Event Sourcing in Python with MongoDB

This is an extension package for the Python eventsourcing library that provides a persistence module for MongoDB.

Installation

Use pip to install the stable distribution from the Python Package Index. Please note, it is recommended to install Python packages into a Python virtual environment.

$ pip install eventsourcing-mongodb

Getting started

Define Aggregates and Applications the usual way. Please refer to the Eventsourcing Documentation for more detailed examples.

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

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

    @event('TrickAdded')
    def add_trick(self, trick: str):
        self.tricks.append(trick)
    
class DogSchool(Application):
    def register_dog(self, name: str) -> UUID:
        dog = Dog(name)
        self.save(dog)
        return dog.id

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

    def get_dog(self, dog_id: UUID) -> dict:
        dog = self.repository.get(dog_id)
        return {'id': dog.id, 'name': dog.name, 'tricks': dog.tricks}

To configure your Application for using MongoDB for persistence, you need to set the environment variable PERSISTENCE_MODULE to 'eventsourcing_mongodb'. Furthermore, you need to set the environment variables MONGO_CONNECTION_STRING and MONGO_DB_NAME. Please refer to the MongoDB Documentation to learn more about connection strings. You can read more about the available variables here .

import os
os.environ['PERSISTENCE_MODULE'] = 'eventsourcing_mongodb'
os.environ['MONGO_CONNECTION_STRING'] = 'mongodb://localhost'
os.environ['MONGO_DB_NAME'] = 'EventSourcing'

Instead of setting the variables on environment level, you can also set them on application level.

class DogSchool(Application):
    env = {
        'PERSISTENCE_MODULE': 'eventsourcing_mongodb',
        'MONGO_CONNECTION_STRING': 'mongodb://localhost',
        'MONGO_DB_NAME': 'EventSourcing',
        ...
    }
    ...

Construct and use the application in the usual way.

dog_school = DogSchool()
dog_id = dog_school.register_dog('Fido')
dog_school.add_trick(dog_id, 'roll over')
dog = dog_school.get_dog(dog_id)
print(dog) # {'id': UUID('...'), 'name': 'Fido', 'tricks': ['roll over']}

And retrieve the data later:

dog_school = DogSchool()
dog_id = UUID('...')
dog = dog_school.get_dog(dog_id)
print(dog) # {'id': UUID('...'), 'name': 'Fido', 'tricks': ['roll over']}

Available Environment Variables

You can use the following variables to configure mongodb persistence:

Variable	Type / Possible values	Required	Description
PERSISTENCE_MODULE	'eventsourcing_mongodb'	true	configures the application to use this module for persistence.
MONGO_CONNECTION_STRING	string	true	MongoDB Connection String. Please refer to the MongoDB Documentation to learn more about connection strings.
MONGO_DB_NAME	string	true	Name of the Database the data sould be stored in
MONGO_COL_PREFIX	string	false	Prefix for the MongoDB Collections for events, snapshots and trackings. The default is an empty String.