为什么我在自动映射器中出现“缺少类型映射配置或不支持的映射”错误？

Question

代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using AutoMapper;

namespace TestAutomapper
{
  class Program
  {
    static void Main(string[] args)
    {

      var config = new MapperConfiguration(cfg => cfg.CreateMap<MyClassSource, MyClassDestination>());


      var mapper = config.CreateMapper();

      var source = new MyClassSource { DateTimeValue = null };

      var mapped = mapper.Map<MyClassSource, MyClassDestination>(source);
    }

  }

  public class MyClassSource
  {
    public object DateTimeValue { get; set; }
  }

  public class MyClassDestination
  {
    public DateTime? DateTimeValue { get; set; }
  }
}

错误是：

    AutoMapper.AutoMapperMappingException was unhandled
      HResult=-2146233088
      Message=Error mapping types.

    Mapping types:
    MyClassSource -> MyClassDestination
    TestAutomapper.MyClassSource -> TestAutomapper.MyClassDestination

    Type Map configuration:
    MyClassSource -> MyClassDestination
    TestAutomapper.MyClassSource -> TestAutomapper.MyClassDestination

    Property:
    DateTimeValue
      Source=Anonymously Hosted DynamicMethods Assembly
      StackTrace:
           at lambda_method(Closure , MyClassSource , MyClassDestination , ResolutionContext )
           at TestAutomapper.Program.Main(String[] args) in C:\Users\costa\documents\visual studio 2015\Projects\TestAutomapper\TestAutomapper\Program.cs:line 22
           at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
           at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
           at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
           at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
           at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
           at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
           at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
           at System.Threading.ThreadHelper.ThreadStart()
      InnerException: 
           HResult=-2146233088
           Message=Missing type map configuration or unsupported mapping.

    Mapping types:
    Object -> Nullable`1
    System.Object -> System.Nullable`1[[System.DateTime, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]
           Source=Anonymously Hosted DynamicMethods Assembly
           StackTrace:
                at lambda_method(Closure , Object , Nullable`1 , ResolutionContext )
                at lambda_method(Closure , MyClassSource , MyClassDestination , ResolutionContext )
           InnerException: 

我认为这个错误已经解决了 (https://github.com/AutoMapper/AutoMapper/issues/1095)。我正在使用 Automapper 5.1.1。

我该如何解决这个问题？

谢谢

编辑：澄清一下，我关心的是空值的处理。我知道从非空对象值转换为 DateTime 很复杂。在实际代码中，源对象中的实际值为 null 或 DateTime。我认为 null 的处理没有错误。

编辑：

我创建了一个扩展方法 ToDate 来将对象转换为日期，并添加了这个映射来处理从对象到 DateTime 的转换？：

cfg.CreateMap<object, DateTime?>().ConstructUsing(src => src.ToDate());

Answer 1

由于源类型和目标类型中的属性名称相同，AutoMapper 会尝试从对象转换为 DateTime？这是不可能的，这就是您收到您提到的错误的原因。

您需要定义如何解析 DateTime？财产。这将起作用：

var config = new MapperConfiguration(
    cfg =>
    {
        cfg.CreateMap<MyClassSource, MyClassDestination>()
            .ForMember(
                destination => destination.DateTimeValue,
                memberOptions => memberOptions.ResolveUsing(sourceMember =>
                {
                    DateTime dateTime;
                    return !DateTime.TryParse(sourceMember.DateTimeValue.ToString(), out dateTime) ? (DateTime?) null : dateTime;
                }));
    }
);

如果您的源成员是有效的日期时间对象，它将被转换为日期时间，否则目标属性将获得空值。