Domain Event

Definition

An event is something that has happened in the past. A domain event is, something that happened in the domain that you want other parts of the same domain (in-process) to be aware of. The notified parts usually react somehow to the events.

Source: Domain events: design and implementation

Example

Model

Code

public class SubscriptionPaymentCreatedDomainEvent : DomainEventBase
{
    public SubscriptionPaymentCreatedDomainEvent(
        Guid subscriptionPaymentId,
        Guid payerId,
        string subscriptionPeriodCode,
        string countryCode,
        string status,
        decimal value,
        string currency)
    {
        SubscriptionPaymentId = subscriptionPaymentId;
        PayerId = payerId;
        SubscriptionPeriodCode = subscriptionPeriodCode;
        CountryCode = countryCode;
        Status = status;
        Value = value;
        Currency = currency;
    }

    public Guid SubscriptionPaymentId { get; }
    public Guid PayerId { get; }
    public string SubscriptionPeriodCode { get; }
    public string CountryCode { get; }
    public string Status { get; }
    public decimal Value { get; }
    public string Currency { get; }
}

public class DomainEventBase : IDomainEvent
{
    public Guid Id { get; }
    public DateTime OccurredOn { get; }

    public DomainEventBase()
    {
        this.Id = Guid.NewGuid();
        this.OccurredOn = DateTime.UtcNow;
    }
}

Description

A SubscriptionPaymentCreatedDomainEvent gets fired within the SubscriptionPayment aggregate root. This happens whenever a Member who is also a Payer, issues a command to buy a Subscription.

All properties are get only, because an event is something that has happened in the past, and you can not change the past.

Event details:

• SubscriptionPaymentId - Auto generated unique Id for the subscription payment.
• PayerId - The Id of the payer wanting to buy a subscription.
• SubscriptionPeriodCode - The period of validity for this subscription:
  • 1 Month
  • 6 Months
  • Custom
• CountryCode - The code of the country that the payer is issuing from.
• Status - Automatically set to WaitingForPayment.
• Value - The amount to be paid for the chosen subscription period.
• Currecy - The currency of choice of the payer.

Business domain events extend DomainEventBase which in-turn implements the IDomainEvent interface.

Base event details:

• Id - Auto generated unique Id for the event itself.
• OccurredOn - The point-in-time when the event happened.