Route parameters in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a route that captures an :id parameter.

Ruby on Rails

get '/products/[1]', to: 'products#show'

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

A*id

Bid

C:id

D?id

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the colon before the parameter name.

Using a question mark or asterisk instead of a colon.

The route parameter must be prefixed with a colon : to capture it as a variable.

2fill in blank

medium

Complete the code to access the route parameter :id inside the controller action.

Ruby on Rails

def show
  @product = Product.find(params[[1]])
end

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

A:id

B'id'

Cid

D:'id'

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting quotes around the key (syntax error with bare id).

Using ":id" (accesses nonexistent params[":id"]).

In Rails controllers, route parameters are conventionally accessed using strings as keys in the params hash, like params['id']. The option 'id' is the correct string key.

3fill in blank

hard

Fix the error in the route to correctly capture a username parameter.

Ruby on Rails

get '/users/[1]', to: 'users#profile'

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

A:username

Busername

C*username

D?username

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the colon before the parameter name.

Using wildcard or query syntax instead of colon.

The route parameter must have a colon prefix to be recognized as a parameter.

4fill in blank

hard

Fill both blanks to define a nested route with :post_id and :comment_id parameters.

Ruby on Rails

get '/posts/[1]/comments/[2]', to: 'comments#show'

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

A:post_id

Bpost_id

C:comment_id

Dcomment_id

Attempts:

3 left

💡 Hint

Common Mistakes

Leaving out colons before parameter names.

Using parameter names without colon prefixes.

Both parameters must have a colon prefix to be recognized as route parameters.

5fill in blank

hard

Fill all three blanks to define a route with :category, :id, and :format parameters.

Ruby on Rails

get '/[1]/[2].[3]', to: 'items#show'

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

A:category

B:id

C:format

Dformat

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting colons before parameter names.

Not including the dot before the format parameter.

All route parameters must have a colon prefix to be recognized by Rails routing.

Practice

1. What does a route parameter in Rails do?
get '/users/:id', to: 'users#show'

easy

A. Captures part of the URL as a variable to use in the controller

B. Defines a fixed URL path without variables

C. Specifies the HTTP method to use

D. Sets the controller action to redirect to another page

Solution

1. Step 1: Understand the colon in the route path

   The colon before id means this part of the URL is a variable, called a route parameter.

2. Step 2: Role of route parameters in Rails

   This variable is captured from the URL and passed to the controller action for use, like finding a user by ID.

3. Final Answer:

   Captures part of the URL as a variable to use in the controller -> Option A

4. Quick Check:

   Route parameter = URL variable [OK]

Hint: Colon before name means URL part is a variable [OK]

Common Mistakes:

• Thinking route parameters define fixed paths
• Confusing route parameters with HTTP methods
• Assuming route parameters redirect to other pages

2. Which of the following is the correct syntax to define a route with a parameter named post_id in Rails?

easy

A. get '/posts/post_id', to: 'posts#show'

B. get '/posts/{post_id}', to: 'posts#show'

C. get '/posts/<post_id>', to: 'posts#show'

D. get '/posts/:post_id', to: 'posts#show'

Solution

1. Step 1: Identify correct route parameter syntax

   In Rails, route parameters use a colon before the name, like :post_id.

2. Step 2: Compare options

   Only get '/posts/:post_id', to: 'posts#show' uses the colon syntax correctly. Others use incorrect braces or no colon.

3. Final Answer:

   get '/posts/:post_id', to: 'posts#show' -> Option D

4. Quick Check:

   Colon before parameter name = correct syntax [OK]

Hint: Use colon before parameter name in route path [OK]

Common Mistakes:

• Using curly braces or angle brackets instead of colon
• Omitting colon before parameter name
• Confusing parameter syntax with query strings

3. Given this route:
get '/products/:id', to: 'products#show'
And this controller code:

def show
  @product_id = params[:id]
end

What will @product_id be if the URL is /products/42?

medium

A. The string '42'

B. The integer 42

C. nil

D. An error because params[:id] is undefined

Solution

1. Step 1: Understand route parameter capture

   The :id in the route captures the URL part '42' as a string in params[:id].

2. Step 2: Assigning params value in controller

   The controller assigns @product_id = params[:id], so @product_id is the string '42'. Rails does not convert it automatically to integer.

3. Final Answer:

   The string '42' -> Option A

4. Quick Check:

   Route params are strings by default [OK]

Hint: Route params are strings unless converted [OK]

Common Mistakes:

• Assuming params[:id] is an integer automatically
• Expecting nil if parameter is present
• Thinking params[:id] causes an error if defined in route

4. Identify the error in this route definition:

get '/orders/:order_id/items/:item_id', to: 'orders#item'

Controller action:

def item
  @order = Order.find(params[:id])
  @item = Item.find(params[:item_id])
end

medium

A. Route path should not have two parameters

B. params[:id] is incorrect; should be params[:order_id]

C. Controller action name should be 'show' not 'item'

D. Item.find should use params[:id] instead of params[:item_id]

Solution

1. Step 1: Check route parameters names

   The route defines parameters :order_id and :item_id, so params keys are :order_id and :item_id.

2. Step 2: Check controller parameter usage

   The controller incorrectly uses params[:id] which does not exist. It should use params[:order_id] to find the order.

3. Final Answer:

   params[:id] is incorrect; should be params[:order_id] -> Option B

4. Quick Check:

   Parameter names must match route keys [OK]

Hint: Match params keys exactly to route parameter names [OK]

Common Mistakes:

• Using generic :id when route uses :order_id
• Thinking multiple parameters are not allowed
• Confusing controller action names with route parameters

5. You want to create a nested route to show a comment belonging to a post using route parameters. Which route definition correctly captures both post_id and id for the comment?

hard

A. get '/posts/:id/comments/:post_id', to: 'comments#show'

B. get '/posts/comments/:post_id/:id', to: 'comments#show'

C. get '/posts/:post_id/comments/:id', to: 'comments#show'

D. get '/comments/:id/posts/:post_id', to: 'comments#show'

Solution

1. Step 1: Understand nested resource URL structure

   Nested routes usually put the parent resource first, then the child. Here, post_id comes before id for comment.

2. Step 2: Check route parameter order and names

   get '/posts/:post_id/comments/:id', to: 'comments#show' correctly uses /posts/:post_id/comments/:id capturing post's ID and comment's ID in order.

3. Final Answer:

   get '/posts/:post_id/comments/:id', to: 'comments#show' -> Option C

4. Quick Check:

   Parent ID first, child ID second in nested routes [OK]

Hint: Parent resource param before child in nested routes [OK]

Common Mistakes:

• Swapping order of post_id and comment id
• Putting parameters in wrong positions
• Using incorrect parameter names