Domain event

From [[Domain-Driven Design]] ([[DDD]]).

Context

A service often needs to publish events when it updates its data. These events might be needed, for example, to update a CQRS view. Alternatively, the service might participate in an choreography-based saga, which uses events for coordination.

Problem

How does a service publish an event when it updates its data?

Solution

Organize the business logic of a service as a collection of DDD aggregates that emit domain events when they created or updated. The service publishes these domain events so that they can be consumed by other services.

Related patterns

• The [[Saga]] and [[CQRS]] patterns create the need for this pattern

• The [[Aggregate]] pattern is used to structure the business logic

• The [[Transactional outbox]] pattern is used to publish events as part of a database transaction

• [[Event sourcing]] is sometimes used to publish domain events

See also

My book Microservices patterns describes this pattern in a lot more detail.