Overview

The CancelOrderCommand is an integration event published by the Finance service when an order transitions to the Cancelled state. This command is part of the order processing saga and is used to notify other services about order cancellation, particularly for sending cancellation notifications to customers.

Architecture

Message Structure

The command contains the following properties:

Workflow Context

This command is published by the Order State Machine when the following conditions are met:

1. The order is in the Placed state
2. An OrderStatusChangedToCancelIntegrationEvent is received
3. The order transitions to the Cancelled state
4. The customer’s email is available (not null)

Technical Implementation

The CancelOrderCommand is implemented as follows:

[AsyncApi]
[Channel("notification-cancel-order")]
[SubscribeOperation(
    typeof(CancelOrderCommand),
    OperationId = nameof(CancelOrderCommand),
    Summary = "Cancel order notification"
)]
public sealed record CancelOrderCommand(Guid OrderId, string? Email, decimal TotalMoney)
    : IntegrationEvent;

Within the Order State Machine, the command is published during the state transition:

When(OrderCancelled)
    .Then(context =>
    {
        context.Saga.OrderId = context.Message.OrderId;
        context.Saga.BasketId = context.Message.BasketId;
        context.Saga.Email = context.Message.Email;
        context.Saga.TotalMoney = context.Message.TotalMoney;

        logger.LogInformation(
            "[{Event}] Order cancelled for {OrderId}",
            nameof(OrderCancelled),
            context.Message.OrderId
        );
    })
    .TransitionTo(Cancelled)
    .If(
        context => context.Saga.Email is not null,
        x =>
            x.Publish(context => new CancelOrderCommand(
                context.Saga.OrderId,
                context.Saga.Email,
                context.Saga.TotalMoney.GetValueOrDefault(0.0M)
            ))
    )

Consuming Services

This command is typically consumed by:

• Notification Service: To send cancellation emails to customers
• Ordering Service: To update the order status in the database