Add-Migration NullReferenceException using App.config. Failing to find config

[TimMcGilly]

I have 3 projects: a DataAccess(.net standard) with dbcontext, a UI project (wpf .net core startup project) and model project (.net standard).
I have a file called App.config in both UI and DataAccess projects with this code

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <connectionStrings>
    <add name="ScreenTimeTrackerDb"
         connectionString="Server=.\SQLExpress;Database=ScreenTimeTracker;Trusted_Connection=True;" />
  </connectionStrings>
</configuration>

I am loading the configuration with System.Configuration and this override

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(ConfigurationManager.ConnectionStrings["ScreenTimeTrackerDb"].ConnectionString);
        }

When running Add-Migration it throws a null-reference exception due to not finding configuration.

System.NullReferenceException: Object reference not set to an instance of an object.
   at ScreenTimeTracker.DataAccess.ScreenTimeTrackerDbContex.OnConfiguring(DbContextOptionsBuilder optionsBuilder) in C:\Users\timmc\source\repos\ScreenTimeTracker\ScreenTimeTracker.DataAccess\ScreenTimeTrackerDbContex.cs:line 13
   at Microsoft.EntityFrameworkCore.DbContext.get_InternalServiceProvider()
   at Microsoft.EntityFrameworkCore.DbContext.Microsoft.EntityFrameworkCore.Infrastructure.IInfrastructure<System.IServiceProvider>.get_Instance()
   at Microsoft.EntityFrameworkCore.Infrastructure.Internal.InfrastructureExtensions.GetService[TService](IInfrastructure`1 accessor)
   at Microsoft.EntityFrameworkCore.Infrastructure.AccessorExtensions.GetService[TService](IInfrastructure`1 accessor)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(Func`1 factory)
   at Microsoft.EntityFrameworkCore.Design.Internal.DbContextOperations.CreateContext(String contextType)
   at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_0.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)

This is run from within visual studio from the Package Managed Console with Default project set to DataAccess and the startup project set to UI.

Using

var configfile = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
            var path = configfile.FilePath;
            throw new System.Exception(path);

it appears it is attempting to open

System.Exception: C:\Users\timmc\source\repos\ScreenTimeTracker\ScreenTimeTracker.UI\bin\Debug\netcoreapp3.1\ef.dll.config` 
whereas the configuration files produced my project are
`ScreenTimeTracker.DataAccess.dll.config`
`ScreenTimeTracker.UI.dll.config`.

Changing the App.config Copy to Output to Copy Always does not resolve the issue.

Further technical details

EF Core version: 3.1.7
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET Core 3.1, .Net Standard 2.1
Operating system:
IDE: Visual Studio 2019 16.7.2

[ajcvickers]

@bricelam to find dupe.

[bricelam]

Blocked on dotnet/runtime#931

[walter-tudorin-ross-rlb]

Experiencing the same issue as described by TimMcGilly. Any progress on this?
Using

• EF 5.0.4
• Winforms App with NET 5
• Separate Assembly for DbContext

[skrabbe001]

What is the status on this, i.e. is there a deadline for when this will be fixed? And for which versions of dotnet will it be fixed? I have had the same problem for approximately a year, but didn't report it.

[ajcvickers]

@skrabbe001 This is currently planned for EF Core 7.0, as indicated by the milestone. This will be released with .NET 7. See the planning process for more information on how we plan what gets fixed in a release.