DomainEvents

Domain Events represent significant occurrences within a software system's domain. They are immutable facts that describe something that has happened. When a business action takes place, it can trigger the generation of one or more domain events. These events are then typically published and can be subscribed to by various parts of the system or even external systems.

The primary purpose of domain events is to decouple different parts of the system. Instead of one component directly calling methods on another to notify it of a change, it simply publishes an event. Other interested components can then react to this event independently. This promotes a more flexible and maintainable architecture.

Domain events are often used in conjunction with patterns like Domain-Driven Design (DDD) and Event Sourcing. In DDD, they help in modeling the domain and communicating changes between bounded contexts. In Event Sourcing, domain events form the fundamental unit of the event store, representing the complete history of changes to an aggregate.

When designing domain events, it's important to ensure they are named clearly and descriptively, reflecting the business meaning of the occurrence. They should also contain all the necessary data for any interested subscriber to act upon without needing to query the system for more information. This immutability and self-contained nature are key characteristics of effective domain events.