Playground app modelling candidate simple path in a recruitment process implementing Event Sourcing(ES) Command Query Resposibility Segregation (CQRS) concepts.
Command path is represented by Candidate
aggregate. The aggregate is build on
streams of sequential events, that are persisted (instead of persisting state itself).
Query path is represented by CandidateProjection
read model and is build by
handling Candidate
dispatched events.
Aggregate state is reconstructed from stream of persisted StorageEvent
(Event Sourcing).
Each aggregate modification is manifested by specific type of DomainEvent
dispatch.
However all DomainEvent
types are persisted in the same StorageEvent
structure.
Transformation between DomainEvent
and StorageEvent
is bidirectional and implemented
by EventMapper
class.
LocalEventPublisher
that is a simplified implementation of event bus. There is no message broker, published events are directly passed to event handlers.CandidateProjection
handler method called in use case method (in the same transaction asCandidate
aggregate modification). However it increases coupling betweenCandidate
aggreagte andCandidateProjection
read model.- any implementation of real event bus / message broker (RabbitMQ, Kafka). Thanks to it, read model can be placed in other module / application / system, and update is eventually consistent
Application Architecture is port and adapters.
- secondary ports (interfaces) in application and domain layers
- secondary adapters (implementations) in infrastructure layer
- primary ports (application service and handlers) in application layer
- primary adapter (API for incoming request) is not implemented
The implementation is simplified and omits some important aspects like:
- events versioning
- concurrency version control
- snapshoting of an aggregate
- genuine event bus implementation
- API to transport incoming requests
Huge part of this code was inspired by: https://breadcrumbscollector.tech/category/event-sourcing/
>> pip install -r dev_requirements.txt
>> PYTHONPATH=src pytest -x