Two model classes in the same hierarchy with identical field names causes exception

[roji]

Using EF Core 1.1.0, there seems to be an error with two classes included in a model with an inheritance relationship, and which both contain fields with the same name:

public class Parent
{
	public int Id { get; set; }
	public int Foo;
}

public class Child : Parent
{
	public int Id { get; set; }
	public int Foo;
}

public class MyContext : DbContext
{
	protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
		=> optionsBuilder.UseNpgsql("...");

	public DbSet<Parent> Parents { get; set; }
	public DbSet<Child> Children { get; set; }
}

Trying to use this model in any way triggers the following exception:

Unhandled Exception: System.ArgumentException: An item with the same key has already been added.
   at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at System.Linq.Enumerable.ToDictionary[TSource,TKey,TElement](IEnumerable`1 source, Func`2 keySelector, Func`2 elementSelector, IEqualityComparer`1 comparer)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.BackingFieldConvention.TryMatchFieldName(Type entityType, Type propertyType, String propertyName)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.BackingFieldConvention.Apply(PropertyBase propertyBase)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.BackingFieldConvention.Apply(InternalPropertyBuilder propertyBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnPropertyAdded(InternalPropertyBuilder propertyBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.EntityType.AddProperty(String name, Type propertyType, MemberInfo memberInfo, ConfigurationSource configurationSource, Boolean runConventions)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.EntityType.AddProperty(MemberInfo memberInfo, ConfigurationSource configurationSource, Boolean runConventions)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.InternalEntityTypeBuilder.Property(Property existingProperty, String propertyName, Type propertyType, MemberInfo clrProperty, Nullable`1 configurationSource)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.InternalEntityTypeBuilder.Property(String propertyName, Type propertyType, MemberInfo clrProperty, Nullable`1 configurationSource)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.InternalEntityTypeBuilder.Property(MemberInfo clrProperty, ConfigurationSource configurationSource)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.PropertyDiscoveryConvention.Apply(InternalEntityTypeBuilder entityTypeBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnEntityTypeAdded(InternalEntityTypeBuilder entityTypeBuilder)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.Model.AddEntityType(EntityType entityType, Boolean runConventions)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.Model.AddEntityType(Type type, ConfigurationSource configurationSource, Boolean runConventions)
   at Microsoft.EntityFrameworkCore.Metadata.Internal.InternalModelBuilder.Entity(Type type, ConfigurationSource configurationSource, Boolean runConventions)
   at Microsoft.EntityFrameworkCore.ModelBuilder.Entity(Type type)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.FindSets(ModelBuilder modelBuilder, DbContext context)
   at Microsoft.EntityFrameworkCore.Infrastructure.Internal.RelationalModelSource.FindSets(ModelBuilder modelBuilder, DbContext context)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.<>c__DisplayClass14_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.LazyRef`1.get_Value()
   at Microsoft.EntityFrameworkCore.Internal.DbContextServices.get_Model()
   at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServiceCollectionExtensions.<>c.<AddEntityFramework>b__0_6(IServiceProvider p)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactoryService(FactoryService factoryService, 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__DisplayClass16_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.Storage.DatabaseProviderServices.GetService[TService]()
   at Microsoft.EntityFrameworkCore.Storage.Internal.NpgsqlDatabaseProviderServices.get_Creator()
   at Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkServiceCollectionExtensions.<>c.<AddEntityFramework>b__0_13(IServiceProvider p)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitFactoryService(FactoryService factoryService, 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__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
   at Microsoft.EntityFrameworkCore.Infrastructure.AccessorExtensions.GetService[TService](IInfrastructure`1 accessor)
   at Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade.get_DatabaseCreator()
   at Microsoft.EntityFrameworkCore.Infrastructure.DatabaseFacade.EnsureDeleted()
   at Test.Program.Main(String[] args) in c:\projects\Test\Program.cs:line 19

The exception gets thrown from this line:

var fields = entityType.GetRuntimeFields().ToDictionary(f => f.Name);

and the reason is that GetRuntimeFields() returns all the fields from the entire hierarchy, and the ToDictionary() bombs since we have the same name twice.

FYI, this scenario was triggered by including a Code Contract invariant method on both parent and child - CC's rewriter apparently rewrites the classes to add a field with the same name.

[roji]

/cc @damageboy

[damageboy]

Right, as this issue originally happened to me, code contract's adds a compiler/rewriter generated member:
$evaluatingInvariant$ of type bool...