Event Sourcing: Validate, Append, Rebuild State, Publish

Instead of storing the current state, event sourcing stores every change as an immutable event. This workflow validates the incoming event, appends it to the event store (version 5), rebuilds the aggregate state from the full event history (balance: 1500, status: "active"), and publishes the event to subscribers.

Workflow

aggregateId, eventType, eventData
               |
               v
+-----------------------+     +---------------------+     +-----------------------+     +---------------------+
| es_validate_event     | --> | es_append_event     | --> | es_rebuild_state      | --> | es_publish_event    |
+-----------------------+     +---------------------+     +-----------------------+     +---------------------+
  validatedEvent with          eventId generated           state rebuilt from            published: true
  type + data + timestamp      version: 5                  5 events: balance=1500
                               appended: true              status="active"

Workers

ValidateEventWorker -- Validates eventType for aggregateId. Returns validatedEvent containing type, data, and timestamp.

AppendEventWorker -- Appends the event to the store. Returns a generated eventId, version: 5, appended: true.

RebuildStateWorker -- Replays events to rebuild state. Returns state: {balance: 1500, status: "active"} from version events.

PublishEventWorker -- Publishes the event to subscribers. Returns published: true.

Tests

8 unit tests cover event validation, appending, state rebuild, and publishing.

Running

See ../../RUNNING.md for setup and execution instructions.