为什么当消费者在 MassTransit RouterSlip 中抛出异常时不调用 Compensate 方法

Question

我在 saga 状态机中构建了一个路由器 slip :

var builder = new RoutingSlipBuilder(NewId.NextGuid());
            var submitOrderUrl = QueueNames.GetActivityUri(nameof(SubmitOrderActivity));
            builder.AddActivity("SubmitOrder", submitOrderUrl, new
            {
                context.Message.OrderId
            });;
            builder.AddActivity("Payment", QueueNames.GetActivityUri(nameof(PaymentActivity)), new {
                context.Message.OrderId,
                context.Message.CustomerId,
                context.Message.Credit
            });
           
            builder.AddActivity("TakeProduct", QueueNames.GetActivityUri(nameof(TakeProductActivity)), new
            {
                context.Message.OrderId,
                Baskets
            });
            builder.AddVariable("OrderId", context.Message.OrderId);
            var routingSlip = builder.Build();
            await context.Execute(routingSlip);

我有 TakeProductActivity activity： public class TakeProductActivity : IActivity: ...

 public async Task<ExecutionResult> Execute(ExecuteContext<TakeProductArgument> context)
        {
            logger.LogInformation($"Take Product Courier called for order {context.Arguments.OrderId}");            
            var uri = QueueNames.GetMessageUri(nameof(TakeProductTransactionMessage));
            var sendEndpoint = await context.GetSendEndpoint(uri);
            await sendEndpoint.Send<TakeProductTransactionMessage>(new
            {
                ProductBaskets = context.Arguments.Baskets                
            });
             
            return context.Completed(new { Baskets = context.Arguments.Baskets, OrderId=context.Arguments.OrderId });
        }

当我使用 sendEndpoint.Send() 方法（即发即弃）时，当服务发生异常时，补偿方法不会自动激活，但是当我使用requestClient.GetResponse(request/reply)方法调用服务时，出现异常时自动调用Compensate方法。在 PaymentConsumer 中，当抛出异常时，必须调用支付补偿方法，但它没有！

///this class has implemented in another micro-service hosted separate process:
public class TakeProductTransactionConsumer : IConsumer<TakeProductTransactionMessage>
....
 public async Task Consume(ConsumeContext<TakeProductTransactionMessage> context)
        {
            if(context.Message.ProductBaskets.Count>0)
             { 
                    throw new Exception("Process Failed!");
             }
            logger.LogInformation($"Take product called ");
         
            Dictionary<int, int> productCounts = new Dictionary<int, int>();
            foreach (var item in context.Message.ProductBaskets)
            {
                productCounts.Add(item.ProductId, item.Count);
            }
            var products = await productService.TakeProducts(productCounts);
            await publishEndpoint.Publish<ProductsUpdatedEvent>(new
            {
                ProductUpdatedEvents = products.Select(p =>new { ProductId = p.Id,p.Price,p.Count}).ToList()
            });
           
            
        }

问题是 MassTransit 无法从 rabbitMQ 获取异常并自动调用补偿方法。当router slip 活动抛出异常时我应该如何告诉MassTransit 调用compensate

Answer 1

如果您的 Take Product activity 使用 Send to fire-and-forget to the take product 服务，并且该服务抛出异常，activity 永远不会知道它，因为它已经完成.即发即弃，在目标服务中没有观察到异常。

如果想在拍品服务抛出异常时拍品activity失败，需要使用request/response从服务中观察异常

为什么当消费者在 MassTransit RouterSlip 中抛出异常时不调用 Compensate 方法

Why Compensate method doesn't Call when a consumer thrown exception in MassTransit RouterSlip

distributed

masstransit

saga

routing-slip