advanced~3h
Event Replay and Subscription Queries
Tracking processors were introduced specifically because they make replay possible — this module is replay itself, and its natural companion: subscription queries, which push live updates to a UI as new events land instead of making it poll.
Learning objectives
- Explain why replaying the full event history to rebuild a read model is a capability traditional CRUD systems don't have
- Trigger a reset of a tracking processor's token to replay events for one or more processing groups
- Design a projector's @EventHandler methods to be safely replayable (idempotent with respect to reprocessing)
- Implement an Axon subscription query to push live order summary updates to a client
- Distinguish a subscription query's initial result from its incremental updates and handle both correctly
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Event Replay and Subscription Queries