Trait TransactionalEventHandler 

pub trait TransactionalEventHandler:
    Send
    + Sync
    + 'static {
    type Aggregate: Aggregate;

    // Required method
    fn handle(
        &self,
        event: HandledEvent<<Self::Aggregate as Aggregate>::Event>,
        conn: &mut PgConnection,
    ) -> impl Future<Output = Result<()>> + Send;
}

A read-model handler that writes inside the runner’s checkpoint transaction (review C2/LEASE-1).

The runner runs handle and the fenced lease checkpoint in a single Postgres transaction. If this worker has been fenced (a newer leader stole the lease), the checkpoint matches 0 rows and the whole transaction — including the handler’s read-model writes — rolls back. A paused, stale leader therefore cannot land writes the new leader has already moved past, which is the unfenced-handler corruption a plain EventHandler is open to. Net effect: effectively-exactly-once read-model updates for a Postgres sink.

Register with ProjectionRunnerBuilder::subscribe_transactional. Your handle must do all its read-model writes via the supplied conn (e.g. sqlx::query(...).execute(&mut *conn)) — writes on any other connection are not covered by the fence.

Required Associated Types

type Aggregate: Aggregate

Required Methods

fn handle( &self, event: HandledEvent<<Self::Aggregate as Aggregate>::Event>, conn: &mut PgConnection, ) -> impl Future<Output = Result<()>> + Send

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors