Abstract base class unexpectedly included in TPC model resulting in InvalidOperationException (requires a key to be defined)

[MatthewMWR]

To me seems unexpected, but I could have the wrong expectation.

Exception:

System.InvalidOperationException was unhandled
  HResult=-2146233079
  Message=The entity type 'ConsoleApplication2.ToolBase' requires a key to be defined.
  Source=EntityFramework.Core
  StackTrace:
       at Microsoft.Data.Entity.Internal.ModelValidator.ShowError(String message)
       at Microsoft.Data.Entity.Internal.ModelValidator.EnsureNonNullPrimaryKeys(IModel model)
       at Microsoft.Data.Entity.Internal.ModelValidator.Validate(IModel model)
       at Microsoft.Data.Entity.Internal.RelationalModelValidator.Validate(IModel model)
       at Microsoft.Data.Entity.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator)
       at Microsoft.Data.Entity.Infrastructure.ModelSource.<>c__DisplayClass8_0.<GetModel>b__0(Type k)
       at Microsoft.Data.Entity.Internal.ThreadSafeDictionaryCache`2.GetOrAdd(TKey key, Func`2 factory)
       at Microsoft.Data.Entity.Infrastructure.ModelSource.GetModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator)
       at Microsoft.Data.Entity.Internal.DbContextServices.CreateModel()
       at Microsoft.Data.Entity.Internal.LazyRef`1.get_Value()
       at Microsoft.Data.Entity.Internal.DbContextServices.get_Model()
       at Microsoft.Framework.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c.<AddEntityFramework>b__0_5(IServiceProvider p)
       at Microsoft.Framework.DependencyInjection.ServiceLookup.FactoryService.Invoke(ServiceProvider provider)
       at Microsoft.Framework.DependencyInjection.ServiceProvider.ScopedCallSite.Invoke(ServiceProvider provider)
       at Microsoft.Framework.DependencyInjection.ServiceLookup.ConstructorCallSite.Invoke(ServiceProvider provider)
       at Microsoft.Framework.DependencyInjection.ServiceProvider.ScopedCallSite.Invoke(ServiceProvider provider)
       at Microsoft.Framework.DependencyInjection.ServiceProvider.<>c__DisplayClass12_0.<RealizeService>b__0(ServiceProvider provider)
       at Microsoft.Framework.DependencyInjection.ServiceProvider.GetService(Type serviceType)
       at Microsoft.Framework.DependencyInjection.ServiceProviderExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
       at Microsoft.Framework.DependencyInjection.ServiceProviderExtensions.GetRequiredService[T](IServiceProvider provider)
       at Microsoft.Data.Entity.Storage.DatabaseProviderServices.GetService[TService]()
       at Microsoft.Data.Entity.Storage.Internal.SqlServerDatabaseProviderServices.get_Creator()
       at Microsoft.Framework.DependencyInjection.EntityFrameworkServiceCollectionExtensions.<>c.<AddEntityFramework>b__0_11(IServiceProvider p)
       at Microsoft.Framework.DependencyInjection.ServiceLookup.FactoryService.Invoke(ServiceProvider provider)
       at Microsoft.Framework.DependencyInjection.ServiceProvider.ScopedCallSite.Invoke(ServiceProvider provider)
       at Microsoft.Framework.DependencyInjection.ServiceProvider.<>c__DisplayClass12_0.<RealizeService>b__0(ServiceProvider provider)
       at Microsoft.Framework.DependencyInjection.ServiceProvider.GetService(Type serviceType)
       at Microsoft.Framework.DependencyInjection.ServiceProviderExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
       at Microsoft.Framework.DependencyInjection.ServiceProviderExtensions.GetRequiredService[T](IServiceProvider provider)
       at Microsoft.Data.Entity.Infrastructure.AccessorExtensions.GetService[TService](IAccessor`1 accessor)
       at Microsoft.Data.Entity.Infrastructure.DatabaseFacade.EnsureCreated()
       at ConsoleApplication2.Program.Main(String[] args) in C:\Users\matt\Documents\Visual Studio 2015\Projects\ConsoleApplication2\ConsoleApplication2\Program.cs:line 23
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

