✉️ Messages

Event Sourcing integrates very well with event-driven architectures. In a traditional architecture, you would need to design your system events (or messages for clarity) separately from your data. With Event Sourcing, they can simply broadcast the business events you already designed.

In Castore, we distinguish three types of message:

• AggregateExists messages which only carry aggregate ids (mainly for maintenance purposes)
• Notification messages which also carry event details
• State-carrying messages which also carry their corresponding aggregates

In Castore, they are implemented by the AggregateExistsMessage, NotificationMessage and StateCarryingMessage TS types:

// AggregateExistsMessage
import type {
  AggregateExistsMessage,
  EventStoreAggregateExistsMessage,
} from '@castore/core';

type PokemonAggregateExistsMessage = AggregateExistsMessage<'POKEMONS'>;

// 👇 Equivalent to:
type PokemonAggregateExistsMessage = {
  eventStoreId: 'POKEMONS';
  aggregateId: string;
};

// // 👇 Also equivalent to:
type PokemonAggregateExistsMessage = EventStoreAggregateExistsMessage<
  typeof pokemonsEventStore
>;

// NotificationMessage
import type {
  NotificationMessage,
  EventStoreNotificationMessage,
} from '@castore/core';

type PokemonEventNotificationMessage = NotificationMessage<
  'POKEMONS',
  PokemonEventDetails
>;

// 👇 Equivalent to:
type PokemonEventNotificationMessage = {
  eventStoreId: 'POKEMONS';
  event: PokemonEventDetails;
};

// 👇 Also equivalent to:
type PokemonEventNotificationMessage = EventStoreNotificationMessage<
  typeof pokemonsEventStore
>;

// StateCarryingMessage
import type {
  StateCarryingMessage,
  EventStoreStateCarryingMessage,
} from '@castore/core';

type PokemonEventStateCarryingMessage = StateCarryingMessage<
  'POKEMONS',
  PokemonEventDetails,
  PokemonAggregate
>;

// 👇 Equivalent to:
type PokemonEventStateCarryingMessage = {
  eventStoreId: 'POKEMONS';
  event: PokemonEventDetails;
  aggregate: PokemonAggregate
};

// 👇 Also equivalent to:
type PokemonEventStateCarryingMessage = EventStoreStateCarryingMessage<
  typeof pokemonsEventStore
>;

All types of message can be published through message channels, i.e. Message Queues or Message Buses.