1

我有以下模型和视图模型（为简洁而编辑）：

public class Advert
{
    public virtual long Id { get; set; }
    public virtual string Title { get; set; }
    public virtual string Descrip { get; set; }
    public virtual IList<AdvertImage> AdvertImages { get; set; }
}

public class AdvertImage
{
    public virtual byte DisplayOrder { get; set; }
    public virtual string Filename { get; set; }
    public virtual string UrlDirectoryRoot { get; set; }
    public virtual long FilesizeBytes { get; set; }

    public virtual Advert Advert { get; set; }
}

public class AdvertImageViewModel
{
    public virtual string Filename { get; set; }
    public virtual byte DisplayOrder { get; set; }
}

public class ListAdvertViewModel
{
    public long Id { get; set; }
    public virtual string Title { get; set; }
    public virtual string Descrip { get; set; }
    public AdvertImageViewModel AdvertImage { get; set; }
}

我有以下 AutoMapper 映射：

Mapper.CreateMap<AdvertImage, AdvertImageViewModel>();

Mapper.CreateMap<Advert, ListAdvertViewModel>()
                .ForMember(d => d.AdvertImage, o => o.MapFrom(s => (s.AdvertImages == null ? null : s.AdvertImages.First())));

然后我的控制器方法之一执行以下操作，以检索 Adverts 列表（其中每个 Advert 可能具有任意数量的 AdvertImages）：

var ads = _advertService.GetAdverts();

然后我尝试将这些广告映射到我的ListAdvertViewModelViewModel 类中

var mappedAds = Mapper.Map<IList<Advert>, IList<ListAdvertViewModel>>(ads);

如果返回的广告之一（在“广告”变量中）有一些要映射的图像，这就会失败。我得到的错误是：

[InvalidOperationException: Sequence contains no elements]
   System.Linq.Enumerable.First(IEnumerable`1 source) +498
   AutoMapper.DelegateBasedResolver`2.Resolve(ResolutionResult source) +153
   System.Linq.Enumerable.Aggregate(IEnumerable`1 source, TAccumulate seed, Func`3 func) +160
   AutoMapper.Mappers.PropertyMapMappingStrategy.MapPropertyValue(ResolutionContext context, IMappingEngineRunner mapper, Object mappedObject, PropertyMap propertyMap) +250

[AutoMapperMappingException: 

Mapping types:
Advert -> AdvertImageViewModel
MyProject.Models.Advert -> MyProject.ViewModels.AdvertImageViewModel

Destination path:
IList`1[1].AdvertImage

我不明白为什么这个 AdvertImage 映射会导致问题？

4

1 回答 1

2

将 First 更改为 FirstOrDefault ，它应该可以工作。

Mapper.CreateMap<Advert, ListAdvertViewModel>()
            .ForMember(d => d.AdvertImage, o => o.MapFrom(s => (s.AdvertImages == null ? null : s.AdvertImages.FirstOrDefault())));
于 2012-06-25T19:21:36.997 回答