Event Serialization

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This page is under construction.

By default events are serialized to a plain payload, and deserialized again, using class-transformer. That works for events that only contain primitive values. When an event contains other types, such as Dates or value objects, create an event serializer that converts the event to a payload of plain values and back.

The serializer is a class that implements the IEventSerializer interface and is decorated with @EventSerializer(), which takes the event it serializes.

import {
  Event,
  EventSerializer,
  type IEvent,
  type IEventPayload,
  type IEventSerializer,
} from '@ocoda/event-sourcing';
 
@Event('account-opened')
export class AccountOpenedEvent implements IEvent {
  constructor(
    public readonly accountId: AccountId,
    public readonly openedOn: Date,
    public readonly accountOwnerIds?: AccountOwnerId[],
  ) {}
}
 
@EventSerializer(AccountOpenedEvent)
export class AccountOpenedEventSerializer implements IEventSerializer<AccountOpenedEvent> {
  serialize({ accountId, openedOn, accountOwnerIds }: AccountOpenedEvent): IEventPayload<AccountOpenedEvent> {
    return {
      accountId: accountId.value,
      openedOn: openedOn.toISOString(),
      accountOwnerIds: accountOwnerIds?.map((id) => id.value),
    };
  }
 
  deserialize({ accountId, openedOn, accountOwnerIds }: IEventPayload<AccountOpenedEvent>): AccountOpenedEvent {
    return new AccountOpenedEvent(
      AccountId.from(accountId),
      openedOn && new Date(openedOn),
      accountOwnerIds?.map((id) => AccountOwnerId.from(id)),
    );
  }
}

The keys of the payload that serialize returns are the keys that deserialize receives, so read the same names back (accountId in the example above).

Register the serializer as a provider in one of your modules and it’s used for that event instead of the default one. Serializers are discovered when the application bootstraps, see Module configuration. The event itself still needs to be registered, either in EventSourcingModule.forRoot() or in a feature module with EventSourcingModule.forFeature().

Event Pub/Sub Custom Stores