Event Sourcing in Python with EventStoreDB

This package supports using the Python eventsourcing library with EventStoreDB. It uses the esdbclient package to communicate with EventStoreDB via its gRPC interface.

Installation

Use pip to install the stable distribution from the Python Package Index.

$ pip install eventsourcing-eventstoredb

Please note, it is recommended to install Python packages into a Python virtual environment.

Getting started

Define aggregates and applications in the usual way. Please note, aggregate sequences in EventStoreDB start from position 0, so set INITIAL_VERSION on your aggregate classes accordingly.

from eventsourcing.application import Application
from eventsourcing.domain import Aggregate, event


class TrainingSchool(Application):
    def register(self, name):
        dog = Dog(name)
        self.save(dog)
        return dog.id

    def add_trick(self, dog_id, trick):
        dog = self.repository.get(dog_id)
        dog.add_trick(trick)
        self.save(dog)

    def get_dog(self, dog_id):
        dog = self.repository.get(dog_id)
        return {'name': dog.name, 'tricks': list(dog.tricks)}


class Dog(Aggregate):
    INITIAL_VERSION = 0

    @event('Registered')
    def __init__(self, name):
        self.name = name
        self.tricks = []

    @event('TrickAdded')
    def add_trick(self, trick):
        self.tricks.append(trick)

Configure the application to use EventStoreDB. Set environment variable PERSISTENCE_MODULE to 'eventsourcing_eventstoredb', and set EVENTSTOREDB_URI to the host and port of your EventStoreDB.

school = TrainingSchool(env={
    'PERSISTENCE_MODULE': 'eventsourcing_eventstoredb',
    'EVENTSTOREDB_URI': 'localhost:2113',
})

NB: SSL/TLS not yet supported: In case you are running against a cluster, or want to use SSL/TLS certificates, you can specify these things in the URI.

    'EVENTSTOREDB_URI': 'esdb://localhost:2111,localhost:2112,localhost:2113?tls&rootCertificate=./certs/ca/ca.crt'

The application's methods may be then called, from tests and user interfaces.

dog_id = school.register('Fido')
school.add_trick(dog_id, 'roll over')
school.add_trick(dog_id, 'play dead')
dog_details = school.get_dog(dog_id)
assert dog_details['name'] == 'Fido'
assert dog_details['tricks'] == ['roll over', 'play dead']

To see the events have been saved, we can reconstruct the application and get Fido's details again.

school = TrainingSchool(env={
    'PERSISTENCE_MODULE': 'eventsourcing_eventstoredb',
    'EVENTSTOREDB_URI': 'localhost:2113',
})

dog_details = school.get_dog(dog_id)

assert dog_details['name'] == 'Fido'
assert dog_details['tricks'] == ['roll over', 'play dead']

For more information, please refer to the Python eventsourcing library and the EventStoreDB project.

Developers

Clone the eventsourcing-eventstoredb repository, set up a virtual environment, and install dependencies.

Use your IDE (e.g. PyCharm) to open the project repository. Create a Poetry virtual environment, and then update packages.

$ make update-packages

Alternatively, use the make install command to create a dedicated Python virtual environment for this project.

$ make install

Start EventStoreDB.

$ make start-eventstoredb

Run tests.

$ make test

Add tests in ./tests. Add code in ./eventsourcing_eventstoredb.

Check the formatting of the code.

$ make lint

Reformat the code.

$ make fmt

Add dependencies in pyproject.toml and then update installed packages.

$ make update-packages

Stop EventStoreDB.

$ make stop-eventstoredb