DDDemo

A minimal example for a scalable, easy-to-maintain Domain Driven Design repository.

Summary

This repository features a monolith backend service containing a single module orders. The module contains only one feature: create an order. When a new order is created, it publishes an OrderCreated event which triggers handler executions in the subdomains that subscribes to that event, i.e. notifications and invoices services.

Highlights

Handling domain events via observer pattern, i.e. EventPublisher and EventSubscriber.
Vertical slice architecture. The project structure follows the concepts of the relevant domains and subdomains, without explicitly using the technical DDD terms.
Grouping side-effects per event (subscribeOrderCreatedEvents), enabling a quick glance of all side-effects involved from an event.
Hexagonal architecture. The repository splits the domain and adapter implementations following the hexagonal architecture pattern, without explicitly using the technical HA terms e.g. no mentions of domains, ports or adapters.
CQRS (currently only contains a single command.)

Overview

Architecture Diagram

Directories

PROJECT_ROOT
├── cmd -------------------------------> monolith app 
│   ├── main.go
│   └── monolith
├── internal/ -------------------------> supporting files for monolith
├── orders
│   ├── internal
│   │   ├── app -----------------------> service app (CQRS style)
│   │   │   ├── app.go
│   │   │   ├── commands/
│   │   │   └── queries/
│   │   ├── orders
│   │   │   ├── event.go --------------> contains domain events
│   │   │   ├── event_handler.go ------> event handler interface for subdomains
│   │   │   ├── handler.go ------------> available order service functions
│   │   │   ├── invoices/ -------------> order subdomain 1
│   │   │   ├── notifications/ --------> order subdomain 2
│   │   │   └── ...
│   │   └── payments/ ------------------> external domain
│   └── module.go ---------------------> service setup. check this first.
└── README.md

Acknowledgements

This project took many inspirations from the project https://github.com/PacktPublishing/Event-Driven-Architecture-in-Golang, which provides a more complex example. While the general idea is the same, the implementation greatly differs. This repository opts for a vertical slice architecure on top of the DDD pattern, and grouping the domain event subscription per event rather than per service.

djiwandou / dddemo