自动映射器自定义解析器抛出空异常

Question

所以我有一个移动服务运行良好，并希望添加DTOs的符号。 我使用AutoMapper在我的模型和DTO模型之间进行映射，但是数据库的复杂性和结果我迫使我使用自定义解析器，而这又会引发空异常。

具体 - 映射器初始化

Mapper.Initialize(cfg => 
     { 
      cfg.CreateMap<Contact, MobileContact>() 
       .ForMember(mobcont => mobcont.Favorite, map => map.ResolveUsing<ContactResolver>());//.UseValue(true));// 
      cfg.CreateMap<MobileContact, Contact>(); 
     }); 

而且我自定义的解析器是

public class ContactResolver : ValueResolver<Contact, bool> 
{ 
    protected override bool ResolveCore(Contact a) 
    { 
     return true; 
    } 
} 

编辑：最喜欢的当然是

的布尔如果我不使用自定义解析器和使用.UseValue（true）它工作得很好

尽管如上图所示用自定义解析器一个共同的GET请求抛出以下异常：

Exception=System.NullReferenceException: Object reference not set to an instance of an object. 
    at AutoMapper.QueryableExtensions.Extensions.ResolveExpression(PropertyMap propertyMap, Type currentType, Expression instanceParameter) 
    at AutoMapper.QueryableExtensions.Extensions.CreateMemberBindings(IMappingEngine mappingEngine, TypePair typePair, TypeMap typeMap, Expression instanceParameter, IDictionary`2 typePairCount) 
    at AutoMapper.QueryableExtensions.Extensions.CreateMapExpression(IMappingEngine mappingEngine, TypePair typePair, Expression instanceParameter, IDictionary`2 typePairCount) 
    at AutoMapper.QueryableExtensions.Extensions.CreateMapExpression(IMappingEngine mappingEngine, TypePair typePair, IDictionary`2 typePairCount) 
    at AutoMapper.QueryableExtensions.Extensions.<>c__DisplayClass1`2.<CreateMapExpression>b__0(TypePair tp) 
    at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory) 
    at AutoMapper.Internal.DictionaryFactoryOverride.ConcurrentDictionaryImpl`2.GetOrAdd(TKey key, Func`2 valueFactory) 
    at AutoMapper.QueryableExtensions.Extensions.CreateMapExpression[TSource,TDestination](IMappingEngine mappingEngine) 
    at AutoMapper.QueryableExtensions.ProjectionExpression`1.To[TResult]() 
    at Microsoft.WindowsAzure.Mobile.Service.MappedEntityDomainManager`2.Query() 
    at azmobtestService.Models.MobileContactDomainManager.Query() in c:\Users\n.atlas\Source\Repos\JPhoneBook\Service\azmobtestService\Models\MobileContactDomainManager.cs:line 104 
    at Microsoft.WindowsAzure.Mobile.Service.TableController`1.Query(), Id=75849f58-ccb0-4a6b-8a77-491f13fcb717, Category='App.Controllers.Tables' 

Answer 1

如果你正在做的是在任何情况下解决的喜爱，真正的（这是不正确的，但是这是代码你提供的，所以我用它去），那么你的映射器可能只是.ForMember(mobcont => mobcont.Favorite, expression => expression.MapFrom(source => true));

如果您正在寻找正常的值解析器，我会用ITypeConverter是这样的：

public class ContactToMobileContactTypeConverter : ITypeConverter<Contact, MobileContact> 
{ 
    public MobileContact Convert(ResolutionContext context) 
    { 
     var contact = (Contact)context.SourceValue; 

     var mobileContact = new MobileContact(); 
     if(contact != null) { 
      //database query 
      //assign values 
     } 
     return mobileContact; 
    } 
}