某些服务无法在 ASP.NET 核心中构建

Question

由于这个异常，在使用 CQRS 时遇到了困难。我有一个 Movie 模型和 MovieDTO 模型

//EDIT 好的，我刚刚意识到在 GetMoviesQuery 中我不使用 IRepository< MovieDTO >，当我将 MovieRepository 更改为 IRepository<MovieDTO> 时它起作用了

IRepository.cs

public interface IRepository<TEntity>
{
    IEnumerable<TEntity> GetAll();

    TEntity Get(int id);

    TEntity Save(TEntity entity);

    void Delete(int entityId);
}

MovieRepository.cs

public class MovieRepository : IRepository<MovieDTO>
{
    private MyContext _context;
    private IMapper _mapper;
    public MovieRepository(MyContext context)
    {
        _context = context;
        var config = new MapperConfiguration(cfg => {
            cfg.CreateMap<Movie, MovieDTO>();
        });
        _mapper = config.CreateMapper();
    }

    public IEnumerable<MovieDTO> GetAll()
    {
        return _context.Movies.ToList().Select(movie => _mapper.Map<Movie, MovieDTO>(movie));
    }
}

GetMoviesQuery.cs

public class GetMoviesQuery
{
    public class Query : IRequest<IEnumerable<MovieDTO>> { }

    public class Handler : RequestHandler<Query, IEnumerable<MovieDTO>>
    {
        private MovieRepository _repository;

        public Handler(MovieRepository repository)
        {
            _repository = repository ?? throw new ArgumentNullException(nameof(_repository)); 
        }

        protected override IEnumerable<MovieDTO> Handle(Query request)
        {
            return _repository.GetAll();
        }
    }
}

Startup.cs

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllersWithViews();
        services.AddRazorPages();
        services.AddTransient<IRepository<MovieDTO>, MovieRepository>();
        services.AddHttpClient();
        services.AddDbContext<MyContext>(options => options.UseSqlite("Data Source = blogging.db"));
        services.AddMediatR(typeof(Startup));
    }

异常： System.AggregateException: '无法构建某些服务（验证服务描述符 'ServiceType: MediatR.IRequestHandler2[TicketReservationSystem.Server.CQRS.Queries.GetMoviesQuery+Query,System.Collections.Generic.IEnumerable1[TicketReservationSystem.Server.Models.DTO.MovieDTO]] Lifetime: Transient ImplementationType: TicketReservationSystem.Server.CQRS.Queries.GetMoviesQuery+Handler' 时出错：尝试激活

时无法解析类型 'TicketReservationSystem.Server.Data.Repository.MovieRepository' 的服务

我不知道如何真正找出问题所在。

Answer 1

public Handler(MovieRepository repository)

应该改为

public Handler(IRepository<MovieDTO> repository)，因为您使用接口而不是实现注册了容器。

services.AddTransient<IRepository<MovieDTO>, MovieRepository>();

如果您想使用您的原始代码，请注册 class 本身

services.AddTransient<MovieRepository>();

Answer 2

如果您有实现接口，请将其添加到 Startup.cs

public void ConfigureServices(IServiceCollection services)
    { 
      services.AddScoped<IDepartments, Departments>()
    }

某些服务无法在 ASP.NET 核心中构建

Some services are not able to be constructed in ASP.NET Core

c#

repository-pattern

mediatr

asp.net-core