NServiceBus buffering saga example

CustomerNotificationHandler.cs

public class CustomerNotificationHandler
	: IHandleMessage<CustomerOrderNotification>
	, IHandleMessage<CustomerOrderStatusNotification>
{
	public IBus Bus {get;set;}

	INotificationService GetClientForCustomer(string customerId)
	{
		return null; // Create a api client for your customer
	}

	public void Handle(CustomerOrderNotification message)
	{
		var service = GetClientForCustomer(message.CustomerId);
		service.Notifiy(message);
		Bus.Reply(new Notified());
	}

	public void Handle(CustomerOrderStatusNotification message)
	{
		var service = GetClientForCustomer(message.CustomerId);
		service.Notifiy(message);
		Bus.Reply(new Notified());
	}
}

CustomerOrderNotificationSaga_Buffer.cs

// Based on saga data for message buffer

public class CustomerOrderNotificationSaga<CustomerOrderNotificationSaga.Data>
	: IAmStartedByMessages<OrderCreated>
	, IHandleMessages<OrderStatusChanged>
{
	protected override void ConfigureHowToFindSaga(SagaPropertyMapper<CustomerOrderNotificationSaga.Data> mapper)
	{
		// Mapping for OrderCreated is not required, as it is started by it.

		mapper.ConfigureMapping<OrderStatusChanged>(message => message.OrderId).ToSaga(sagaData => sagaData.OrderId);
	}

	public void Handle(OrderCreated message)
	{
		Data.OrderId = message.OrderId;

		Bus.Send(new CustomerOrderNotification{
			CustomerId = message.CustomerId,
			OrderId = message.OrderId,
			// Other order info?
		});
	}

	public void Handle(OrderStatusChanged message)
	{
		var instance = new CustomerOrderStatusNotification
		{
			CustomerId = message.CustomerId,
			OrderId = message.OrderId,
			Status = message.Status,
			Version = message.Version, // <-- Provides ordering!
		};

		Notifications.Add(instance);

		Next();
	}

	public void Handle(Notified message)
	{
		Data.OrderNr++; // <-- Increase version
		
		if(Notifications.Count>0)
		{
			Next();
		}
	}

	void Next()
	{
		CustomerOrderStatusNotification instance = notifications
			.OrderBy(x=>x.Version)
			.First();

		if(Data.OrderNr != instance.Version)
		{
			return; // Versions are not equal!
		}

		notifications.Remove(instance);
		Bus.Send(instance);
	}
	
	public class Data
	{
		[Unique]
		public virtual string OrderId {get;set;}
		public virtual ICollection<CustomerOrderStatusNotification> Notifications {get;set;}
		public virtual int OrderNr {get;set;}
	}
} 

CustomerOrderNotificationSaga_OrderFirst.cs

// Based on retry logic

public class CustomerOrderNotificationSaga<CustomerOrderNotificationSaga.Data>
	: IAmStartedByMessages<OrderCreated>
	, IHandleMessages<OrderStatusChanged>
{
	protected override void ConfigureHowToFindSaga(SagaPropertyMapper<CustomerOrderNotificationSaga.Data> mapper)
	{
		// Mapping for OrderCreated is not required, as it is started by it.

		mapper.ConfigureMapping<OrderStatusChanged>(message => message.OrderId).ToSaga(sagaData => sagaData.OrderId);
	}

	public void Handle(OrderCreated message)
	{
		Data.OrderId = message.OrderId;

		Bus.Send(new CustomerOrderNotification{
			CustomerId = message.CustomerId,
			OrderId = message.OrderId,
			// Other order info?
		});
	}

	public void Handle(OrderStatusChanged message)
	{
		if(Data.OrderNr == 0)
		{
			throw new InvalidOperation("Version out of order, order delivery not yet confirmed.");
		}

		var instance = new CustomerOrderStatusNotification
		{
			CustomerId = message.CustomerId,
			OrderId = message.OrderId,
			Status = message.Status,
			Timestamp = message.Timestamp
		};

		Bus.Send(instance);
	}

	public void Handle(Notified message)
	{
		Data.OrderNr++;
	}
	
	public class Data : SagaData
	{
		[Unique]
		public virtual string OrderId {get;set;}
		public virtual int OrderNr {get;set;}
	}
}

CustomerOrderNotificationSaga_Retry.cs

// Based on retry logic

public class CustomerOrderNotificationSaga<CustomerOrderNotificationSaga.Data>
	: IAmStartedByMessages<OrderCreated>
	, IHandleMessages<OrderStatusChanged>
{
	protected override void ConfigureHowToFindSaga(SagaPropertyMapper<CustomerOrderNotificationSaga.Data> mapper)
	{
		// Mapping for OrderCreated is not required, as it is started by it.

		mapper.ConfigureMapping<OrderStatusChanged>(message => message.OrderId).ToSaga(sagaData => sagaData.OrderId);
	}

	public void Handle(OrderCreated message)
	{
		Data.OrderId = message.OrderId;

		Bus.Send(new CustomerOrderNotification{
			CustomerId = message.CustomerId,
			OrderId = message.OrderId,
			// Other order info?
		});
	}

	public void Handle(OrderStatusChanged message)
	{
		if(Data.OrderNr != message.Version)
		{
			throw new InvalidOperation("Version out of order.");
		}

		var instance = new CustomerOrderStatusNotification
		{
			CustomerId = message.CustomerId,
			OrderId = message.OrderId,
			Status = message.Status,
			Version = message.Version, // <-- Provides ordering!
		};

		Bus.Send(instance);
	}

	public void Handle(Notified message)
	{
		Data.OrderNr++;
	}
	
	public class Data : SagaData
	{
		[Unique]
		public virtual bool OrderId {get;set;}
		public virtual int OrderNr {get;set;}
	}
}