esdb-sample.ts

import {
  EventStoreDBClient,
  jsonEvent,
  FORWARDS,
  START,
  JSONEventType,
} from "@eventstore/db-client";

interface Reservation {
  reservationId: string;
  movieId: string;
  userId: string;
  seatId: string;
}

type SeatReservedEvent = JSONEventType<
  "seat-reserved",
  {
    reservationId: string;
    movieId: string;
    userId: string;
    seatId: string;
  }
>;

type SeatChangedEvent = JSONEventType<
  "seat-changed",
  {
    reservationId: string;
    newSeatId: string;
  }
>;

type ReservationEvents = SeatReservedEvent | SeatChangedEvent;

async function main(): Promise<void> {
  try {
    const client = EventStoreDBClient.connectionString("esdb://localhost:2113?tls=false");
    const streamName = "booking-abc123";
    console.log("Creating and appending events...");
    await createAndAppendEvents(client, streamName);
    console.log("Reading and processing events...");
    const reservation = await readAndProcessEvents(client, streamName);
    console.log("Final reservation state:", JSON.stringify(reservation, null, 2));
  } catch (error) {
    console.error('An error occurred:', error);
  }
}

async function createAndAppendEvents(client: EventStoreDBClient, streamName: string): Promise<void> {
  const seatReservedEvent = jsonEvent<SeatReservedEvent>({
    type: "seat-reserved",
    data: {
      reservationId: "abc123",
      movieId: "tt0368226",
      userId: "nm0802995",
      seatId: "4b",
    },
  });

  const seatChangedEvent = jsonEvent<SeatChangedEvent>({
    type: "seat-changed",
    data: {
      reservationId: "abc123",
      newSeatId: "5c",
    },
  });

  await client.appendToStream(streamName, [seatReservedEvent, seatChangedEvent]);
  console.log("Events appended to stream.");
}

async function readAndProcessEvents(client: EventStoreDBClient, streamName: string): Promise<Partial<Reservation>> {
  const events = client.readStream<ReservationEvents>(streamName, {
    fromRevision: START,
    direction: FORWARDS,
    maxCount: 10,
  });

  const reservation: Partial<Reservation> = {};

  for await (const { event } of events) {
    if (!event) continue;

    switch (event.type) {
      case "seat-reserved": {
        console.log("Applying 'seat-reserved' event to reservation state.");
        reservation.reservationId = event.data.reservationId;
        reservation.movieId = event.data.movieId;
        reservation.seatId = event.data.seatId;
        reservation.userId = event.data.userId;
        break;
      }
      case "seat-changed": {
        console.log("Applying 'seat-changed' event to reservation state.");
        reservation.seatId = event.data.newSeatId;
        break;
      }
      default:
        break; 
    }
  }
  return reservation;
}

main().then(() => {
  console.log('Execution completed successfully.');
  process.exit(0); 
}).catch((error) => {
  console.error('An error occurred:', error);
  process.exit(1);
});