tapahtumalähteisiin

Tapahtumalähteisiin, or event sourcing in English, is an architectural pattern that centers around the idea of storing all changes to application state as a sequence of immutable events. Instead of directly updating a database with the current state, each action or event that modifies the state is recorded as a discrete event. These events are typically stored in an append-only log, often referred to as an event store.

The current state of the application is not stored directly but is derived by replaying the sequence of events from the beginning of the log up to a certain point. This process is known as state reconstruction or state projection. By replaying events, developers can always determine the exact state of the application at any given time.

Key benefits of event sourcing include a complete audit trail of all actions, enabling easier debugging and a clear history of how the system reached its current state. It also facilitates powerful features like temporal queries, allowing users to see what the system looked like at a past point in time. Furthermore, event sourcing can simplify the implementation of complex business logic and support different views of the data by projecting events into various read models. However, it introduces complexity in terms of state reconstruction and requires careful consideration for event schema evolution.