System.NotSupportedException：无法确定类型为'System.Data.SqlClient.SqlClientFactory'的提供程序工厂的提供程序名称。

Question

我使用带有Asp.net核心的EF6，通过dbcontext调用db时出现错误：

System.NotSupportedException: Unable to determine the provider name for provider factory of type 'System.Data.SqlClient.SqlClientFactory'. Make sure that the ADO.NET provider is installed or registered in the application config.
   at System.Data.Entity.Utilities.DbProviderFactoryExtensions.GetProviderInvariantName(DbProviderFactory factory)
   at System.Data.Entity.Infrastructure.DependencyResolution.DefaultInvariantNameResolver.GetService(Type type, Object key)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   at System.Linq.Enumerable.SelectArrayIterator`2.MoveNext()
   at System.Linq.Enumerable.TryGetFirst[TSource](IEnumerable`1 source, Func`2 predicate, Boolean& found)
   at System.Data.Entity.Infrastructure.DependencyResolution.ResolverChain.GetService(Type type, Object key)
   at System.Linq.Enumerable.SelectArrayIterator`2.MoveNext()
   at System.Linq.Enumerable.TryGetFirst[TSource](IEnumerable`1 source, Func`2 predicate, Boolean& found)
   at System.Data.Entity.Infrastructure.DependencyResolution.ResolverChain.GetService(Type type, Object key)
   at System.Data.Entity.Infrastructure.DependencyResolution.CompositeResolver`2.GetService(Type type, Object key)
   at System.Data.Entity.Infrastructure.DependencyResolution.DbDependencyResolverExtensions.GetService[T](IDbDependencyResolver resolver, Object key)
   at System.Data.Entity.Utilities.DbConnectionExtensions.GetProviderInvariantName(DbConnection connection)
   at System.Data.Entity.Internal.InternalConnection.get_ProviderName()
   at System.Data.Entity.Internal.DefaultModelCacheKeyFactory.Create(DbContext context)
   at System.Data.Entity.Internal.LazyInternalContext.InitializeContext()
   at System.Data.Entity.Internal.InternalContext.Initialize()
   at System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType(Type entityType)
   at System.Data.Entity.Internal.Linq.InternalSet`1.Initialize()
   at System.Data.Entity.Internal.Linq.InternalSet`1.get_InternalContext()
   at System.Data.Entity.Infrastructure.DbQuery`1.System.Linq.IQueryable.get_Provider()
   at System.Linq.Queryable.FirstOrDefault[TSource](IQueryable`1 source)
   at CoreWithEF.controllers.SampleController.GetStudentDetails() in C:\Users\biradm1\Documents\Visual Studio 2017\Projects\CoreWithEF\CoreWithEF\controllers\SampleController.cs:line 27
   at lambda_method(Closure , Object , Object[] )
   at Microsoft.Extensions.Internal.ObjectMethodExecutor.Execute(Object target, Object[] parameters)
   at Microsoft.AspNetCore.Mvc.Internal.ActionMethodExecutor.SyncObjectResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.InvokeActionMethodAsync()}  System.NotSupportedException

Answer 1

错误Unable to determine the provider name...可能表明.csproj，根据ASP.NET Core和Entity Framework 6入门中的说明未正确设置Core项目的。

就我而言，我正在与Core 2.2项目一起工作，并尝试利用.Net Framework 4.7.1类库中的Entity Framework 6，但未能将Core .csproj文件从更改<TargetFramework>netcoreapp2.2</TargetFramework>为<TargetFramework>net471</TargetFramework>。

当我最终更改目标框架时，出现的下一个错误是Microsoft.AspNetCore.All 2.2.1 is not compatible with net471 (.NETFramework,Version=v4.7.1)。我删除了NuGet Microsoft.AspNetCore.All程序包，然后创建了许多缺少的参考构建错误。

要解决构建错误，我必须用谷歌搜索缺少的类型以找到程序集名称，添加特定的NuGet程序包，进行重建，然后继续重复此过程，直到解决了我所有的构建错误。

每个项目都是不同的，但是在删除后，我必须添加以下软件包来解决我的构建问题Microsoft.AspNetCore.All：

<PackageReference Include="EntityFramework" Version="6.2.0" />
<PackageReference Include="Microsoft.AspNetCore" Version="2.2.0" />
<PackageReference Include="Microsoft.AspNetCore.Diagnostics" Version="2.2.0" />
<PackageReference Include="Microsoft.AspNetCore.Http.Abstractions" Version="2.2.0" />
<PackageReference Include="Microsoft.AspNetCore.HttpsPolicy" Version="2.2.0" />
<PackageReference Include="Microsoft.AspNetCore.Mvc" Version="2.2.0" />
<PackageReference Include="Microsoft.AspNetCore.Razor.Design" Version="2.2.0" PrivateAssets="All" />
<PackageReference Include="System.Configuration.ConfigurationManager" Version="4.5.0" />

解决了构建问题并成功构建了项目之后，我的DotNet Core 2.2 API能够使用Entity Framework 6从类库项目中返回数据。

总而言之，System.NotSupportedException发生这种情况是因为所生成的Entity Framework类（在.NET Framework 471类库中）是由Entity Framework的DotNet Core版本而不是Entity Framework的.NET Framework 4.7.1版本访问的。

在进行上面列出的更改之前，System.Data.Common.DbProviderFactories.GetFactoryClasses().Rows在“立即调试”窗口中进行评估显示提供程序为空集合。进行更改后，工厂类包括Odbc，OleDb，Oracle，SqlServer提供程序。

更具体地说，如果您分别评估行，则应该看到提供程序来自完整的.NET Framework。

例如：（System.Data.Common.DbProviderFactories.GetFactoryClasses().Rows[3].ItemArray对我来说）表明它来自"System.Data.SqlClient.SqlClientFactory, System.Data, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089”。