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Event sourcing and handling

Project description

django-spark - Event sourcing and handling

.. image::

Version |release|

This is not supposed to be real documentation; it's more a reminder for

The idea is that there are event sources and event handlers. Event
sources may create a stream of ``spark.api.Event`` instances, where each
event must have a ``group`` and a ``key``. Additional data may be added
to the ``Event`` as well. Keys are globally unique -- events with the
same key are still only processed exactly once. Groups are used to
determine which handlers handle a certain event.

Event handlers are functions which are called once per
``spark.api.Event`` instance if the event's group matches the event
handler's regex.

Some usage example code

Given a challenge, create events for the challenge (the specifics do not

.. code-block:: python

from datetime import date
from spark import api

def events_from_challenge(challenge):
if not challenge.is_active:

yield api.Event(
key='challenge_created_%s' %,
# Attach any metadata to the Event (it is a types.SimpleNamespace)

if ( - challenge.start_date).days > 2:
if challenge.donations.count() < 2:
yield api.Event(
key='challenge_inactivity_2d_%s' %,

if (challenge.end_date - <= 2:
yield api.Event(
key='challenge_ends_2d_%s' %,

if challenge.end_date <
yield api.Event(
key='challenge_ended_%s' %,

Send mails related to challenges (uses django-authlib's

.. code-block:: python

from import render_to_mail

def send_challenge_mails(event):
# Different mail text per event group:
'challenges/mails/%s' %,
'challenge': event.challenge,

Register the handlers:

.. code-block:: python

class ChallengesConfig(AppConfig):
def ready(self):
# Prevent circular imports:
from spark import api


Challenge = self.get_model('Challenge')

# All this does right now is register a post_save signal
# handler which runs the challenge instance through
# events_from_challenge:

Now, events are generated and handled directly in process.
Alternatively, you might want to handle events outside the
request-response cycle. This can be achieved by only registering the
model event source e.g. in a management command, and then sending all
model instances through all event sources, and directly processing those
events, for example like this:

.. code-block:: python

from spark import api


# Copied from the process_spark_sources management command inside
# this repository
for model, sources in api.MODEL_SOURCES.items():
for instance in model.objects.all():
for source in sources:

- `Documentation <>`_
- `Github <>`_

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