在 MassTransit 中，一個消費者可以消費一種或多種消息
消費者的類型包括：普通消費者，saga，saga 狀态機，路由活動（分布式追蹤），處理器 handlers，工作消費者 job comsumers
public class Program
{
public static async Task Main()
{
var busControl = Bus.Factory.CreateUsingRabbitMq(cfg =>
{
cfg.ReceiveEndpoint("order-service", e =>
{
e.Consumer<SubmitOrderConsumer>();
});
});
}
}
繼承 IConsumer，實現 Consume 方法
class SubmitOrderConsumer :
IConsumer<SubmitOrder>
{
public async Task Consume(ConsumeContext<SubmitOrder> context)
{
await context.Publish<OrderSubmitted>(new
{
context.Message.OrderId
});
}
}
三個原則：
public class Program
{
public static async Task Main()
{
var submitOrderConsumer = new SubmitOrderConsumer();
var busControl = Bus.Factory.CreateUsingRabbitMq(cfg =>
{
cfg.ReceiveEndpoint("order-service", e =>
{
e.Instance(submitOrderConsumer);
});
});
}
}
所有接收到的消息都由一個消費者來實例來處理（請确保這個消費者類是線程安全）
Consumer 每次接收到消息都會 new 一個實例
Handler
public class Program
{
public static async Task Main()
{
var busControl = Bus.Factory.CreateUsingRabbitMq(cfg =>
{
cfg.ReceiveEndpoint("order-service", e =>
{
e.Handler<SubmitOrder>(async context =>
{
await Console.Out.WriteLineAsync($"Submit Order Received: {context.Message.OrderId}");
});
});
});
}
}
通過一個委托 Lambda 方法，來消費消息
Others消息的生産可以通過兩種方式産生：發送和發布
發送的時候需要指定一個具體的地址 DestinationAddress，發布的時候消息會被廣播給所有訂閱了這個消息類型的消費者
基于這兩種規則，消息被定義為：命令 command 和事件 event
可以調用以下對象的 send 方法來發送 command：
public class SubmitOrderConsumer :
IConsumer<SubmitOrder>
{
private readonly IOrderSubmitter _orderSubmitter;
public SubmitOrderConsumer(IOrderSubmitter submitter)
=> _orderSubmitter = submitter;
public async Task Consume(IConsumeContext<SubmitOrder> context)
{
await _orderSubmitter.Process(context.Message);
await context.Send(new StartDelivery(context.Message.OrderId, DateTime.UtcNow));
}
}
public async Task SendOrder(ISendEndpointProvider sendEndpointProvider)
{
var endpoint = await sendEndpointProvider.GetSendEndpoint(_serviceAddress);
await endpoint.Send(new SubmitOrder { OrderId = "123" });
}
在配置文件中指定 map 規則
EndpointConvention.Map<StartDelivery>(new Uri(ConfigurationManager.AppSettings["deliveryServiceQueue"]));
直接發送
public class SubmitOrderConsumer :
IConsumer<SubmitOrder>
{
private readonly IOrderSubmitter _orderSubmitter;
public SubmitOrderConsumer(IOrderSubmitter submitter)
=> _orderSubmitter = submitter;
public async Task Consume(IConsumeContext<SubmitOrder> context)
{
await _orderSubmitter.Process(context.Message);
await context.Send(new StartDelivery(context.Message.OrderId, DateTime.UtcNow));
}
}
可以調用以下對象的 publish 方法來發送 event：
IPublishEndpoint
public async Task NotifyOrderSubmitted(IPublishEndpoint publishEndpoint)
{
await publishEndpoint.Publish<OrderSubmitted>(new
{
OrderId = "27",
OrderDate = DateTime.UtcNow,
});
}
Request-Response 模式讓應用程序之間解耦之後，依然采用同步的方式
public async Task Consume(ConsumeContext<CheckOrderStatus> context)
{
var order = await _orderRepository.Get(context.Message.OrderId);
if (order == null)
throw new InvalidOperationException("Order not found");
await context.RespondAsync<OrderStatusResult>(new
{
OrderId = order.Id,
order.Timestamp,
order.StatusCode,
order.StatusText
});
}
需要處理返回類型 OrderStatusResult，異步方式模拟同步，實際上同樣有消息隊列，消費者處理過程
IClientFactory
public interface IClientFactory
{
IRequestClient<T> CreateRequestClient<T>(ConsumeContext context, Uri destinationAddress, RequestTimeout timeout);
IRequestClient<T> CreateRequestClient<T>(Uri destinationAddress, RequestTimeout timeout);
RequestHandle<T> CreateRequest<T>(T request, Uri destinationAddress, CancellationToken cancellationToken, RequestTimeout timeout);
RequestHandle<T> CreateRequest<T>(ConsumeContext context, T request, Uri destinationAddress, CancellationToken cancellationToken, RequestTimeout timeout);
}
通過 IBusControl 的 CreateClientFactory 方法可以得到 ClientFactory
IRequestClient
public interface IRequestClient<TRequest>
where TRequest : class
{
RequestHandle<TRequest> Create(TRequest request, CancellationToken cancellationToken, RequestTimeout timeout);
Task<Response<T>> GetResponse<T>(TRequest request, CancellationToken cancellationToken, RequestTimeout timeout);
}
RequestClient 可以創建請求，或者直接獲得響應
Send a request
var serviceAddress = new Uri("rabbitmq://localhost/check-order-status");
var client = bus.CreateRequestClient<CheckOrderStatus>(serviceAddress);
var response = await client.GetResponse<OrderStatusResult>(new { OrderId = id});
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