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Active Outbox

A Transactional Outbox implementation for Rails and ActiveRecord.

transactional outbox pattern

This gem aims to implement the event persistance side of the pattern, focusing only on providing a seamless way to store Outbox records whenever a change occurs on a given model (#1 in the diagram). We do not provide an event publisher, nor a consumer as a part of this gem since the idea is to keep it as light weight as possible.

Motivation

If you find yourself repeatedly defining a transaction block every time you need to persist an event, it might be a sign that something needs improvement. We believe that adopting a pattern should enhance your workflow, not hinder it. Creating, updating or destroying a record should remain a familiar and smooth process.

Our primary objective is to ensure a seamless experience without imposing our own opinions or previous experiences. That's why this gem exclusively focuses on persisting records. We leave the other aspects of the pattern entirely open for your customization. You can emit these events using Sidekiq jobs, or explore more sophisticated solutions like Kafka Connect.

Why active_outbox?

  • Seamless integration with ActiveRecord
  • CRUD events out of the box
  • Ability to set custom events
  • Test helpers to easily check Outbox records are being created correctly
  • Customizable

Installation

Add this line to your application's Gemfile:

gem 'active_outbox'

And then execute:

bundle install

Or install it yourself as:

gem install active_outbox

Usage

Setup

Create the outbox table and model using the provided generator. Any model name can be passed as an argument but if empty it will default to outboxes and Outbox respectively.

rails g active_outbox:model <optional model_name>

  create  db/migrate/20231115182800_active_outbox_create_<model_name_>outboxes.rb
  create  app/models/<model_name_>outbox.rb

After running the migration, create an initializer under config/initializers/active_outbox.rb and setup the default outbox class to the new Outbox model you just created.

rails g active_outbox:install

To allow models to store Outbox records on changes, you will have to include the Outboxable concern.

# app/models/user.rb

class User < ApplicationRecord
  include ActiveOutbox::Outboxable
end

Base Events

Using the User model as an example, the default event names provided are:

  • USER_CREATED
  • USER_UPDATED
  • USER_DESTROYED

This will live under ActiveOutbox::Events wherever you include the Outboxable concern. The intent is to define it under Object for non-namespaced models, as well as under each model namespace that is encountered.

Custom Events

If you want to persist a custom event other than the provided base events, you can do so.

user.save(outbox_event: 'YOUR_CUSTOM_EVENT')

Advanced Usage

Supporting UUIDs

By default our Outbox migration has an aggregate_identifier field which serves the purpose of identifying which record was involved in the event emission. We default to integer IDs, but if you're using UUIDs as a primary key for your records you have to adjust the migrations accordingly. To do so just run the model generator with the --uuid flag.

rails g active_outbox:model <optional model_name> --uuid

Modularized Outbox Mappings

If more granularity is desired multiple outbox classes can be configured. Using the provided generators we can specify namespaces and the folder structure.

rails g active_outbox:model user_access/ --component-path packs/user_access

  create  packs/user_access/db/migrate/20231115181205_active_outbox_create_user_access_outboxes.rb
  create  packs/user_access/app/models/user_access/outbox.rb

After creating the needed Outbox classes for each module you can specify multiple mappings in the initializer.

# frozen_string_literal: true

Rails.application.reloader.to_prepare do
  ActiveOutbox.configure do |config|
    config.outbox_mapping = {
      'member' => 'Member::Outbox',
      'user_access' => 'UserAccess::Outbox'
    }
  end
end

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/rootstrap/active_outbox. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the ActiveOutbox project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.