c# - 无法使用自动映射器映射内部导航属性。EF 核心

Question

对于该特定问题，我有这样的实体：Album，Photo。每个都Album包含一个s的集合。Photo

和 Dto classes: ，其中AlbumWithPhotosDto包含.PhotoDto

在我的自动映射器配置文件中，我描述了所有实体的映射规则：

CreateMap<Photo, PhotoDto>()
                .ForMember(dest => dest.AverageRate, opt => opt.MapFrom(src => src.Ratings.Average(r => r.Rate)))
                .ForMember(dest => dest.RatesCount, opt => opt.MapFrom(src => src.Ratings.Count))
                .ReverseMap();

 CreateMap<Album, AlbumWithPhotosDto>()
                .ForMember(dest => dest.PhotosNum, opt => opt.MapFrom(src => src.Photos.Count))
                .ReverseMap();

首先LazyLoadingProxies，当我尝试将 an 映射Album到AlbumWithPhotosDto.

我有例外：

错误映射类型。

映射类型：相册 -> AlbumWithPhotosDto DAL.Entities.Album -> BLL.DataTransferObjects.AlbumWithPhotosDto

类型映射配置：Album -> AlbumWithPhotosDto DAL.Entities.Album -> BLL.DataTransferObjects.AlbumWithPhotosDto

目的地成员：照片

然后我改变了显式加载的延迟加载，例如：

_context.Albums
            .Include(a => a.Photos)
            .Include(a => a.Author)

但我又遇到了同样的例外。我该如何解决这个问题？

这里是类的附加定义：

 public class Album : IEntity<int>
    {
        public int Id { get; set; }
        /// <summary>
        /// Album name.
        /// </summary>
        public string Name { get; set; }
        /// <summary>
        /// Album short description.
        /// </summary>
        public string Description { get; set; }
        /// <summary>
        /// Whether the other users can view and rate the album photos or not.
        /// </summary>
        public bool IsPrivate { get; set; }
        /// <summary>
        /// Foreign key, creator's id.
        /// </summary>
        public string AuthorId { get; set; }
        /// <summary>
        /// User who created the album but not obviously author of all photos.
        /// </summary>
        public virtual User Author { get; set; }
        /// <summary>
        /// Photos in album.
        /// </summary>
        public virtual ICollection<Photo> Photos { get; set; } = new HashSet<Photo>();
    }

public class Photo : IEntity<int>
    {
        public int Id { get; set; }
        /// <summary>
        /// Optional photo short description.
        /// </summary>
        public string Description { get; set; }
        /// <summary>
        /// Path to the photo file on the hard drive.
        /// </summary>
        public string FileName { get; set; }
        /// <summary>
        /// Date and time of uploading.
        /// </summary>
        public DateTime UploadDate { get; set; }
        /// <summary>
        /// Photo ratings by users.
        /// </summary>
        public virtual ICollection<Rating> Ratings { get; set; } = new HashSet<Rating>();
        /// <summary>
        /// Foreigh key, author's id.
        /// </summary> 
        public string AuthorId { get; set; }
        public virtual User Author { get; set; }
        public int AlbumId { get; set; }
        public virtual Album Album { get; set; }
    }

public class AlbumWithPhotosDto : IDtoMetadata
    {
        public int Id { get; set; }
        public string Description { get; set; }
        public string AuthorId { get; set; }
        public int PhotosNum { get; set; }
        public ICollection<PhotoDto> Photos { get; set; }
    }

public class PhotoDto : IDtoMetadata
    {
        public int Id { get; set; }
        public string Base64 { get; set; }
        public string Description { get; set; }
        public double AverageRate { get; set; }
        public int RatesCount { get; set; }
        public DateTime UploadDate { get; set; }
        public string AuthorId { get; set; }
        public ICollection<RatingDto> Ratings { get; set; }
    }

标签： c#entity-frameworkasp.net-coreasp.net-web-apiautomapper

Answer 1

您没有Ratings在查询中包含 。因此，AutoMapper 基本上是在尝试调用.Average()一个空集合，因此失败了。

将您的查询修改为 -

var albums = _context.Albums
            .Include(a => a.Photos).ThenInclude(p => p.Ratings)
            .Include(a => a.Author)
            .ToList();