c# - AutoMapper .ForMember 用于收集

Question

我有实体 Request 和模型 RequestModel

public class RequestModel : BaseModel
{
    public IEnumerable <int> Recipients { get; set; }
}

public class Request : IIdent
{
    public virtual ICollection <RequestComment> Comments { get; set; }
}

public class RequestComment : IIdent
{
   [ForeignKey("User")]
   public int? UserId { get; set; }
}

我想为 Recipients 创建映射

CreateMap<Request, RequestModel>()
      .ForMember(d => d.Recipients, o => o.MapFrom(s => s.Comments.Select(x => x.UserId )))

但是我遇到了异常:

AutoMapper.AutoMapperMappingException was caught _HResult=-2146233088 HResult=-2146233088 IsTransient=false Message= Mapping types: Request -> IEnumerable1
AttManager.Data.Request -> System.Collections.Generic.IEnumerable1[[System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]] Destination path: RequestModel.Recipients.Recipients Source value: AttManager.Data.Request

Answer 1

当您尝试转换 IEnumerable<RequestComment> 时，问题就来了至 IEnumerable<int> ，所以 Automapper 将尝试找到 RequestComment 之间的转换至 int , 但未定义。

您可以定义从 RequestComment 的转换至 int像这样:

.CreateMap<RequestComment, int>().ConvertUsing(rm => rm.UserId ?? 0);

以及请求模型之间的映射:

.CreateMap<Request, RequestModel>()
.ForMember(d => d.Recipients, o => o.MapFrom(s => s.Comments))

此外，另一种解决问题的方法是定义一个 AfterMap操作:

.CreateMap<Request, RequestModel>()
.AfterMap((r, rm) => rm.Recipients = new List<int>(r.Comments.Select(c => c.UserId ?? 0)));

我只是添加?? 0因为UserId类型是 int? , 所以需要转换为 int对于 Recipients属性(property)。