Job creation and queuing in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a job is enqueued with perform_later?

Consider a Rails Active Job class SendEmailJob. When you call SendEmailJob.perform_later(user_id), what is the immediate behavior?

Ruby on Rails

class SendEmailJob < ApplicationJob
  queue_as :default

  def perform(user_id)
    # send email logic
  end
end

SendEmailJob.perform_later(42)

A The job runs immediately and blocks the current thread until done.

B The job runs synchronously but in a new thread.

C The job is discarded because perform_later is not a valid method.

D The job is added to the queue and will run asynchronously later.

💡 Hint

Think about how perform_later differs from perform_now.

Calling perform_later enqueues the job to run asynchronously using the configured queue adapter. It does not run immediately.

📝 Syntax

intermediate

Identify the correct syntax to set a custom queue in a job class

Which of the following correctly sets the queue name to :mailers in a Rails Active Job class?

Ruby on Rails

class NotificationJob < ApplicationJob
  # set queue here
  queue_as :mailers

  def perform
    # job code
  end
end

A queue_as :mailers

B self.queue = :mailers

C set_queue :mailers

D queue_name :mailers

💡 Hint

Look for the official method to assign queue names in Active Job.

The queue_as method is the correct way to specify the queue name in an Active Job class.

🔧 Debug

advanced

Why does this job never run after enqueuing?

Given the following job and code, why does the job never execute?

Ruby on Rails

class CleanupJob < ApplicationJob
  queue_as :default

  def perform
    puts "Cleaning up..."
  end
end

CleanupJob.perform_later

A The job is enqueued but no queue adapter is configured to process jobs.

B The job class is missing the <code>perform</code> method.

C The <code>perform_later</code> method requires an argument.

D The job runs immediately and finishes before output can be seen.

💡 Hint

Check if the background job processor is running or configured.

If no queue adapter or background worker is running, jobs are enqueued but never processed.

❓ state_output

advanced

What is the output after running this job with arguments?

What will be printed when the following job is enqueued and performed?

Ruby on Rails

class GreetJob < ApplicationJob
  def perform(name)
    puts "Hello, #{name}!"
  end
end

GreetJob.perform_now("Alice")

A Error: wrong number of arguments

B Hello, Alice!

C Hello, !

D No output

💡 Hint

Consider how perform_now works with arguments.

The perform_now method runs the job immediately with the given argument, printing the greeting.

🧠 Conceptual

expert

Which queue adapter supports job retries natively in Rails?

Among the default Rails queue adapters, which one supports automatic job retries without extra configuration?

A Inline adapter

B Async adapter

C Sidekiq adapter

D Test adapter

💡 Hint

Think about which adapter is designed for production background processing with retry features.

Sidekiq adapter supports retries natively by default, unlike Async or Inline adapters.