Partial templates in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What will this partial render output?

Given the following Rails partial and render call, what will be the output on the page?

Ruby on Rails

<!-- _item.html.erb -->
<p>Item: <%= item.name %></p>

<!-- In a view -->
<%= render partial: 'item', locals: { item: OpenStruct.new(name: 'Book') } %>

A <p>Item: item.name</p>

B <p>Item: </p>

C <p>Item: Book</p>

D Error: undefined local variable or method `item`

💡 Hint

Remember that locals passed to partials become local variables inside the partial.

The partial receives the local variable 'item' with a name attribute 'Book'. It renders the paragraph with that value.

📝 Syntax

intermediate

Which render call correctly passes a collection to a partial?

You have a partial '_product.html.erb' expecting a local variable 'product'. Which render call correctly renders it for each product in @products?

A <%= render partial: 'product', collection: @products %>

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

C <%= render 'product', product: @products %>

D <%= render partial: 'product', object: @products %>

💡 Hint

Look for the Rails convention to render a collection with a partial.

Option A uses the correct 'collection' key to render the partial for each item in @products, assigning each item to 'product'.

🔧 Debug

advanced

Why does this partial raise an error?

Given this partial and render call, why does it raise an error? Partial (_user.html.erb):

Name: <%= user.name %>

Render call:

<%= render 'user' %>

A Rails does not support rendering partials without locals.

B The partial filename is incorrect; it should be '_users.html.erb'.

C The render call must use 'partial:' keyword explicitly.

D The local variable 'user' is not passed, so it's undefined in the partial.

💡 Hint

Check if the partial expects any local variables and if they are passed.

The partial uses 'user' variable but the render call does not pass any locals, so 'user' is undefined causing an error.

❓ state_output

advanced

What is the output count of this partial rendering?

If @comments has 3 comment objects, what is the number of

elements rendered by this code? Code:

  <%= render partial: 'comment', collection: @comments %>

Partial (_comment.html.erb):

<%= comment.body %>

A 1 <li> element with all comments concatenated

B 3 <li> elements

C 0 <li> elements because partial is not passed a local variable

D Error due to missing 'as' option in render

💡 Hint

Rendering a collection renders the partial once per item.

Each comment in @comments renders one

element, so total 3

elements appear inside the

.

🧠 Conceptual

expert

What error occurs if you render a partial with a missing local variable?

Consider this partial '_profile.html.erb' that uses a local variable 'profile'. What error will Rails raise if you render it without passing 'profile'?

Ruby on Rails

<p>User: <%= profile.user_name %></p>

A NameError: undefined local variable or method `profile`

B SyntaxError: unexpected local variable

C NoMethodError: undefined method `user_name` for nil:NilClass

D ArgumentError: missing required local variable 'profile'

💡 Hint

Think about what happens when a variable is referenced but not defined in Ruby.

Since 'profile' is not defined in the partial's scope, Ruby raises a NameError for undefined local variable or method.