entity framework - System.NotSupportedException: Unable to determine the provider name for provider factory of type 'System.Data.SqlClient.SqlClientFactory'

Question

I am using EF6 with Asp.net core and I am getting error when I call to db through dbcontext :

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:Usersiradm1DocumentsVisual Studio 2017ProjectsCoreWithEFCoreWithEFcontrollersSampleController.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

The error Unable to determine the provider name... can indicate the .csproj for the Core project is not set correctly per the instructions on Get Started with ASP.NET Core and Entity Framework 6.

In my case I was working with Core 2.2 project and trying to leverage Entity Framework 6 from .Net Framework 4.7.1 class library, but failed to change the Core .csproj file from <TargetFramework>netcoreapp2.2</TargetFramework> to <TargetFramework>net471</TargetFramework>.

When I finally made the target framework change, the next error to appear was Microsoft.AspNetCore.All 2.2.1 is not compatible with net471 (.NETFramework,Version=v4.7.1). I removed the NuGet Microsoft.AspNetCore.All package, which then created a lot of missing reference build errors.

To resolve the build errors I had to google the missing type to find the assembly name, add that specific NuGet package, rebuild, then keep repeating the process until all of my build errors were resolved.

Every project is different, but here were the packages I had to add to fix my build issues after removing 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" />

After build issues were resolved and the project built successfully, my DotNet Core 2.2 API was able to return data using Entity Framework 6 from the class library project.

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To summarize, the System.NotSupportedException occurred because the generated Entity Framework classes (in the .NET Framework 471 class library) were being accessed by the DotNet Core version of Entity Framework and not the .NET Framework 4.7.1 version of Entity Framework.

Before making the changes listed above, evaluating System.Data.Common.DbProviderFactories.GetFactoryClasses().Rows in the Immediate debug window showed an empty collection of providers. After making the changes, the Factory Classes included the Odbc, OleDb, Oracle, SqlServer providers.

More specifically if you evaluate the rows individually, you should see the providers are from the Full .NET Framework.

For example: System.Data.Common.DbProviderFactories.GetFactoryClasses().Rows[3].ItemArray (for me) showed it came from "System.Data.SqlClient.SqlClientFactory, System.Data, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089”.