Event Sourcing

[MuhammadKhalilzadeh]

Event Sourcing

Event Sourcing is a pattern where changes to the application state are stored as a sequence of events. Instead of storing the current state, you store the history of events that led to the current state.

Things that we need to consider:

• - Event Store: You need a dedicated database or table to store events. Our PostgreSQL can be used for this purpose, but we may also think about using Redis here as well.
• - Event Schema: Define a schema for events (e.g., event_id, aggregate_metadata, event_type, timestamp, etc).
• - Aggregates: Events are associated with aggregates (e.g., a user, order, etc.). Each aggregate has a unique ID.
• - Event Handlers: Implement handlers to process events and update read models or trigger side effects.
• - Snapshotting: For performance, consider periodically storing snapshots of the aggregate state to avoid replaying too many events.

Implementation in Clean Architecture:

• Infrastructure Layer:

• Implement the event store (e.g., a PostgreSQL table for events).

• Provide repositories for reading/writing events.

• Application Layer:

• Implement event handlers and command handlers that produce events.

• Use a message bus or event dispatcher to publish events.

• Presentation Layer:

• Expose APIs or interfaces to query the current state (read models) or replay events for debugging.