7 MassTransit Saga 模式

╰+攻爆jí腚メ 2022-11-27 12:09 73阅读 0赞

阅读本篇文章前，你应该对CQRS Saga模式有了解

## 定义事件和命令 ##

// 下单命令，用于开启 Saga
    public class PlaceOrderCommand : CorrelatedBy<Guid> 
    { 
        // SagaID，此字段的值将被用来初始化 Saga 的 SagaID
        public Guid CorrelationId {  get; }
    
        public PlaceOrderCommand () { 
            CorrelationId = Guid.NewGuid ();
        }
    }
    
    // 检查库存命令
    public class CheckInStoreCommand : CorrelatedBy<Guid> 
    { 
    public Guid CorrelationId {  get; }
    
        public CheckInStoreCommand (Guid correlationId) { 
            CorrelationId = correlationId;
        }
    }
    
    // 支付完成事件
    public class PayCompletedEnvet : CorrelatedBy<Guid> 
    { 
    public Guid CorrelationId {  get; }
    
        public PayCompletedEnvet (Guid correlationId) { 
            CorrelationId = correlationId;
        }
    }

## 定义Saga ##

// 下单 Saga
    public class PlaceOrderSaga:
        // Saga 接口，必须继承
        ISaga,
        // 用于创建Saga实例的命令
        InitiatedBy<PlaceOrderCommand>,
        // 后续命令
        Orchestrates<CheckInStoreCommand>,
        Orchestrates<PayCompletedEnvet> 
    { 
        // SagaId
        public Guid CorrelationId {  get; set; }
    
        // 处理"下单开始命令"
        public Task Consume (ConsumeContext<PlaceOrderCommand> context) { 
            Console.WriteLine ("下单开始");
            // 发送"检查库存命令"
            context.Publish (new CheckInStoreCommand (context.CorrelationId.Value));
            return Task.CompletedTask;
    }
    
        // 处理"检查库存命令"
        public Task Consume (ConsumeContext<CheckInStoreCommand> context) { 
            Console.WriteLine ("检查库存");
            return Task.CompletedTask;
        }
        
        // 处理"支付完成事件"
        public Task Consume (ConsumeContext<PayCompletedEnvet> context) { 
            Console.WriteLine ("支付完成");
            return Task.CompletedTask;
        }
    }

## 将Saga添加到队列 ##

// 创建基于内存的总线
    var bus = Bus.Factory.CreateUsingInMemory (config => { 
        // 设置接收队列，队列名 test_queue
        config.ReceiveEndpoint ("test_queue", ep => { 
            // 添加 Saga PlaceOrderSaga
            // 使用内存仓库持久化Saga
            ep.Saga<PlaceOrderSaga> (new InMemorySagaRepository<PlaceOrderSaga> ());
        });
    });
    
    bus.Start ();
    
    // 发布下单开始命令
    bus.Publish (new PlaceOrderCommand ()).Wait ();
    
    bus.Stop ();