无法加载文件或程序集'System.ComponentModel.Annotations

Question

我有一个调用 .NetStandard2.0 项目的 Framework 4.7.2 单元测试

调试器指示测试在某些数据访问代码中失败。

错误是

Test method UnitTestProject3.UnitTest1.TestMethod1 threw exception: 
System.IO.FileNotFoundException: Could not load file or assembly 'System.ComponentModel.Annotations, Version=4.2.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
    at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.CoreConventionSetBuilder.CreateConventionSet()
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateConventionSet(IConventionSetBuilder conventionSetBuilder)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.<>c__DisplayClass5_0.<GetModel>b__1()
   at System.Lazy`1.CreateValue()
   at System.Lazy`1.LazyInitValue()
   at System.Lazy`1.get_Value()
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.GetModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator)
   at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel()
   at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model()
   at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServicesBuilder.<>c.<TryAddCoreServices>b__7_2(IServiceProvider p)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass1_0.<RealizeService>b__0(ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngine.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.ServiceProviderEngineScope.GetService(Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at Microsoft.EntityFrameworkCore.DbContext.get_DbContextDependencies()
   at Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider()
   at Microsoft.EntityFrameworkCore.DbContext.get_DbContextDependencies()
   at Microsoft.EntityFrameworkCore.DbContext.get_Model()
   at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.get_EntityType()
   at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.get_EntityQueryable()
   at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.System.Linq.IQueryable.get_Provider()
   at System.Linq.Queryable.SingleOrDefault[TSource](IQueryable`1 source, Expression`1 predicate)
   at SBD.VivPackAndSend.PackAndSend.GetReadyBy(Int32 headId, String connectionString) in D:\devnet10\SBD.Common\SBD.VivPackAndSend\PackAndSend.cs:line 65
   at UnitTestProject3.UnitTest1.TestMethod1() in D:\devnet10\SBD.Common\UnitTestProject3\UnitTest1.cs:line 15

.NetStandard2.0项目文件是

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Library</OutputType>
    <TargetFramework>netstandard2.0</TargetFramework>
    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
  <ApplicationIcon />
    <StartupObject />
    <SignAssembly>true</SignAssembly>
    <AssemblyOriginatorKeyFile>Software by Design.snk</AssemblyOriginatorKeyFile>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="2.2.6" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Relational" Version="2.2.6" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="2.2.6" />
    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="2.2.0" />
  </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\StandardCommon\SBD.StandardCommon.csproj" />
  </ItemGroup>

</Project>

我查看了this similar question 并尝试使用 VS2019->Tools->Manage Nuget Packages 添加对 System.ComponentModel.Annotations 的引用以获取解决方案

但可用的最低版本是 4.4.0

我试过了，但没有用。

Answer 1

此错误表示缺少数据库连接。我认为你应该在单元测试中剔除真正的数据库层。

Answer 2

我在 .netcore2.1 测试项目中尝试了单元测试。 我在那里遇到了一个不同的错误，这让我意识到我的连接字符串有问题。

当我修复连接字符串时，.netcore2.1 测试项目通过，而 Framework 4.7.2 项目失败并显示不同的错误消息

因此这个特殊问题似乎是我的连接字符串。