Active Job framework 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 with a perform method. What is the behavior when you call MyJob.perform_later(args)?

Ruby on Rails

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

MyJob.perform_later('Alice')

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

B The job runs immediately and blocks the current thread.

C The job is discarded and never runs.

D The job raises an error because perform_later is undefined.

💡 Hint

Think about how Active Job handles background processing.

Calling perform_later adds the job to the queue to be run asynchronously by a background worker.

📝 Syntax

intermediate

Which option correctly defines a job with arguments?

You want to create a job that accepts a user ID and sends a welcome email. Which job class definition is correct?

A

class WelcomeJob < ApplicationJob
  def perform(user_id)
    UserMailer.welcome(user_id).deliver_now
  end
end

B

class WelcomeJob < ApplicationJob
  def perform
    UserMailer.welcome(user_id).deliver_now
  end
end

C

class WelcomeJob < ApplicationJob
  def perform(user)
    UserMailer.welcome(user.id).deliver_now
  end
end

D

class WelcomeJob < ApplicationJob
  def perform(user_id)
    UserMailer.welcome(user).deliver_now
  end
end

💡 Hint

The perform method must accept the arguments passed when enqueuing.

The perform method should accept the exact arguments passed to perform_later. Option A correctly accepts user_id and uses it.

🔧 Debug

advanced

Why does this job raise a NoMethodError?

Given this job code, why does it raise NoMethodError: undefined method 'send_email'?

Ruby on Rails

class EmailJob < ApplicationJob
  def perform(user)
    send_email(user)
  end
end

A Because ApplicationJob does not allow calling methods inside perform.

B Because perform must be a class method, not instance method.

C Because user argument is missing when calling perform_later.

D Because send_email is not defined in the job or included modules.

💡 Hint

Check if the method send_email is defined anywhere accessible.

The method send_email is not defined in the job class or any included module, so calling it causes a NoMethodError.

❓ state_output

advanced

What is the output after running this job with perform_now?

Consider this job and the code that runs it. What will be printed?

Ruby on Rails

class CountJob < ApplicationJob
  def perform(count)
    puts "Count is: #{count}"
  end
end

CountJob.perform_now(5)

A RuntimeError because perform_now is undefined.

B Count is: 5

C No output because perform_now does not print.

D Count is: 0

💡 Hint

perform_now runs the job immediately in the current thread.

Calling perform_now runs the job immediately, so the puts statement outputs the count value.

🧠 Conceptual

expert

Which backend adapter supports running jobs inline for testing?

In Rails Active Job, which adapter runs jobs immediately in the same process, useful for testing?

A :delayed_job

B :resque

C :inline

D :sidekiq

💡 Hint

This adapter does not queue jobs but runs them right away.

The :inline adapter runs jobs immediately in the same process, which is helpful for tests to avoid asynchronous behavior.