Publishing Events from the Domain Model

Domain Events should be published when the fact they represent occurs. For instance, when a new user has been registered, a new UserRegistered Event should be published.

Following the newspaper metaphor:

• Modeling a Domain Event is like writing a news article
• Publishing a Domain Event is like printing the article in the paper
• Spreading a Domain Event is like delivering the newspaper so everyone can read the article

The recommended approach for publishing Domain Events is to use a simple Listener-Observer pattern to implement a DomainEventPublisher.

Publishing a Domain Event from an Entity

Continuing with the example of a new user who has been registered in our application, let's see how the corresponding Domain Event can be published:

class User
{
    protected $userId;
    protected $email ;
    protected $password;

    public function __construct(UserId $userId, $email, $password)
    {
        $this->setUserId($userId);
        $this->setEmail($email...