Repro:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Threading;
using Microsoft.Data.Entity;

namespace ConsoleApplication2
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            //  build hub/spoke object graph
            var toolboxInstance = new Toolbox() {Title = "This toolbox is red"};
            var hammerInstance = new Hammer() {Description = "My favorite hammer"};
            var wrenchInstance = new Wrench() {Description = "My least favorite wrench"};
            toolboxInstance.Tools.Add(hammerInstance);
            toolboxInstance.Tools.Add(wrenchInstance);

            using (var dbc = new ToolsContext())
            {
                dbc.Database.EnsureCreated();
                dbc.Database.EnsureDeleted();
                dbc.Database.EnsureCreated();

                dbc.Add(toolboxInstance);
                dbc.Add(hammerInstance);
                dbc.Add(wrenchInstance);
                Console.WriteLine(dbc.SaveChanges());
            }

            using (var dbc = new ToolsContext())
            {
                var toolboxesBackFromDb = dbc.Toolboxes.Include(x => x.Tools);
                Console.WriteLine(toolboxesBackFromDb.Count());
                var toolbox1 = toolboxesBackFromDb.AsEnumerable().FirstOrDefault();
                Console.WriteLine(toolbox1.Tools.Any());
            }
            Thread.Sleep(10000);
        }
    }

    public class ToolsContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer(@"server=(localdb)\MsSqlLocalDB;database=HubSpokeExperiment");
        }
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            //  using reflection here to pick up new tool types as they are created
            //  rather than maintaining static list
            foreach (var t in Assembly.GetExecutingAssembly().DefinedTypes.Where(t => t.IsSubclassOf(typeof(ToolBase))))
            {
                var eb = modelBuilder.Entity(t.AsType());
                eb.HasKey("Id");
            }
        }
        public DbSet<Toolbox> Toolboxes { get; set; } 
        public DbSet<ToolBase> Tools { get; set; }
    }

    public class Toolbox
    {
        public Toolbox()
        {
            Tools = new List<ToolBase>();
        }
        public int Id { get; set; }
        public string Title { get; set; }
        public ICollection<ToolBase> Tools { get; set; }
    }

    public abstract class ToolBase
    {
        public string Description { get; set; }
        //public int ToolboxId { get; set; }
    }

    public class Hammer : ToolBase
    {
        public int Id { get; set; }
        public string SomethingAboutHammers { get; set; }
        public Toolbox Toolbox { get; set; }
    }

    public class Wrench : ToolBase
    {
        public int Id { get; set; }
        public string SomethingAboutWrenches { get; set; }
        public Toolbox Toolbox { get; set; }
    }
}

[natemcmaster]

@MatthewMWR Does this error occur if you don't use reflection to loop over all derived types of ToolBase?

[MatthewMWR]

The ToolBase entity gets added to the model whenever DbSet Tools { get; set; } is added to the dbcontext. If I leave OnModelCreating() blank the same thing happens.

[rowanmiller]

Same with this one, if you can retry on the nightly

[smitpatel]

Since the entity Toolbox has collection navigation Tools with target type of ToolBase, it will be added to model. It is essentially following TPH scenario hence throwing exception that base class has no PK defined (in TPH, base class defines PK and all derived classes share it).
As of now TPC support is not fully available. Issue #3170 is tracking it.
@rowanmiller can tell more if this would be possible at present or not.

[divega]

Yes, to have things work exactly like this you will need TPC support which is not planned for EF 7 RTM.

Besides going with TPH another way you can compromise is to not include ToolBase in the model in which case EF will not even reason about the fact that both Wrench and Hammer belong to the same inheritance hierarchy but if you do that then:

1. You cannot have a single DbSet<ToolBase> in the context
2. You cannot have one navigation property of type ICollection<ToolBase> to hold wrenches and hammers.

[divega]

@rowanmiller I think this is just a dupe of #3170.

[smitpatel]

Combining all of the bugs together here #3526 & #3527
@MatthewMWR - The EF nightly has TPH fully implemented and TPC is not fully supported yet hence above model which contains inheritance will be using TPH strategy and won't be valid model since derived types cannot have keys in TPH.

[rowanmiller]

Closing out as this is the correct behavior given that inheritance will always mean TPH at the moment (and TPH will always be the default if nothing is specified in configuration). #3170 is tracking TPC support.