将应用从netcore 2更新到3不能使用自动映射器

Question

我将应用程序更新为网络核心3，并且在运行应用程序时出现错误关于Automapper（至少我是说）

我更新了运行dotnet -outdate的相对库，然后更新了依赖项

Unhandled exception. System.AggregateException: Some services are not able to be constructed (Error while validating the service descriptor 'ServiceType: MyDemo.Models.Mapping.Resolvers.DefaultResolver Lifetime: Transient ImplementationType: MyDemo.Models.Mapping.Resolvers.DefaultResolver': Unable to resolve service for type 'System.String' while attempting to activate 'MyDemo.Models.Mapping.Resolvers.DefaultResolver'.) (Error while validating the service descriptor 'ServiceType: MyDemo.Models.Mapping.Resolvers.MoneyResolver Lifetime: Transient ImplementationType: MyDemo.Models.Mapping.Resolvers.MoneyResolver': Unable to resolve service for type 'System.String' while attempting to activate 'MyDemo.Models.Mapping.Resolvers.MoneyResolver'.) (Error while validating the service descriptor 'ServiceType: MyDemo.Models.Mapping.Resolvers.TimeSpanResolver Lifetime: Transient ImplementationType: MyDemo.Models.Mapping.Resolvers.TimeSpanResolver': Unable to resolve service for type 'System.String' while attempting to activate 'MyDemo.Models.Mapping.Resolvers.TimeSpanResolver'.)
 ---> System.InvalidOperationException: Error while validating the service descriptor 'ServiceType: MyDemo.Models.Mapping.Resolvers.DefaultResolver Lifetime: Transient ImplementationType: MyDemo.Models.Mapping.Resolvers.DefaultResolver': Unable to resolve service for type 'System.String' while attempting to activate 'MyDemo.Models.Mapping.Resolvers.DefaultResolver'.
 ---> System.InvalidOperationException: Unable to resolve service for type 'System.String' while attempting to activate 'MyDemo.Models.Mapping.Resolvers.DefaultResolver'.
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateArgumentCallSites(Type serviceType, Type implementationType, CallSiteChain callSiteChain, ParameterInfo[] parameters, Boolean throwIfCallSiteNotFound)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.CreateConstructorCallSite(ResultCache lifetime, Type serviceType, Type implementationType, CallSiteChain callSiteChain)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.TryCreateExact(ServiceDescriptor descriptor, Type serviceType, CallSiteChain callSiteChain, Int32 slot)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteFactory.GetCallSite(ServiceDescriptor serviceDescriptor, CallSiteChain callSiteChain)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.ValidateService(ServiceDescriptor descriptor)

    services.AddAutoMapper(typeof(Startup));

似乎是依赖项注入错误，但无法理解

Answer 1

对于您的DefaultResolver，它具有需要传递string memberName的构造函数。

通常，AutoMapper有三种使用自定义值解析器的方式

MapFrom
• MapFrom（typeof（CustomValueResolver））
• MapFrom（aValueResolverInstance）

对于Custom constructor methods，您需要尝试第三个选项，例如：

var configuration = new MapperConfiguration(cfg => cfg.CreateMap<Source, Destination>()
    .ForMember(dest => dest.Total,
        opt => opt.MapFrom(new CustomResolver())
    ));