@effit/event-sourcing

Event sourcing primitives for the Effit framework.

Backend-agnostic core (Aggregate, State, Event, evolve, EventStore) plus a PostgreSQL adapter under @effit/event-sourcing/postgresql/* that wires Emmett (event store) and Pongo (projection store).

Installation

pnpm add @effit/event-sourcing @effit/core effect \
  @event-driven-io/emmett @event-driven-io/emmett-postgresql @event-driven-io/dumbo pg

Defining an aggregate

import { Id } from '@effit/core/Id.js';
import { EventSourcing } from '@effit/event-sourcing/EventSourcing.js';
import { evolve } from '@effit/event-sourcing/evolve.js';
import { Schema } from 'effect';

export const RoundId = Id.create('RoundId');

const UnregisteredRound = EventSourcing.State('UNREGISTERED', {
  id: Schema.tag(RoundId.EMPTY),
});
const PendingRound = EventSourcing.State('PENDING', {
  id: RoundId,
  name: Schema.NonEmptyString,
});

type Round = typeof UnregisteredRound.Type | typeof PendingRound.Type;

const RoundRegistered = EventSourcing.Event('RoundRegistered', {
  roundId: RoundId,
  name: Schema.NonEmptyString,
});

type RoundEvent = typeof RoundRegistered.Type;

export const Round = EventSourcing.Aggregate<RoundId, Round, RoundEvent>(
  'Round',
  {
    idSchema: RoundId,
    eventSchema: RoundRegistered,
    initialState: () => UnregisteredRound.make(),
    evolve: evolve<Round, RoundEvent>()({
      UNREGISTERED: {
        RoundRegistered: (_state, data) =>
          PendingRound.make({ id: data.roundId, name: data.name }),
      },
      PENDING: {},
    }),
  },
);

Reading and writing events

import { Effect } from 'effect';
import { EventStore } from '@effit/event-sourcing/EventStore.js';

const program = Effect.gen(function* () {
  const store = (yield* EventStore).for(Round.Aggregate);

  yield* store.create(roundId, RoundRegistered.make({ /* ... */ }));
  const state = yield* store.getById(roundId);
  yield* store.handle(roundId, (state) => /* ...next event... */);
});

PostgreSQL adapter

Provide EmmettConfig and EmmettEventStoreLive from @effit/event-sourcing/postgresql/* to back EventStore with Emmett + Pongo. EventProjector.SingleStream / .MultiStream define projections, EventReactor defines reactors, EventConsumer composes them, and ConsumerRunner.scoped(consumers) runs the consumer process.

License

MIT © Talysson de Oliveira Cassiano