Introduction
sourcery provides building blocks for pragmatic event-sourced systems in Rust. It keeps your domain types pure while giving you tools to rebuild state, project read models, and persist events through a pluggable store interface.
When to Use Event Sourcing
Event sourcing shines when you need:
- Complete audit trails — every state change is recorded
- Time travel — reconstruct state at any point in history
- Decoupled read models — optimize queries independently of writes
- Complex domain logic — model behavior as a sequence of facts
It adds complexity, so consider simpler approaches for CRUD-heavy applications with minimal business logic.
What This Crate Provides
| Included | Not Included |
|---|---|
| Core traits for aggregates, events, projections | Command bus / message broker |
| Derive macro to reduce boilerplate | Outbox pattern |
| Repository for command execution | Snapshot scheduler |
| In-memory store for testing | Event streaming infrastructure |
| PostgreSQL store (optional) | |
| Test framework (given-when-then) |
The crate is intentionally minimal. You wire the repository into whichever pipeline you prefer—whether that’s a web framework, actor system, or CLI tool.
A Taste of the API
#[derive(Aggregate)]
#[aggregate(id = String, error = String, events(FundsDeposited, FundsWithdrawn))]
pub struct Account {
balance: i64,
}
impl Handle<Deposit> for Account {
fn handle(&self, cmd: &Deposit) -> Result<Vec<Self::Event>, Self::Error> {
Ok(vec![FundsDeposited { amount: cmd.amount }.into()])
}
}The derive macro generates the event enum and serialization glue. You focus on domain behavior.
Next Steps
- Event Sourcing Primer — understand the core concepts
- Quick Start — build your first aggregate in 5 minutes
- Core Traits — deep dive into the API