Route constraints in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a constraint that only allows numeric IDs in the route.

Ruby on Rails

get '/products/:id', to: 'products#show', constraints: { id: /[1]/ }

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

A[A-Z]+

B[a-z]+

C\w+

D\d+

Attempts:

3 left

💡 Hint

Common Mistakes

Using letters instead of digits in the regex.

Forgetting to escape backslashes.

The regex \d+ matches one or more digits, ensuring the :id parameter is numeric.

2fill in blank

medium

Complete the code to restrict the route to only accept HTTP GET requests.

Ruby on Rails

match '/search', to: 'search#index', via: :[1]

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

Apost

Bdelete

Cget

Dput

Attempts:

3 left

💡 Hint

Common Mistakes

Using POST or other HTTP methods instead of GET.

The via: :get option restricts the route to only respond to GET requests.

3fill in blank

hard

Fix the error in the route constraint to only allow lowercase letters for the username parameter.

Ruby on Rails

get '/users/:username', to: 'users#show', constraints: { username: /[1]/ }

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

A[a-z]+

B[A-Z]+

C[a-zA-Z]+

D\d+

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase or digits in the regex.

Using a regex that allows uppercase letters.

The regex [a-z]+ matches one or more lowercase letters, restricting the username accordingly.

4fill in blank

hard

Fill both blanks to create a route that only matches subdomains 'admin' or 'api'.

Ruby on Rails

constraints subdomain: /[1]|[2]/ do
  get '/dashboard', to: 'dashboard#index'
end

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

Aadmin

Buser

Capi

Dguest

Attempts:

3 left

💡 Hint

Common Mistakes

Including subdomains not intended to match.

Using commas instead of pipe in regex.

The regex admin|api matches either 'admin' or 'api' subdomains for the route.

5fill in blank

hard

Fill all three blanks to define a route with constraints on HTTP method, subdomain, and numeric ID.

Ruby on Rails

constraints subdomain: /[1]/ do
  match '/items/:id', to: 'items#show', via: :[2], constraints: { id: /[3]/ }
end

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

Aapi

Bget

C\d+

Dadmin

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong subdomain or HTTP method.

Not using regex for numeric ID.

The route matches requests on the 'admin' subdomain, only GET method, and numeric IDs using \d+.

Practice

1. What is the main purpose of using route constraints in a Rails application?

easy

A. To style the HTML output of views

B. To speed up database queries automatically

C. To manage user sessions and cookies

D. To limit which URLs match routes based on specific patterns or conditions

Solution

1. Step 1: Understand what route constraints do

   Route constraints restrict which URLs can match a route by applying conditions like regex or subdomain checks.

2. Step 2: Compare options to the purpose of constraints

   Only To limit which URLs match routes based on specific patterns or conditions describes limiting URL matches based on patterns or conditions, which is the core use of route constraints.

3. Final Answer:

   To limit which URLs match routes based on specific patterns or conditions -> Option D

4. Quick Check:

   Route constraints = limit URL matches [OK]

Hint: Route constraints control which URLs reach your routes [OK]

Common Mistakes:

• Confusing route constraints with database or view logic
• Thinking constraints manage sessions or cookies
• Assuming constraints style HTML output

2. Which of the following is the correct syntax to add a regex constraint for a route parameter :id that only allows digits?

easy

A. get '/items/:id', to: 'items#show', constraints: { id: /\d+/ }

B. get '/items/:id', to: 'items#show', constraints: { id: '[a-z]+' }

C. get '/items/:id', to: 'items#show', constraints: { id: /[a-z]+/ }

D. get '/items/:id', to: 'items#show', constraints: { id: /\w+/ }

Solution

1. Step 1: Identify regex for digits only

   The regex /\d+/ matches one or more digits, which fits the requirement.

2. Step 2: Check syntax for constraints hash

   The syntax constraints: { id: /\d+/ } correctly applies the regex constraint to the :id parameter.

