Architecture
This page shows how the crate’s components connect and where your domain code fits in.
Component Overview
You define: Aggregates, events, commands, projections
The crate provides: Repository orchestration, store abstraction, serialisation
The Envelope Pattern
Events travel with metadata, but domain types stay pure:
- Aggregates receive only the pure event—no IDs or metadata
- Projections receive the full envelope—aggregate ID and metadata included
- Stores persist the envelope but deserialise only what’s needed
This keeps domain logic free of infrastructure concerns.
Command Execution Flow
Projection Loading Flow
Projections define their event filters centrally in the ProjectionFilters trait. The repository calls filters() to determine which events to load, then replays them into the projection.
Key Types
| Type | Role |
|---|---|
Repository | Orchestrates command execution, aggregate loading, and projection loading |
EventStore | Trait for event persistence |
SnapshotStore | Trait for aggregate/projection snapshots |
Aggregate | Trait for command-side entities |
ProjectionFilters | Base trait for event subscribers (projections) |
Projection | Stable KIND identifier for projection snapshot storage |
ApplyProjection<E> | Per-event handler for projections |
Filters | Builder for event filter specs + handler closures |
DomainEvent | Marker trait for event structs |
For exact generic signatures, see the API docs on docs.rs. This page is intentionally focused on responsibilities and flow.
Next
Installation — Add the crate to your project