This repository contains Python code examples demonstrating various aspects of Event Sourcing, a design pattern for persisting data changes as a sequence of events.
The goal is to demonstrate usage of different approaches using python only. In the most basic way possible. To remove any dependencies and focus on the core concepts.
- Basic Event Store: A simple implementation using a
defaultdictfor in-memory storage. - Command and Event Handling: Demonstrates how to create commands, process them, and persisting events.
- Projection: Projection of an event into a table.
- CQRS: Example of Command Query Responsibility Segregation with a separate read model.
- Querying Event Streams and Projections: Examples of querying events directly and using materialized views.
- Test: All examples come with a test
- Aggregate: Demonstrates how to group related events into an aggregate.
- Workflows: Applying ES to run multi step operations.
- Snapshotting: How to use snapshots
- Data pruning: pruning old events to manage storage costs.
- Data erase: Encrytion shredding
- Copy and paste
docker-compose buildto build docker image - Copy and paste
docker-compose up -dto spin up docker image
Once docker is running you can access container using command below:
docker exec -it python-es-python-app-1 bash.
- Within docker container, run
pytest.
Refer to the tests folder for example usage.
Example use of commands:
app/tests/test_create_post_command.py- shows a basic use of a command with an event being persisted.app/tests/test_publish_post_command.py- shows a command that has validation in place. Validation checks if command can be executed.
Example use of projections:
app/tests/test_project_posts.py- show an example of how we can listen to events. Projection is just one example of a side effect.