3. Final Answer:

   get '/items/:id', to: 'items#show', constraints: { id: /\d+/ } -> Option A

4. Quick Check:

   Regex for digits = /\d+/ [OK]

Hint: Use /\d+/ regex for digit-only route params [OK]

Common Mistakes:

• Using string instead of regex for constraints
• Using wrong regex like /[a-z]+/ for digits
• Missing double backslash escape in regex

3. Given the route definition below, what URL will match the route?

get '/profile/:username', to: 'users#show', constraints: { username: /[a-z]{3,}/ }

medium

A. /profile/alex

B. /profile/Jo

C. /profile/123

D. /profile/Alice

Solution

1. Step 1: Understand the regex constraint

   The regex /[a-z]{3,}/ means the username must be at least 3 lowercase letters.

2. Step 2: Check each URL against the regex

   "/profile/Jo" fails because "Jo" has uppercase and only 2 letters.
   "/profile/alex" matches because "alex" is lowercase and 4 letters.
   "/profile/123" fails because digits are not allowed.
   "/profile/Alice" fails because of uppercase 'A'.

3. Final Answer:

   /profile/alex -> Option A

4. Quick Check:

   Regex requires lowercase 3+ letters = /profile/alex/ [OK]

Hint: Match regex carefully: lowercase letters only, length matters [OK]

Common Mistakes:

• Ignoring case sensitivity in regex
• Assuming digits match letter regex
• Not counting minimum length in regex

4. Identify the error in this route constraint code snippet:

get '/orders/:order_id', to: 'orders#show', constraints: { order_id: '\\d+' }

medium

A. The route path is missing a leading slash

B. The controller action is incorrect

C. The regex is a string, it should be a Regexp object

D. The constraints hash key should be a symbol, not a string

Solution

1. Step 1: Check the constraints value type

   The value '\\d+' is a string, but Rails expects a Regexp object for regex constraints.

2. Step 2: Confirm correct regex syntax

   It should be /\d+/ (a Regexp literal), not a string '\\d+'.

3. Final Answer:

   The regex is a string, it should be a Regexp object -> Option C

4. Quick Check:

   Regex constraints need Regexp objects, not strings [OK]

Hint: Use /regex/ not 'string' for route constraints [OK]

Common Mistakes:

• Using string instead of Regexp for constraints
• Confusing route path syntax
• Misnaming controller or action

5. You want to restrict a route to only respond when the subdomain is 'admin'. Which of the following route definitions correctly applies this constraint?

hard

A. get '/dashboard', to: 'admin#dashboard', constraints: { subdomain: 'admin' }

B. get '/dashboard', to: 'admin#dashboard', constraints: lambda { |req| req.subdomain == 'admin' }

C. get '/dashboard', to: 'admin#dashboard', constraints: { domain: 'admin' }

D. get '/dashboard', to: 'admin#dashboard', constraints: { subdomain: /admin/ }

Solution

1. Step 1: Understand subdomain constraints options

   Rails allows constraints as regex, hash, or custom objects like lambdas for complex logic.

2. Step 2: Evaluate each option

   get '/dashboard', to: 'admin#dashboard', constraints: { subdomain: 'admin' } uses a string for subdomain, which is not valid.
   get '/dashboard', to: 'admin#dashboard', constraints: { subdomain: /admin/ } uses regex /admin/, which matches subdomain 'admin' but may match partials.
   get '/dashboard', to: 'admin#dashboard', constraints: lambda { |req| req.subdomain == 'admin' } uses a lambda checking if request subdomain equals 'admin', which is precise and recommended.
   get '/dashboard', to: 'admin#dashboard', constraints: { domain: 'admin' } uses 'domain' key, which is incorrect for subdomain constraints.

3. Final Answer:

   get '/dashboard', to: 'admin#dashboard', constraints: lambda { |req| req.subdomain == 'admin' } -> Option B

4. Quick Check:

   Use lambda for precise subdomain check [OK]

Hint: Use lambda for exact subdomain constraints [OK]

Common Mistakes:

• Using string instead of lambda or regex for subdomain
• Confusing domain with subdomain key
• Using regex that matches partial subdomains unintentionally