自动映射到接口:"TypeLoadException"异常

Question

我正在研究一个使用Inversion of Control的MVC应用程序,因此广泛使用了接口类型,具体实现由依赖解析器根据需要注入.实体接口继承自描述实体的一些基本管理功能的基本接口.ViewModels也被广泛使用.

该应用程序使用Automapper,我已经创建了从视图模型到各种实体接口的映射.映射配置正确验证.但是,当我调用Automapper执行映射时,代码失败了TypeLoadException.

我相信Automapper能够映射接口(见本吉米博加德).

似乎Automapper代理生成器可能已省略将MyMethod()添加到代理,这会在Reflection尝试创建类型时导致异常.

如果不是这样,我该如何让这张地图发挥作用？我错过了一些明显的事吗？

这是一个简化的控制台应用程序,用于演示场景,并在运行时重现错误:

public interface IEntity
{
    string Foo { get; set; }
    string Bar { get; set; }
    string MyMethod();
}

public class MyEntity : IEntity
{
    public string Foo { get; set; }
    public string Bar { get; set; }
    public string MyMethod()
    {
        throw new NotImplementedException();
    }
}

public class MyViewModel
{
    public string Foo { get; set; }
    public string Bar { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        AutomapperConfig();
        MyViewModel vm = new MyViewModel { Foo = "Hello", Bar = "World" };
        IEntity e = Mapper.Map<MyViewModel, IEntity>(vm);
        Console.WriteLine(string.Format("{0} {1}", e.Foo, e.Bar));
    }

    private static void AutomapperConfig()
    {
        Mapper.Initialize(cfg => {
            cfg.CreateMap<MyViewModel, IEntity>();
        });
        Mapper.AssertConfigurationIsValid();
    }
}

抛出的异常是:

InnerException: System.TypeLoadException
   HResult=-2146233054
   Message=Method 'MyMethod' in type 'Proxy<AutomapperException.IEntity_AutomapperException_Version=1.0.0.0_Culture=neutral_PublicKeyToken=null>' from assembly 'AutoMapper.Proxies, Version=0.0.0.0, Culture=neutral, PublicKeyToken=be96cd2c38ef1005' does not have an implementation.
   Source=mscorlib
   TypeName=Proxy<AutomapperException.IEntity_AutomapperException_Version=1.0.0.0_Culture=neutral_PublicKeyToken=null>
   StackTrace:
        at System.Reflection.Emit.TypeBuilder.TermCreateClass(RuntimeModule module, Int32 tk, ObjectHandleOnStack type)
        at System.Reflection.Emit.TypeBuilder.CreateTypeNoLock()
        at System.Reflection.Emit.TypeBuilder.CreateType()
        at AutoMapper.Impl.ProxyGenerator.CreateProxyType(Type interfaceType)
        at AutoMapper.Impl.ProxyGenerator.GetProxyType(Type interfaceType)
        at AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.CreateObject(ResolutionContext context)
        at AutoMapper.Mappers.TypeMapObjectMapperRegistry.NewObjectPropertyMapMappingStrategy.GetMappedObject(ResolutionContext context, IMappingEngineRunner mapper)
        at AutoMapper.Mappers.TypeMapObjectMapperRegistry.PropertyMapMappingStrategy.Map(ResolutionContext context, IMappingEngineRunner mapper)
        at AutoMapper.Mappers.TypeMapMapper.Map(ResolutionContext context, IMappingEngineRunner mapper)
        at AutoMapper.MappingEngine.AutoMapper.IMappingEngineRunner.Map(ResolutionContext context)

Answer 1

使用接口作为目标时,AutoMapper将为您创建代理类型,但这仅支持属性.

要解决这个问题,您可以告诉AutoMapper如何使用构图上的ConstructUsing构建目标对象,因此在上面的示例中,您的创建地图将如下所示......

cfg.CreateMap<MyViewModel, IEntity>().ConstructUsing((ResolutionContext rc) => new MyEntity());

作为参考我从这篇SO文章中找到了这个:https://stackoverflow.com/a/17244307/718672