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.

Practice

1. What is the main purpose of using nested routes in a Rails application?

easy

A. To speed up database queries automatically

B. To group related resources and show their connection in URLs

C. To create routes without controllers

D. To avoid using RESTful conventions

Solution

1. Step 1: Understand nested routes concept

   Nested routes group related resources in URLs to reflect their relationship, like a parent and its children.

2. Step 2: Identify the purpose in URL structure

   This grouping helps keep URLs organized and meaningful, showing the connection between resources.

3. Final Answer:

   To group related resources and show their connection in URLs -> Option B

4. Quick Check:

   Nested routes = Group related resources [OK]

Hint: Nested routes show parent-child URL relationships clearly [OK]

Common Mistakes:

• Thinking nested routes speed up queries
• Believing nested routes remove need for controllers
• Assuming nested routes ignore RESTful design

2. Which of the following is the correct syntax to define a nested route for comments inside posts in Rails?

easy

A. resources :comments do
resources :posts
end

B. resource :posts, :comments

C. resources :posts do
resources :comments
end

D. resources :posts, nested: :comments

Solution

1. Step 1: Recall nested route syntax

   In Rails, nested routes are defined by placing resources :child inside a block of resources :parent.

2. Step 2: Match syntax to example

   resources :posts do resources :comments end correctly nests comments inside posts using a block.

3. Final Answer:

   resources :posts do resources :comments end -> Option C

4. Quick Check:

   Nested routes syntax = block inside parent resource [OK]

Hint: Use block syntax: parent do child end [OK]

Common Mistakes:

• Reversing parent and child resources
• Using commas instead of blocks
• Using singular resource instead of plural

3. Given the nested routes below, what is the URL helper for editing a comment with ID 5 belonging to post with ID 3?

resources :posts do
  resources :comments
end

medium

A. edit_post_comment_path(3, 5)

B. edit_comment_path(5)

C. edit_post_path(3, 5)

D. edit_comments_post_path(5, 3)

Solution

1. Step 1: Understand nested URL helpers

   For nested routes, the helper includes both parent and child resource names and IDs, like edit_post_comment_path(post_id, comment_id).

2. Step 2: Match IDs to parameters

   Post ID is 3, comment ID is 5, so the helper is edit_post_comment_path(3, 5).

3. Final Answer:

   edit_post_comment_path(3, 5) -> Option A

4. Quick Check:

   Nested helper = edit_parent_child_path(parent_id, child_id) [OK]

Hint: Nested helpers need parent ID first, then child ID [OK]

Common Mistakes:

• Using only child ID in helper
• Swapping parent and child IDs
• Using plural instead of singular in helper

4. Identify the error in the following nested routes definition:

resources :authors do
  resources :books
resources :publishers
end

medium

A. Should use resource instead of resources for books

B. Cannot nest resources :publishers inside resources :authors

C. No error, syntax is correct

D. Missing end for the resources :authors block

Solution

1. Step 1: Check block structure

   The resources :authors block opens but does not close before defining resources :publishers.

2. Step 2: Confirm correct nesting

   Each block must have a matching end. Here, resources :publishers is outside the intended block but inside the authors block without closure.

3. Final Answer:

   Missing end for the resources :authors block -> Option D

4. Quick Check:

   Every block needs matching end [OK]

Hint: Count your do/end pairs carefully [OK]

Common Mistakes:

• Forgetting to close blocks with end
• Nesting unrelated resources incorrectly
• Confusing singular and plural resource keywords

5. You want to create nested routes for projects and their tasks, but only allow index and show actions for tasks. Which is the correct way to define this in Rails?

hard

A. resources :projects do
resources :tasks, only: [:index, :show]
end

B. resources :projects do
resources :tasks, except: [:index, :show]
end

C. resources :projects, only: [:index, :show] do
resources :tasks
end

D. resources :projects do
resource :tasks, only: [:index, :show]
end

Solution

1. Step 1: Use nested resources with action limits

   To limit actions on nested resources, use only: [:index, :show] inside the nested resources block.

2. Step 2: Verify correct syntax

   resources :projects do resources :tasks, only: [:index, :show] end correctly nests tasks inside projects and limits actions to index and show.

3. Final Answer:

   resources :projects do resources :tasks, only: [:index, :show] end -> Option A

4. Quick Check:

   Limit nested actions with only: [OK]

Hint: Use only: to limit nested resource actions [OK]

Common Mistakes:

• Using except instead of only
• Limiting actions on parent instead of child
• Using singular resource for multiple tasks