do |p| %>
<%= render 'product', locals: { item: product } %>
<% end %>

Solution

1. Step 1: Understand rendering collections with locals

   Rails allows rendering a collection with render partial: 'name', collection: array, as: :var to pass each element as a local variable.

2. Step 2: Check each option

   <%= render partial: 'product', collection: @products, as: :item %> correctly uses partial, collection, and as: :item to pass each product as item local variable. The <% @products.each do |p| %> <%= render 'product', locals: { item: product } %> <% end %> uses manual loop but product is undefined (loop var is p). The <%= render partial: 'product', collection: @products, locals: { item: product } %> has wrong locals usage (product undefined). The <%= render product, collection: @products, as: :item %> misses partial keyword and unquoted product undefined.

3. Final Answer:

   <%= render partial: 'product', collection: @products, as: :item %> -> Option C

4. Quick Check:

   Use collection + as for locals in partial [OK]

Hint: Use collection and as: :var for lists [OK]

Common Mistakes:

• Passing locals inside collection render incorrectly
• Forgetting to use as: to rename local variable
• Using manual loops instead of collection render