Pub/Sub Task Chaining

RegisterUser succeeds. Now you need a welcome email, a search index update, and an analytics event. You could call three more tasks from inside work — but then every change to “what happens after signup” edits the same file.

Publish a domain event when the task succeeds. Subscribers enqueue their own tasks. The registering task stays focused on creating the user.

Setup — subscriber

Listen for the event and enqueue follow-on work. ActiveSupport::Notifications is built into Rails; swap in Wisper, Kafka, or whatever your app already uses.

class SendWelcomeEmail < ApplicationTask
  required :user_id, coerce: :integer

  def work
    WelcomeMailer.with(user_id:).deliver_later
  end
end

ApplicationTask here is the base class from Background Execution with execute_later wired to TaskJob.

ActiveSupport::Notifications.subscribe("user.registered") do |*args|
  event = ActiveSupport::Notifications::Event.new(*args)
  SendWelcomeEmail.execute_later(user_id: event.payload[:user_id])
end

Usage

Put anything subscribers need on context inside work, then publish from an on_success callback.

class RegisterUser < CMDx::Task
  required :email, coerce: :string, validate: { format: URI::MailTo::EMAIL_REGEXP }
  required :name,  coerce: :string

  on_success :publish_registration_event

  def work
    context.user = User.create!(email:, name:)
  end

  private

  def publish_registration_event
    ActiveSupport::Notifications.instrument(
      "user.registered",
      user_id: context.user.id,
      email:   context.user.email
    )
  end
end

RegisterUser.execute(email: "jane@example.com", name: "Jane Doe")

Notes

Order matters

on_success runs after work finishes. Subscribers only see what you wrote to context during work — set context.user (or similar) before the callback fires.

Workflows vs pub/sub

For the next step in the same process with shared context, use a workflow. Publish events when subscribers should stay decoupled — mailers, analytics, separate queues.