.NET 6 API中Autofac依赖注入失败：无法解析IProductService

问题场景 #

在.NET 6中配置Autofac依赖注入后，调用API接口时抛出服务无法解析异常，提示无法找到IProductService的注册实例以激活ProductsController。此前在低版本.NET的Startup类配置方式下可正常运行，现需适配.NET 6的顶级语句模式修复该问题。

定义的Autofac模块 #

public class AutofacBusinessModule:Module
{
  protected override void Load(ContainerBuilder builder)
  {
    builder.RegisterType<ProductManager>().As<IProductService>();
    builder.RegisterType<EfProductDal>().As<IProductDal>();

    builder.RegisterType<CategoryManager>().As<ICategoryService>();
    builder.RegisterType<EfCategoryDal>().As<ICategoryDal>();

    builder.RegisterType<CustomerManager>().As<ICustomerService>();
    builder.RegisterType<EfCustomerDal>().As<ICustomerDal>();

    builder.RegisterType<RegionManager>().As<IRegionService>();
    builder.RegisterType<EfRegionDal>().As<IRegionDal>();

    builder.RegisterType<TerritoryManager>().As<ITerritoryService>();
    builder.RegisterType<EfTerritoryDal>().As<ITerritoryDal>();

    builder.RegisterType<ShipperManager>().As<IShipperService>();
    builder.RegisterType<EfShipperDal>().As<IShipperDal>();

    // 此处存在注册错误：EmployeeManager应映射到IEmployeeService而非IEmployeeDal
    builder.RegisterType<EmployeeManager>().As<IEmployeeDal>();
    builder.RegisterType<EfEmployeeDal>().As<IEmployeeDal>();

    var assembly = System.Reflection.Assembly.GetExecutingAssembly();
    builder.RegisterAssemblyTypes(assembly).AsImplementedInterfaces()
      .EnableInterfaceInterceptors(new ProxyGenerationOptions()
      {
        Selector = new AspectInterceptorSelector()
      }).SingleInstance();
  }
}

API控制器代码 #

[Route("api/[controller]")]
[ApiController]
public class ProductsController : Controller
{
  private readonly IProductService _productService;
  public ProductsController(IProductService productService)
  {
    _productService = productService;
  }

  [HttpGet("getall")]
  public IActionResult GetAllProducts()
  {
    var result = _productService.GetAll();
    if (result.Success)
    {
      return Ok(result);
    }

    return BadRequest(result);
  }
}

原Program.cs配置（未生效） #

IHostBuilder CreateHostBuilder(string[] args) =>
  Host.CreateDefaultBuilder(args)
    .UseServiceProviderFactory(new AutofacServiceProviderFactory())
    .ConfigureContainer<ContainerBuilder>(builder =>
    {
      builder.RegisterModule(new AutofacBusinessModule());
    });

抛出的异常信息 #

System.InvalidOperationException: Unable to resolve service for type 'TAO.Business.Abstract.IProductService' while attempting to activate 'TAO.WebApi.Controllers.ProductsController'.
   at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetService(IServiceProvider sp, Type type, Type requiredBy, Boolean isDefaultParameterRequired)
   at lambda_method3(Closure , IServiceProvider , Object[] )
   at Microsoft.AspNetCore.Mvc.Controllers.ControllerActivatorProvider.<>c__DisplayClass7_0.<CreateActivator>b__0(ControllerContext controllerContext)
   at Microsoft.AspNetCore.Mvc.Controllers.ControllerFactoryProvider.<>c__DisplayClass6_0.<CreateControllerFactory>g__CreateController|0(ControllerContext controllerContext)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)

请求头信息 #

Accept: /
Connection: keep-alive
Host: localhost:7019
User-Agent: PostmanRuntime/7.30.0
Accept-Encoding: gzip, deflate, br
Postman-Token: fbff062e-ca49-4f37-afc5-e8785afbd43c

修复步骤 #

1. 修正Program.cs的Autofac配置方式 #

.NET 6采用顶级语句模式，需通过WebApplication.CreateBuilder生成的builder.Host来配置Autofac，确保配置与Web应用生命周期绑定：

var builder = WebApplication.CreateBuilder(args);

// 配置Autofac作为服务提供工厂
builder.Host.UseServiceProviderFactory(new AutofacServiceProviderFactory());
// 注册自定义Autofac模块
builder.Host.ConfigureContainer<ContainerBuilder>(containerBuilder =>
{
    containerBuilder.RegisterModule(new AutofacBusinessModule());
});

// 添加控制器服务（必须保留，确保控制器被正确发现）
builder.Services.AddControllers();

var app = builder.Build();

// 中间件配置
app.UseHttpsRedirection();
app.UseAuthorization();
app.MapControllers();

app.Run();

2. 修复模块中的注册错误 #

修正EmployeeManager的接口映射错误，避免服务注册冲突：

// 原错误代码
// builder.RegisterType<EmployeeManager>().As<IEmployeeDal>();

// 修正后
builder.RegisterType<EmployeeManager>().As<IEmployeeService>();
builder.RegisterType<EfEmployeeDal>().As<IEmployeeDal>();

3. 解决手动注册与自动注册的冲突 #

模块中同时存在手动注册和程序集自动注册，可能导致生命周期或映射关系冲突：

• 方案一：移除所有手动注册代码，完全依赖程序集扫描（需确保所有服务类都实现了对应接口，且在扫描范围内）
• 方案二：在自动注册时排除已手动注册的类型：

var assembly = System.Reflection.Assembly.GetExecutingAssembly();
builder.RegisterAssemblyTypes(assembly)
       .Where(t => !new[] { nameof(ProductManager), nameof(CategoryManager), nameof(EmployeeManager) }.Contains(t.Name))
       .AsImplementedInterfaces()
       .EnableInterfaceInterceptors(new ProxyGenerationOptions()
       {
         Selector = new AspectInterceptorSelector()
       }).SingleInstance();

4. 确保程序集扫描范围正确 #

如果服务类（如ProductManager）不在WebApi项目程序集中，需指定对应类库的程序集：

// 替换为实际业务层、数据访问层的程序集名称
var businessAssembly = System.Reflection.Assembly.Load("TAO.Business");
var dataAssembly = System.Reflection.Assembly.Load("TAO.DataAccess");

builder.RegisterAssemblyTypes(businessAssembly, dataAssembly)
       .AsImplementedInterfaces()
       .EnableInterfaceInterceptors(new ProxyGenerationOptions()
       {
         Selector = new AspectInterceptorSelector()
       }).SingleInstance();

内容的提问来源于stack exchange，提问作者moongazing