.NET Core 7.0依赖注入报错：无法解析IRepository服务

问题现象 #

项目启动时触发依赖注入解析失败错误：

System.InvalidOperationException: Unable to resolve service for type 'Marketmax.Common.IRepository`1[Marketmax.Service.Entities.ServiceEntity]' while attempting to activate 'Marketmax.MicroService.Controllers.ServicesController'.

相关代码片段 #

Program.cs配置 #

// Configure services
builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddMongo(configuration); // MongoDB初始化
builder.Services.AddMongoRepository<ServiceEntity>("Services");

// 问题触发点
builder.Services.AddScoped<ServicesController>();

ServicesController实现 #

namespace Marketmax.MicroService.Controllers
{
   [ApiController]
   [Route("services")]
   public class ServicesController : ControllerBase
   {
      private readonly IRepository<ServiceEntity> _repository;

      public ServicesController(IRepository<ServiceEntity> repository)
      {
         _repository = repository;
      }

      // ... 控制器操作方法
   }
}

NuGet包中的IRepository接口 #

public interface IRepository<T> where T : IServiceEntity
{
    Task<IReadOnlyCollection<T>> GetAllAsync();

    Task<IReadOnlyCollection<T>> GetAllAsync(Expression<Func<T, bool>> filter);

    Task CreateAsync(T entity);

    Task<T> GetAsync(Guid id);

    Task<T> GetAsync(Expression<Func<T, bool>> filter);

    Task RemoveAsync(Guid id);

    Task UpdateAsync(T entity);
}

NuGet包中的Mongo扩展方法 #

public static class MongoExtension
{
    public static IServiceCollection AddMongo(this IServiceCollection services, IConfiguration configuration)
    {
        IConfiguration configuration2 = configuration;
        BsonSerializer.RegisterSerializer(new GuidSerializer(BsonType.String));
        BsonSerializer.RegisterSerializer(new DateTimeSerializer(BsonType.String));
        services.AddSingleton(delegate
        {
            ServiceSettings serviceSettings = configuration2.GetSection("ServiceSettings").Get<ServiceSettings>();
            MongoDbSettings mongoDbSettings = configuration2.GetSection("MongoDbSettings").Get<MongoDbSettings>();
            MongoClient mongoClient = new MongoClient(mongoDbSettings.ConnectionString);
            return mongoClient.GetDatabase(serviceSettings.ServiceName);
        });
        return services;
    }

    public static IServiceCollection AddMongoRepository<T>(this IServiceCollection services, string collectionName) where T : IServiceEntity
    {
        string collectionName2 = collectionName;
        services.AddSingleton((Func<IServiceProvider, IRepository<IServiceEntity>>)delegate (IServiceProvider serviceProvider)
        {
            IMongoDatabase service = serviceProvider.GetService<IMongoDatabase>();
            return new MongoRepository<IServiceEntity>(service, collectionName2);
        });
        return services;
    }
}

完整错误栈 #

System.InvalidOperationException: Unable to resolve service for type 'Marketmax.Common.IRepository`1[Marketmax.Service.Entities.ServiceEntity]' while attempting to activate 'Marketmax.MicroService.Controllers.ServicesController'.
   at Microsoft.Extensions.DependencyInjection.ActivatorUtilities.GetService(IServiceProvider sp, Type type, Type requiredBy, Boolean isDefaultParameterRequired)
   at lambda_method9(Closure, IServiceProvider, Object[])
   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.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

问题根源 #

AddMongoRepository<T>方法中注册的是IRepository<IServiceEntity>类型实例，但控制器依赖的是IRepository<ServiceEntity>。由于泛型接口未声明协变（且接口包含输入参数的方法，无法声明协变），DI容器无法将IRepository<IServiceEntity>自动转换为IRepository<ServiceEntity>。

修复方案 #

1. 修改扩展方法注册逻辑 #

调整AddMongoRepository<T>，注册与泛型参数T匹配的IRepository<T>类型：

public static class MongoExtension
{
    // 保留AddMongo方法不变

    public static IServiceCollection AddMongoRepository<T>(this IServiceCollection services, string collectionName) where T : IServiceEntity
    {
        services.AddSingleton<IRepository<T>>(serviceProvider =>
        {
            var database = serviceProvider.GetService<IMongoDatabase>();
            return new MongoRepository<T>(database, collectionName);
        });
        return services;
    }
}

2. 修正MongoRepository实现 #

确保MongoRepository<T>直接实现IRepository<T>，而非IRepository<IServiceEntity>：

public class MongoRepository<T> : IRepository<T> where T : IServiceEntity
{
    private readonly IMongoCollection<T> _collection;

    public MongoRepository(IMongoDatabase database, string collectionName)
    {
        _collection = database.GetCollection<T>(collectionName);
    }

    // 实现IRepository<T>的所有方法...
}

3. 移除冗余控制器注册 #

删除builder.Services.AddScoped<ServicesController>()，因为AddControllers()已经自动完成所有控制器的注册，手动注册可能导致生命周期冲突。

内容的提问来源于stack exchange，提问作者Berlin Johns. M