Scheduling Jobs

Introduction

Not every job should run immediately. Active Job provides set(wait:) and set(wait_until:) to schedule jobs for future execution.

Key Concepts

• set(wait:): Schedule after a relative duration.
• set(wait_until:): Schedule at a specific time.
• Job Chains: Jobs that schedule follow-up jobs.

Real World Context

After signup, send welcome email immediately but schedule onboarding tips for 3 days later. After an order ships, schedule a review request for 7 days out.

Deep Dive

Delayed Execution

ruby
ReminderJob.set(wait: 24.hours).perform_later(user.id)
ReportJob.set(wait_until: Date.tomorrow.noon).perform_later

Job Chaining

ruby
class OnboardingSequenceJob < ApplicationJob
  def perform(user_id, step)
    user = User.find_by(id: user_id)
    return unless user

    case step
    when 1
      OnboardingMailer.tips(user).deliver_now
      self.class.set(wait: 3.days).perform_later(user_id, 2)
    when 2
      OnboardingMailer.features(user).deliver_now
      self.class.set(wait: 7.days).perform_later(user_id, 3)
    when 3
      OnboardingMailer.feedback_request(user).deliver_now
    end
  end
end

Processing Chain

ruby
class ProcessOrderJob < ApplicationJob
  def perform(order_id)
    order = Order.find(order_id)
    order.process!
    SendConfirmationJob.perform_later(order.id)
    SyncToWarehouseJob.set(wait: 5.minutes).perform_later(order.id)
  end
end

Common Pitfalls

1. Scheduling far-future jobs without guards — Records may be deleted. Always check existence.
2. Using wall-clock time without time zones — Use in_time_zone for user-specific scheduling.

Best Practices

1. Guard against stale references — Check records still exist in delayed jobs.
2. Log scheduled times — Helps debug timing issues.

Summary

• set(wait:) for relative delays, set(wait_until:) for absolute times.
• Jobs can schedule follow-up jobs to create sequences.
• Always check record existence in delayed jobs.

# Drip email sequence
class DrippEmailJob < ApplicationJob
  def perform(user_id, step)
    user = User.find_by(id: user_id)
    return unless user&.subscribed?

    DrippMailer.send("email_#{step}", user).deliver_now
    self.class.set(wait: 3.days).perform_later(user_id, step + 1) if step < 5
  end
end