如何为请求客户端解决MassTransit Mediator“无法构建某些服务”

如何解决如何为请求客户端解决MassTransit Mediator“无法构建某些服务”

我正在查看 Masstransit，我使用 Masstransit dotnet 模板生成了一个工作线程，按照 https://masstransit-project.com/getting-started/（直到 RabbitMQ 的所有内容）

然后我对让内置中介处理响应很感兴趣，因此根据 https://masstransit-project.com/articles/mediator.html

更改了代码

所以它的设置看起来像......

 Host.CreateDefaultBuilder(args)
                .ConfigureServices((hostContext,services) =>
                {
                    services.AddMediator(x =>
                    {
                        x.AddConsumer<MessageConsumer>();
                        x.AddRequestClient<Message>();
                    });
                    services.AddMasstransit(x =>
                    {
                        x.AddConsumersFromNamespaceContaining<MessageConsumer>();

                        x.UsingInMemory((context,cfg) =>
                        {
                            cfg.ConfigureEndpoints(context);
                        });
                    });
                    services.AddMasstransitHostedService(true);
                    
                    services.AddHostedService<Worker>();
                });

消费者/合约现在看起来像

public class Message { public string Text { get; set; } }
public class MessageResult { public string Text { get; set; } }
public class MessageConsumer : IConsumer<Message>
{
    readonly ILogger<MessageConsumer> _logger;

    public MessageConsumer(ILogger<MessageConsumer> logger)
    {
        _logger = logger;
    }

    public Task Consume(ConsumeContext<Message> context)
    {
        _logger.Loginformation("Received Text: {Text}",context.Message.Text);
        return context.RespondAsync(new MessageResult() {Text = $"Got {context.Message.Text}"});
    }
}

工人看起来像

  public class Worker : BackgroundService
    {
        private readonly ILogger<Worker> _logger;
        private readonly IBus _bus;
        private readonly IRequestClient<Message> _request;

        public Worker(ILogger<Worker> logger,IBus bus,IRequestClient<Message> request)
        {
            _logger = logger;
            _bus = bus;
            _request = request;
        }

        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
        {
            while (!stoppingToken.IsCancellationRequested)
            {
                var response = await _request.GetResponse<MessageResult>(new Message {Text = $"The time is {DateTimeOffset.Now}"},stoppingToken);
                await Task.Delay(1000,stoppingToken);
            }
        }
    }

但是，当我运行它时，IRequestClient 的注入似乎失败了（由于某种原因它没有注册？），但有异常

Error while validating the service descriptor 'ServiceType: Microsoft.Extensions.Hosting.IHostedService Lifetime: Singleton ImplementationType: MTGettingStarted.Worker': Cannot consume scoped service 'Masstransit.IRequestClient`1[MTGettingStarted.Message]' from singleton 'Microsoft.Extensions.Hosting.IHostedService'.

我认为 x.AddRequestClient<Message>(); 应该这样做。也许文档不完整？还是我错过了什么？

如果我将工作人员更改为手动获取请求，那么它确实有效

        var client = _mediator.CreateRequestClient<Message>();
        var response = await client.GetResponse<MessageResult>(new Message {Text = $"The time is {DateTimeOffset.Now}"},stoppingToken);

但仍然好奇为什么 DI 不起作用？

解决方法

IRequestClient<T> 在容器中注册为作用域，您发布的错误表明：

Cannot consume scoped service

您的托管服务是单例。