Chapter 6. Developing business logic with event sourcing

Mary liked the idea, described in chapter 5, of structuring business logic as a collection of DDD aggregates that publish domain events. She could imagine the use of those events being extremely useful in a microservice architecture. Mary planned to use events to implement choreography-based sagas, which maintain data consistency across services and are described in chapter 4. She also expected to use CQRS views, replicas that support efficient querying that are described in chapter 7.

She was, however, worried that the event publishing logic might be error prone. On one hand, the event publishing logic is reasonably straightforward. Each of an aggregate’s methods that initializes or changes the state of the aggregate returns a list of events. The domain service then publishes those events. But on the other hand, the event publishing logic is bolted on to the business logic. The business logic continues to work even when the developer forgets to publish an event. Mary was concerned that this way of publishing events might be a source of bugs.

6.1. Developing business logic using event sourcing

6.2. Implementing an event store

6.3. Using sagas and event sourcing together

Summary