This sample shows a client/server scenario using saga and outbox persistence to store records atomically by leveraging transactions.
Prerequisites
The sample uses a DynamoDB local instance by default. See the AWS guidance on deploying DynamoDB local.
Alternatively with Docker installed locally, execute the following command in the solution directory:
docker-compose up -d
the data is only kept in memory and will be gone when the container is removed. It is possible to inspect the data written to DynamoDB by using the NoSQL Workbench for DynamoDB. The below screenshot shows the PK and SK created for the not yet completed Saga, the outbox entries and the transactionally inserted OrderShippingInformation.
Projects
Client
- Sends the
StartOrdermessage toServer. - Receives and handles the
OrderCompletedevent.
Server projects
- Receive the
StartOrdermessage and initiate anOrderSaga. OrderSagarequests a timeout with an instance ofCompleteOrderwith the saga data.- Receive the
OrderShippedmessage with a custom header. OrderSagapublishes anOrderCompletedevent when theCompleteOrdertimeout fires.
SharedMessages
Contains the shared message contracts used by all endpoints.
Persistence config
Configure the endpoint to use DynamoDB Persistence.
var amazonDynamoDbClient = new AmazonDynamoDBClient(
new BasicAWSCredentials("localdb", "localdb"),
new AmazonDynamoDBConfig
{
ServiceURL = "http://localhost:8000"
});
var endpointConfiguration = new EndpointConfiguration("Samples.DynamoDB.Transactions.Server");
endpointConfiguration.UseSerialization<SystemJsonSerializer>();
var persistence = endpointConfiguration.UsePersistence<DynamoPersistence>();
persistence.DynamoClient(amazonDynamoDbClient);
persistence.UseSharedTable(new TableConfiguration
{
TableName = "Samples.DynamoDB.Transactions"
});
endpointConfiguration.EnableOutbox();
The handler also creates OrderShippingInformation by participating in the transactional batch provided by NServiceBus.
var orderShippingInformation = new OrderShippingInformation
{
Id = Guid.NewGuid(),
OrderId = message.OrderId,
ShippedAt = DateTimeOffset.UtcNow,
};
var session = context.SynchronizedStorageSession.DynamoPersistenceSession();
session.Add(new TransactWriteItem
{
Put = new Put
{
TableName = "Samples.DynamoDB.Transactions",
Item = orderShippingInformation.ToMap()
}
});
Order saga data
public class OrderSagaData :
ContainSagaData
{
public Guid OrderId { get; set; }
public string OrderDescription { get; set; }
}
Order saga
public class OrderSaga :
Saga<OrderSagaData>,
IAmStartedByMessages<StartOrder>,
IHandleMessages<OrderShipped>,
IHandleTimeouts<CompleteOrder>
{
static readonly ILog Log = LogManager.GetLogger<OrderSaga>();
protected override void ConfigureHowToFindSaga(SagaPropertyMapper<OrderSagaData> mapper)
{
mapper.MapSaga(saga => saga.OrderId)
.ToMessage<StartOrder>(msg => msg.OrderId)
.ToMessage<OrderShipped>(msg => msg.OrderId);
}
public async Task Handle(StartOrder message, IMessageHandlerContext context)
{
var orderDescription = $"The saga for order {message.OrderId}";
Data.OrderDescription = orderDescription;
Log.Info($"Received StartOrder message {Data.OrderId}. Starting Saga");
var shipOrder = new ShipOrder
{
OrderId = message.OrderId
};
Log.Info("Order will complete in 5 seconds");
var timeoutData = new CompleteOrder
{
OrderDescription = orderDescription,
OrderId = Data.OrderId,
};
await Task.WhenAll(
context.SendLocal(shipOrder),
RequestTimeout(context, TimeSpan.FromSeconds(5), timeoutData)
);
}
public Task Handle(OrderShipped message, IMessageHandlerContext context)
{
Log.Info($"Order with OrderId {Data.OrderId} shipped on {message.ShippingDate}");
return Task.CompletedTask;
}
public async Task Timeout(CompleteOrder state, IMessageHandlerContext context)
{
Log.Info($"Saga with OrderId {Data.OrderId} completed");
MarkAsComplete();
var orderCompleted = new OrderCompleted
{
OrderId = Data.OrderId
};
await context.Publish(orderCompleted);
}
}