Nested routes in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What URL does this nested route generate?

Given the following Rails routes configuration, what is the URL helper output for post_comment_path(5, 10)?

Ruby on Rails

Rails.application.routes.draw do
  resources :posts do
    resources :comments
  end
end

A "/posts/5/comments/10"

B "/comments/10/posts/5"

C "/posts/10/comments/5"

D "/comments/5/posts/10"

💡 Hint

Remember nested routes include the parent resource's ID first.

In nested routes, the URL includes the parent resource ID first, then the nested resource ID. So post_comment_path(5, 10) generates /posts/5/comments/10.

📝 Syntax

intermediate

Which nested route declaration is valid?

Which of the following nested route declarations is syntactically correct in Rails?

A

resources :posts
  resources :comments
end

B

resources :posts {
  resources :comments
}

C

resources :posts => {
  resources :comments
}

D

resources :posts do
  resources :comments
end

💡 Hint

Rails uses do...end blocks for nested routes.

Rails nested routes use do...end blocks. Curly braces or hash rockets are not valid here.

❓ state_output

advanced

What controller and action does this nested route call?

Given this nested route and a GET request to /posts/3/comments/7/edit, which controller and action will handle the request?

Ruby on Rails

Rails.application.routes.draw do
  resources :posts do
    resources :comments
  end
end

A CommentsController#edit

B PostsController#edit

C PostsController#show

D CommentsController#show

💡 Hint

The URL ends with /edit on a nested resource.

The URL /posts/3/comments/7/edit targets the edit action of the CommentsController because comments are nested inside posts.

🔧 Debug

advanced

Why does this nested route URL helper raise an error?

Given this routes file, why does calling post_comment_path(10) raise an error?

Ruby on Rails

Rails.application.routes.draw do
  resources :posts do
    resources :comments
  end
end

A post_comment_path is not defined for nested routes.

B Missing the post ID argument; nested routes require both post and comment IDs.

C The routes file is missing a root route, causing all helpers to fail.

D post_comment_path expects only one argument, so two are needed.

💡 Hint

Nested routes require IDs for both parent and child resources.

Because comments are nested inside posts, the helper post_comment_path requires two IDs: the post ID and the comment ID. Passing only one ID causes an argument error.

🧠 Conceptual

expert

How many routes are created by this nested resources declaration?

How many distinct routes are generated by this nested route declaration?

resources :authors do
  resources :books
end

A 10

B 7

C 14

D 21

💡 Hint

Each resource generates 7 RESTful routes; nesting multiplies them.

Each resources generates 7 routes (index, show, new, create, edit, update, destroy). Nesting books inside authors creates 7 routes for authors plus 7 nested routes for books, totaling 14.