arch-cqrs-es

Model domain state as events by defining aggregates that apply commands to emit append-only events. This approach enables deterministic replay to rebuild state and provides audit trails for domain changes.

Build read-optimized projections by denormalizing event streams into separate read models. This CQRS pattern creates clear boundaries between write models and fast query models for efficient dashboard retrieval.

You need CQRS and event sourcing when requiring separate write and read models with deterministic replay. It suits domains needing audit trails, flexible projections, and complex state modeling like billing systems.

Create an event-sourced domain by defining an aggregate, applying events to mutate state, and projecting reads from the event stream. This establishes an event store with versioning and replay capabilities.

Event sourcing works for billing systems by having writes emit events and reads project current status. This enables flexible read models for dashboards while maintaining an append-only event store audit trail.

CQRS with event sourcing introduces complexity in modeling domain state as events and managing separate read models. It requires handling event store versioning, deterministic replay logic, and building projections for queries.