pure-cqrs-es-example

An implementation of a CQRS/ES system using functional FP in scala.

Goal

This is a side project for learning and experimentation purposes. It is not a "production ready" system :)

We use a simplified domain model in order to focus only on technical implementation details and functional programming principles. CQRS and Event Sourcing is a huge domain with many flavors and variations on its own.

Our goal is to implement some of the principles and ideas that we have in a purely functional way.

How to build run and test?

TODO

This is work in progress

and under heavy development. Many of the design decisions will propably change.

Domain

The domain of the project is an minimal garage management system.

Project tasks and status

• Write side server (that serves ES commands via REST API)

• Write side validator in memory store

• An event log (used for Event Sourcing) implemented in postgres

• Read side server that serves a materialized view of the log (via REST API).

• Read side server websocket support

• An alternative event log implemented using kafka

• Complete dockerized build process

• User authentication / authorization (using TSec?)

• A front SPA application (using Angular ?)

• Nginx configuration as a reverse proxy for the read/write servers

• Read side server testing

• Write side server testing

• Documentation

Stack

• Cats

• Http4s

• fs2

• Doobie

• Circe

• Docker

• Postgres

TODO Fill the list

Resources

These are some of online resources we use to learn and take inspiration from:

About Functional Programming

• Free monads and event sourcing architecture

• Introduction to tagless final

• Smart Backpacker App (core on Github)

• Scala Pet Store (on Github)

• Cats Documentation

• Doobie Documentation

About CQRS

• Clarified CQRS