An example about DDD Service

Based on Domain-Driven Design and Event-Driven architecture, and using the following technologies

• web framework: Connexion
• server workers: Gunicorn with Uvicorn worker
• ORM: SQLAlchemy
• database migration tool: Alembic
• message queue: pika

Develop new service

Prepare Python virtual env

• python: version >= 3.11
• pyenv: https://github.com/pyenv/pyenv
• pyenv-virtualenv: https://github.com/pyenv/pyenv-virtualenv

pyenv virtualenv new-service
pyenv activate new-service
pip install pip wheel setuptools -U
pip install -r requirements_local.txt

Init

1. cd /path/to/new-service
2. python /path/to/ddd-service-example/copy_tool.py init
3. pip install -r requirements.txt -r requirements_local.txt -r requirements_test.txt
4. update setting in app/config.py
   • database_url
   • postgres_schema
   • rabbitmq_exchange_name
   • rabbitmq_consumer_name

Add bounded context

1. python /path/to/ddd-service-example/copy_tool.py add bounded_context_name
2. start coding
   • value object
   • event
   • entity
   • use case
   • orm
   • repository
   • controller
   • event handler
   • handler
   • swagger (openapi)

Add message queue exchange handler

1. python /path/to/ddd-service-example/copy_tool.py add_message_queue_handler exchange_name
2. start coding
   • payload
   • exchange handler
   • app/message_queue_consumer.py

Set local PostgreSQL database

1. use database_username, database_password in app/config.py to create local PostgreSQL database

# if database_username is `postgres`
brew install postgresql@15
brew services start postgresql@15
createuser -P -d postgres
createdb -O "postgres" default

Update local database

1. make build-migration message='migration message'
2. make migrate-database

Set local RabbitMQ

docker run -it --rm --name rabbitmq -p 5672:5672 -p 15672:15672 -e RABBITMQ_DEFAULT_USER=root -e RABBITMQ_DEFAULT_PASS=1234 rabbitmq:management

Run locally

• server: make local-run
• mq consumer: make local-run-consumer

Debugging in VSCode

1. select the Debugging icon > Run and Debug