Metadata: Discovering derived type with self ref relationship before base causes exception

[KarlGong]

I am migrating from .net core 1.1 to 2.0 and I meet a error when I add entityframeworkcore migrations.

I have two models.

public class TestNode
{
    public int Id { get; set; }

    public TestNode Parent { get; set; }

    public List<TestNode> Children { get; set; } = new List<TestNode>();
}

public class TestCase : TestNode
{
     public string Description { get; set; }
}

And I configured an ApplicationDbContext.

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
            : base(options)
    {
    }

    public DbSet<TestNode> TestNodes { get; set; }

    public DbSet<TestCase> TestCases { get; set; }
}

Then I executed add-migration init in console. Following error occurred

Microsoft.AspNetCore.DataProtection.KeyManagement.XmlKeyManager[0]
      User profile is available. Using 'C:\Users\karl.gong\AppData\Local\ASP.NET\DataProtection-Keys' as key repository and Windows DPAPI to encrypt keys at rest.
System.InvalidOperationException: Nullable object must have a value.
   at System.ThrowHelper.ThrowInvalidOperationException(ExceptionResource resource)
   at System.Nullable`1.get_Value()
   at Microsoft.EntityFrameworkCore.Metadata.Internal.InternalEntityTypeBuilder.DetachRelationship(ForeignKey foreignKey)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.InternalEntityTypeBuilder.HasBaseType(EntityType baseEntityType, ConfigurationSource configurationSource)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.DerivedTypeDiscoveryConvention.Apply(InternalEntityTypeBuilder entityTypeBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ImmediateConventionScope.OnEntityTypeAdded(InternalEntityTypeBuilder entityTypeBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.RunVisitor.VisitOnEntityTypeAdded(OnEntityTypeAddedNode node)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnEntityTypeAddedNode.Accept(ConventionVisitor visitor)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ConventionVisitor.Visit(ConventionNode node)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ConventionVisitor.VisitConventionScope(ConventionScope node)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ConventionBatch.Run()
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ConventionBatch.Dispose()
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.RelationshipDiscoveryConvention.DiscoverRelationships(InternalEntityTypeBuilder entityTypeBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.RelationshipDiscoveryConvention.Apply(InternalEntityTypeBuilder entityTypeBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.ImmediateConventionScope.OnEntityTypeAdded(InternalEntityTypeBuilder entityTypeBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnEntityTypeAdded(InternalEntityTypeBuilder entityTypeBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.Model.AddEntityType(EntityType entityType)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.Model.AddEntityType(Type type, ConfigurationSource configurationSource)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.InternalModelBuilder.Entity(TypeIdentity type, ConfigurationSource configurationSource)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.InternalModelBuilder.Entity(Type type, ConfigurationSource configurationSource)
   at Microsoft.EntityFrameworkCore.ModelBuilder.Entity(Type type)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelCustomizer.FindSets(ModelBuilder modelBuilder, DbContext context)
   at Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelCustomizer.FindSets(ModelBuilder modelBuilder, DbContext context)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelCustomizer.Customize(ModelBuilder modelBuilder, DbContext context)
   at Microsoft.EntityFrameworkCore.Infrastructure.RelationalModelCustomizer.Customize(ModelBuilder modelBuilder, DbContext context)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.<>c__DisplayClass5_0.<GetModel>b__0(Object k)
   at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
   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_1(IServiceProvider p)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactory(FactoryCallSite factoryCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(IServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass22_0.<RealizeService>b__0(ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.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.Microsoft.EntityFrameworkCore.Infrastructure.IInfrastructure<System.IServiceProvider>.get_Instance()
   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_1.<.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)
Nullable object must have a value.

The trick is that if I change the line public DbSet<TestCase> TestCases { get; set; } in ApplicationDbContext to public DbSet<TestCase> XXXXs { get; set; }, IT WORKS!

Is TestCases a reserved word?

Thanks,
Karl

[smitpatel]

The base class TestNode has one-to-many self-ref relationship.
If TestCase derived type is discovered before TestNode then it throws.

[AndriySvyryd]

Impact: Self-referencing relationships cause exceptions if a derived type is configured
Risk: Low, the fix only affects the negative scenario

[SpiraMira]

Deriving from a self-referencing entity is an important pattern for us. Is there a recommended work around?

[AndriySvyryd]

@SpiraMira The workaround is to force the derived type to be discovered last. This could be accomplished in several ways:

• Renaming TestCases to something like ZTestCases as sets are discovered in alphabetical order.
• Removing the derived set property and configuring the entity type in OnModelCreating.
• Adding a NotMapped annotation on the self-ref navigation and configuring it in OnModelCreating.

[SpiraMira]

@AndriySvyryd Thanks for the quick turn-around. This will help.

Regards.

[Eilon]

This patch bug is approved for the 2.0.x patch. Please send a PR to the feature/2.0.1 branch and get it reviewed and merged. When we have the rel/2.0.1 branches ready please port the commit to that branch.

[Eilon]

Hi, we have a public test feed that you can use to try out the ASP.NET/EF Core 2.0.3 patch!

To try out the pre-release patch, please refer to the following guide:

• ASP.NET/EF Core 2.0.3 patch pre-release test feed aspnet/Announcements#274 (info)
• ASP.NET/EF Core 2.0.3 patch pre-release test feed - discussion aspnetcore#2254 (discussions and questions)

We are looking for feedback on this patch. We'd like to know if you have any issues with this patch by updating your apps and libraries to the latest packages and seeing if it fixes the issues you've had, or if it introduces any new issues. If you have any issues or questions, please reply on this issue to let us know as soon as possible.

Thanks,
Eilon