Building a Domain Events Subject

What happens when we say, aggregate.addDomainEvent(event: IDomainEvent) from an Aggregate?

Here's the base AggregateRoot class that we're using in DDDForum.

// shared/domain/AggregateRoot.ts

import { Entity } from "./Entity"
import { IDomainEvent } from "./events/IDomainEvent"
import { DomainEvents } from "./events/DomainEvents"
import { UniqueEntityID } from "./UniqueEntityID"

export abstract class AggregateRoot<T> extends Entity<T> {
   * All of the domain events for a subclass of AggregateRoot<T>
   * get added to this private array.

  private _domainEvents: IDomainEvent[] = []

  get id(): UniqueEntityID {
    return this._id

  get domainEvents(): IDomainEvent[] {
    return this._domainEvents

   * @method addDomainEvent
   * @protected
   * @desc Called by a subclass in order to add a Domain Event
   * to the list of Domain Events currently on this aggregate
   * within a transactional boundary. Also notifies the DomainEvents
   * subject that the current aggregate has at least one Domain Event
   * that we will need to publish if the transaction completes.

  protected addDomainEvent(domainEvent: IDomainEvent): void {
    // Add the domain event to this aggregate's list of domain events
    // Add this aggregate instance to the domain event's list of aggregates who's
    // events it eventually needs to dispatch.
    // Log the domain event

  public clearEvents(): void {
    this._domainEvents.splice(0, this._domainEvents.length)

  private logDomainEventAdded(domainEvent: IDomainEvent): void {
    const thisClass = Reflect.getPrototypeOf(this)
    const domainEventClass = Reflect.getPrototypeOf(domainEvent)
      `[Domain Event Created]:`,,

So the real magic that happens with this subclass is within the addDomainEvent() method. Not only do we add the IDomainEvent to a list of Domain Events currently on the Aggregate for the transaction, but we notify the DomainEvents subject that the current Aggregate should be marked for dispatch. This means that when the transaction for this Aggregate completes, we should publish the Domain Events attached to the Aggregate

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