Add-Migration error: The key {'TempId'} contains properties in shadow state and is referenced by a relationship

[saf-itpro]

In my following Model if I have the following the Add-Migration command works fine but if I replace datatype of StateName from string to List<SelectListItem> I get the error shown below. I'm using latest ASP.NET Core 1.0 and VS2015-Update 3 on win 8.1. I've just added the following class in the Model of this MSDN tutorial:

public class State
    {
        public int StateId { get; set; }
        public string StateCode { get; set; }
        public string StateName { set; get; } //Add-Migration works but does NOT work if datatype string is replaced with `List<SelectListItem>` 
    }

Error:

[System.InvalidOperationException: The key {'TempId'} contains properties in shadow state and is referenced by a relationship from 'SelectListGroup' to 'SelectListItem.Group'. Configure a non-shadow principal key for this relationship. at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.KeyConvention.Apply(InternalModelBuilder modelBuilder) at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnModelBuilt(InternalModelBuilder modelBuilder) at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator) at System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory) at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel() at Microsoft.EntityFrameworkCore.Internal.LazyRef1.get_Value()
at Microsoft.Extensions.DependencyInjection.ServiceProvider.ScopedCallSite.Invoke(ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.TransientCallSite.Invoke(ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceLookup.ConstructorCallSite.Invoke(ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceProvider.TransientCallSite.Invoke(ServiceProvider provider)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
at Microsoft.EntityFrameworkCore.Design.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
at Microsoft.EntityFrameworkCore.Tools.Cli.MigrationsAddCommand.Execute(CommonOptions commonOptions, String name, String outputDir, String context, String environment, Action1 reporter) at Microsoft.EntityFrameworkCore.Tools.Cli.MigrationsAddCommand.<>c__DisplayClass0_0.<Configure>b__0() at Microsoft.Extensions.CommandLineUtils.CommandLineApplication.Execute(String[] args) at Microsoft.EntityFrameworkCore.Tools.Cli.Program.Main(String[] args) The key {'TempId'} contains properties in shadow state and is referenced by a relationship from 'SelectListGroup' to 'SelectListItem.Group'. Configure a non-shadow principal key for this relationship. ](url)

[Bartmax]

You are trying to add SelectListItem to your model, that's not how it's supposed to work.

The error is because it can't create a shadow property with a key to the parent. (SelectListItem has string and your State Id is int)

Maybe you can make it somehow work by adding a key explicit using Fluent API. Still, adding a SelectList entity (class owned by MVC) into your database model is not a good idea.

disclaimer: I'm not very familiar with EF, so take everything said with a grain of salt.

[smitpatel]

When you include navigation of type List<SelectListItem> that will bring SelectListItem as entity type in model. And all other types referenced by properties in it will be also brought in the model (recursively). See https://ef.readthedocs.io/en/latest/modeling/included-types.html#id2 to know how conventions discover types through navigations.
Every entity type must have a non-shadow primary key defined on them and every relationship must be pointing to a non-shadow key. Since those classes discovered by conventions may not have a property named Id, shadow keys are created temporarily which are not replaced with non-shadow keys hence eventually it throws exception like above.
As @Bartmax said, it is really bad idea to bring in types which are not domain classes because you cannot be sure of their shapes as a proper entity type and related entity types they may discover further.

[rowanmiller]

Given that SelectListItem doesn't have a property that can be used as a primary key, the best option would be to create an entity class that wraps SelectListItem and captures that data that needs to be saved/queried. In the future, something like our Flexible Mapping feature (#240) would make reading/writing from/to a SelectListItem property a possibility.