cqrs-es-sample-with-res

CQRS with Event Sourcing sample app using Rails Event Store. See it live.

Order management app

This application simulates a process of managing orders.

We start with a list of exiting products and customers (populated with seeds).

Setup

Postgresql

Docker

If you would like to use Docker image with PostgreSQL provided by us, run docker-compose up -d. Your done for this step.

PostgreSQL installed in the system

If you have PostgreSQL installed directly in your system and prefer to use it, create

• .env.development.local containing:

DATABASE_URL=postgresql:///cqrs-es-sample-with-res_development

• .env.test.local containing:

DATABASE_URL=postgresql:///cqrs-es-sample-with-res_test

It should would work for most of the cases. If you have more sophisticated setup, you need to update DATABASE_URL accordingly.

Application

Run make dev to install dependencies, create db, setup schema and seed data.

Run bin/rails s to start the web server.

UI flow

Customer perspective

The customer perspective is "simulated" only - via using the select box.

• Add/remove some of the existing products to the order
• Choose the customer
• Submit the order
  • after this you can't update the order items or customer
  • it generates the order number like "2021/03/20" (the last part is random(100))
• Look at the order
• Look at the history of events (in the Rails Event Store Browser)

Admin perspective

In /admin we show how to combine the ActiveAdmin gem with the DDD/event-driven approach. We do it via limiting the typical CRUD actions. All the "view" options are still there.

Admin can cancel an order in the admin panel.

Domains

Domains exist in directories at the root level of the Rails app.

Ordering

The Ordering::Order aggregate manages the state machine of an order:

• draft
• submitted
• paid
• expired
• cancelled

After each successful change an appropriate event is published in the Order stream. This object is fully event sourced.

Order	draft	submitted	paid	expired	cancelled
draft		✅		✅
submitted			✅		✅
paid
expired
cancelled

Payments

The Payments::Payment aggregate manages the following states:

• authorized
• captured
• released

This Order object is fully event sourced.

Product Catalog

We implement this domain as a CRUD-based bounded context. The goal is to present how to deal with such CRUD-ish domains and to show how to integrate it with parts of the system.

It's just a single ActiveRecord Product class.

We wrap it with a ProductCatalog namespace to explicitly set its boundaries.

This Bounded Context has both - the write part and the read part as the same model. You can say it's not really CQRS - which is true for many CRUDish bounded contexts.

Read models

There's only one read model - which helps us listing all the orders and individual order details.

It consists of 2 ActiveRecord classes: Order and OrderItem.

Process Managers

1. Release payments when order expired

There's a process manager responsible for dealing with the process of expiring orders.

It takes the following events as the input:

• Ordering::OrderSubmitted
• Ordering::OrderExpired
• Ordering::OrderPaid
• Payments::PaymentAuthorized
• Payments::PaymentReleased

When certain conditions are met the process manager return a ReleasePayment command.

2. Confirm order when payment successful

Another process manager is responsible for confirming order. It does it, when a successful payment is detected.

I like it, where can I learn more about all those DDD concepts?

Over time we have developed a number of DDD-related online courses. We now sell them as part of 1 membership access via https://arkademy.dev for $49/month.