outbox

Overview ¶

Example: outbox

Demonstrates the transactional outbox pattern with drel.Engine.UseOutbox. Domain events recorded during a business transaction are written to an outbox table *in the same transaction* as the data changes that produced them. This gives a reliable, exactly-once hand-off to external systems (a CDC pipeline like Debezium, a message bus, or a polling relay) without dual-write races: either the order AND its event commit together, or neither does.

Key concepts shown:

• UseOutbox: register an outbox table; every SaveChanges persists the pending domain events into it within the same transaction.
• Atomicity: when a transaction rolls back, no outbox row is left behind — you never publish an event for work that didn't commit.
• Relay: drel.NewRelay claims a batch under a lease, publishes it, and stamps processed_at. A second poll returns nothing. The lease lets more than one replica poll one table, and partition_key keeps the events of one order in order.

Runs against in-memory SQLite (pure-Go modernc.org/sqlite, no CGO and no external database needed).

Usage:

cd examples/outbox
go run ../../cmd/drel generate   # generates orders/order_drel.go + db/drel_gen.go
go run .