Route parameters in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Rails route helper?

Given the route get '/books/:id', to: 'books#show' and the controller action def show; render plain: params[:id]; end, what will be the output when visiting /books/42?

A The page will display the text '42'.

B The page will display the text ':id'.

C The page will show a routing error.

D The page will display the text 'books#show'.

💡 Hint

Think about how route parameters are passed to the controller.

The route captures the segment after '/books/' as the :id parameter. The controller action renders this value, so visiting '/books/42' shows '42'.

📝 Syntax

intermediate

Which route definition correctly captures a username parameter?

You want to define a route that matches URLs like /profile/johndoe and passes 'johndoe' as a parameter named username. Which route definition is correct?

A get '/profile/*username', to: 'users#show'

B get '/profile/username', to: 'users#show'

C get '/profile/:username', to: 'users#show'

D get '/profile/:id', to: 'users#show'

💡 Hint

Route parameters use a colon before the name.

Using ':username' captures that part of the URL as params[:username]. Option C treats 'username' as a fixed string, A captures a wildcard but not as a named parameter, and D uses a different parameter name.

🔧 Debug

advanced

Why does this route not capture the parameter?

Given the route get '/items/:item_id/edit', to: 'items#edit', why does visiting /items/edit cause a routing error?

A Because the controller action 'edit' is missing.

B Because the route should be defined as 'get '/items/edit/:item_id''.

C Because the route should use a query parameter instead of a route parameter.

D Because the route expects a segment between '/items/' and '/edit' to capture as :item_id, but '/items/edit' has none.

💡 Hint

Look at the URL structure and the route pattern carefully.

The route expects a URL like '/items/123/edit' where '123' is the :item_id. Visiting '/items/edit' misses that segment, so Rails cannot match the route.

❓ state_output

advanced

What is the value of params in this nested route?

Given the nested route resources :authors do resources :books end and visiting /authors/5/books/10, what will be the values of params[:author_id] and params[:id] in the BooksController?

A params[:author_id] is '5' and params[:id] is '10'.

B params[:author_id] is '10' and params[:id] is '5'.

C params[:author_id] and params[:id] are both '5'.

D params[:author_id] and params[:id] are both '10'.

💡 Hint

Nested resources pass the parent resource id with _id suffix.

In nested routes, the parent resource id is passed as params[:author_id], and the nested resource id is params[:id]. So visiting '/authors/5/books/10' sets author_id to '5' and id to '10'.

🧠 Conceptual

expert

What error occurs if a required route parameter is missing?

If a Rails route is defined as get '/orders/:order_id/items/:id', to: 'items#show' and a request is made to /orders/15/items (missing the :id), what error will Rails raise?

A ActionController::UrlGenerationError

B RoutingError

C NoMethodError

D ActiveRecord::RecordNotFound

💡 Hint

Think about how Rails matches URLs to routes.

Rails cannot match the URL '/orders/15/items' to the route requiring both :order_id and :id, so it raises a RoutingError indicating no route matches.