.NET 6中MassTransit与RabbitMQ的IPublishEndpoint依赖注入错误

在.NET 6项目中配置MassTransit集成RabbitMQ后，调用接口时出现无法解析MassTransit.IPublishEndpoint服务以激活ItemsController的异常。项目可正常编译，但访问https://localhost:7234/items接口时触发该错误，更换MassTransit.RabbitMQ版本至7.1.3后问题仍存在。

错误信息 #

fail: Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
      An unhandled exception has occurred while executing the request.
      System.InvalidOperationException: Unable to resolve service for type 'MassTransit.IPublishEndpoint' while attempting to activate 'Play.Catalog.Service.Controllers.ItemsController'.

相关代码 #

Program.cs 代码 #

serviceSettings = configuration.GetSection(nameof(ServiceSettings)).Get<ServiceSettings>();
IServiceCollection services = new ServiceCollection();

services.AddMassTransit(x =>
{
    x.UsingRabbitMq((context, configurator) =>
    {
        var rabbitMQSettings = builder.Configuration.GetSection(nameof(RabbitMQSettings)).Get<RabbitMQSettings>();
        configurator.Host(rabbitMQSettings.Host);
        configurator.ConfigureEndpoints(context, new KebabCaseEndpointNameFormatter(serviceSettings.ServiceName, false));
    });
});

services.AddSingleton<IPublishEndpoint>(provider => provider.GetRequiredService<IBusControl>());

services.AddMassTransitHostedService();

ItemsController.cs 代码 #

[ApiController]
[Route("items")]
public class ItemsController : ControllerBase
{
    private readonly IRepository<Item> itemRepository;
    private readonly IPublishEndpoint publishEndpoint;
    private static int requestCounter = 0;

    public ItemsController(IRepository<Item> itemRepository, IPublishEndpoint publishEndpoint)
    {
        this.publishEndpoint = publishEndpoint;
        this.itemRepository = itemRepository;
    }

    [HttpPost]
    public async Task<ActionResult<ItemDto>> CreateItemAsync(CreateItemDto createItemDto)
    {
        var item = new Item
        {
            Name = createItemDto.Name,
            Description = createItemDto.Description,
            Price = createItemDto.Price,
            CreatedDate = DateTimeOffset.UtcNow
        };
        await itemRepository.CreateItemAsync(item);

        await publishEndpoint.Publish(new CatalogItemCreated(item.Id, item.Name, item.Description));

        return CreatedAtAction(nameof(CreateItemAsync), new { id = item.Id }, item);
    }
}

解决方案 #

问题根源：

• 手动创建独立的ServiceCollection实例，而非使用.NET 6 Web项目默认的builder.Services，导致注册的服务未被应用程序DI容器加载。
• 手动注册IPublishEndpoint属于冗余操作，MassTransit的AddMassTransit方法会自动注册IPublishEndpoint、ISendEndpointProvider等核心服务。

修正步骤：

1. 移除手动创建的IServiceCollection services = new ServiceCollection();，改用项目默认的builder.Services（.NET 6中builder由WebApplication.CreateBuilder(args)生成）。
2. 删除手动注册IPublishEndpoint的代码行：services.AddSingleton<IPublishEndpoint>(provider => provider.GetRequiredService<IBusControl>());。
3. 统一配置对象获取方式，确保使用builder.Configuration而非混用configuration和builder.Configuration。

修正后的Program.cs核心代码：

var builder = WebApplication.CreateBuilder(args);

var serviceSettings = builder.Configuration.GetSection(nameof(ServiceSettings)).Get<ServiceSettings>();

builder.Services.AddMassTransit(x =>
{
    x.UsingRabbitMq((context, configurator) =>
    {
        var rabbitMQSettings = builder.Configuration.GetSection(nameof(RabbitMQSettings)).Get<RabbitMQSettings>();
        configurator.Host(rabbitMQSettings.Host);
        configurator.ConfigureEndpoints(context, new KebabCaseEndpointNameFormatter(serviceSettings.ServiceName, false));
    });
});

builder.Services.AddMassTransitHostedService();

var app = builder.Build();

// 其他中间件配置...

app.Run();

内容的提问来源于stack exchange，提问作者Naman Sharma