Event Sourcing

Event sourcing is a state management pattern that records every change as an immutable event in a sequence. This event store provides a complete audit trail and enables temporal queries to reconstruct state at any point in time.

You build an event-sourced aggregate by defining an entity that applies immutable events sequentially from the event store. The provided TypeScript examples demonstrate implementing this order tracking workflow from creation to shipment.

You need snapshotting when loading times for an aggregate become slow due to a long event stream. Snapshots periodically save the materialized state to optimize loading by avoiding replaying the entire event history.

Projections create read models by processing event streams into query-optimized formats. This separates the write model of the event store from the read model, enabling efficient querying without reconstructing aggregate state.

Yes, event sourcing integrates well with CQRS by separating state mutations into an event store while using projections for read models. This combination handles audit trails and complex temporal queries effectively.

A limitation of immutable event sourcing is the overhead of reconstructing state from long event sequences, which requires snapshotting strategies to optimize loading performance and manage event store growth.