Model configuration: Incorrect key discovery can result in exception saying another instance has same key, but it doesn't

[HappyNomad]

The issue can be reproduced with this version:

"Microsoft.EntityFrameworkCore.SqlServer": "1.2.0-preview*",

and this context:

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

	public DbSet<L> Ls { get; set; }
	public DbSet<AL> ALs { get; set; }
}

and this model:

public class L
{
	public int ID { get; set; }
	public IList<T> Ts { get; set; }
}

public class T : P
{
	public Q D { get; set; }
	public P P { get; set; }
	public Q F { get; set; }
}

public class P : PBase { }

public class Q : PBase { }

public abstract class PBase
{
	public int ID { get; set; }
	public string Stuff { get; set; }
}

public class AL
{
	public int ID { get; set; }
	public PBase L { get; set; }
}

The "seeding" code is:

dataContext.Ls.Add(
	new L {
		Ts = new[] { new T { D = new Q(), F = new Q() } }
	}
);

The exception is:

System.InvalidOperationException was unhandled by user code
  HResult=-2146233079
  Message=The instance of entity type 'Q' cannot be tracked because another instance of this type with the same key is already being tracked. When adding new entities, for most key types a unique temporary key value will be created if no key is set (i.e. if the key property is assigned the default value for its type). If you are explicitly setting key values for new entities, ensure they do not collide with existing entities or temporary values generated for other new entities. When attaching existing entities, ensure that only one entity instance with a given key value is attached to the context.
  Source=Microsoft.EntityFrameworkCore
  StackTrace:
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(TKey key, InternalEntityEntry entry)
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.IdentityMap`1.Add(InternalEntityEntry entry)
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.StateManager.StartTracking(InternalEntityEntry entry)
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState oldState, EntityState newState, Boolean acceptChanges)
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetEntityState(EntityState entityState, Boolean acceptChanges)
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.PaintAction(EntityEntryGraphNode node)
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph(EntityEntryGraphNode node, Func`2 handleNode)
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph(EntityEntryGraphNode node, Func`2 handleNode)
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityEntryGraphIterator.TraverseGraph(EntityEntryGraphNode node, Func`2 handleNode)
       at Microsoft.EntityFrameworkCore.ChangeTracking.Internal.EntityGraphAttacher.AttachGraph(InternalEntityEntry rootEntry, EntityState entityState)
       at Microsoft.EntityFrameworkCore.DbContext.SetEntityState(InternalEntityEntry entry, EntityState entityState)
       at Microsoft.EntityFrameworkCore.DbContext.SetEntityState[TEntity](TEntity entity, EntityState entityState)
       at Microsoft.EntityFrameworkCore.DbContext.Add[TEntity](TEntity entity)
       at Microsoft.EntityFrameworkCore.Internal.InternalDbSet`1.Add(TEntity entity)
       at EFGetStarted.AspNetCore.NewDb.Startup.Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory, BloggingContext dataContext) in C:\Users\Adrian\Development\Examples\ASP.NET Core\EFGetStarted.AspNetCore.NewDb\src\EFGetStarted.AspNetCore.NewDb\Startup.cs:line 61
  InnerException: 

[ajcvickers]

Note for triage: Looks like ID in PBase, inherited by Q, is not getting ValueGenerated.OnAdd.

Here is the model:

Model: 
  EntityType: AL
    Properties: 
      ID (int) Required PK ReadOnlyAfterSave RequiresValueGenerator ValueGenerated.OnAdd 0 0 0 -1 0
      LID (no field, Nullable<int>) Shadow FK Index 1 1 1 0 -1
    Navigations: 
      L (<L>k__BackingField, PBase) ToPrincipal PBase 0 -1 2 -1 -1
    Keys: 
      ID PK
    Foreign keys: 
      LID -> PBase.ID ToPrincipal: L
    Annotations: 
      Relational:TableName: ALs
      RelationshipDiscoveryConvention:NavigationCandidates: System.Collections.Immutable.ImmutableSortedDictionary`2[System.Reflection.PropertyInfo,System.Type]
  EntityType: L
    Properties: 
      ID (int) Required PK ReadOnlyAfterSave RequiresValueGenerator ValueGenerated.OnAdd 0 0 0 -1 0
    Navigations: 
      Ts (<Ts>k__BackingField, IList<T>) Collection ToDependent T 0 -1 1 -1 -1
    Keys: 
      ID PK
    Annotations: 
      Relational:TableName: Ls
      RelationshipDiscoveryConvention:NavigationCandidates: System.Collections.Immutable.ImmutableSortedDictionary`2[System.Reflection.PropertyInfo,System.Type]
  EntityType: P Base: PBase
    Annotations: 
      Relational:DiscriminatorValue: P
      RelationshipDiscoveryConvention:NavigationCandidates: System.Collections.Immutable.ImmutableSortedDictionary`2[System.Reflection.PropertyInfo,System.Type]
  EntityType: PBase Abstract
    Properties: 
      ID (int) Required PK ReadOnlyAfterSave 0 0 0 -1 -1
      Discriminator (no field, string) Shadow Required ReadOnlyAfterSave RequiresValueGenerator 1 1 -1 0 -1
        Annotations: 
          ValueGeneratorFactory: System.Func`3[Microsoft.EntityFrameworkCore.Metadata.IProperty,Microsoft.EntityFrameworkCore.Metadata.IEntityType,Microsoft.EntityFrameworkCore.ValueGeneration.ValueGenerator]
      Stuff (string) 2 2 -1 -1 -1
    Keys: 
      ID PK
    Annotations: 
      Relational:DiscriminatorProperty: Discriminator
      Relational:DiscriminatorValue: PBase
      RelationshipDiscoveryConvention:NavigationCandidates: System.Collections.Immutable.ImmutableSortedDictionary`2[System.Reflection.PropertyInfo,System.Type]
  EntityType: Q Base: PBase
    Annotations: 
      Relational:DiscriminatorValue: Q
      RelationshipDiscoveryConvention:NavigationCandidates: System.Collections.Immutable.ImmutableSortedDictionary`2[System.Reflection.PropertyInfo,System.Type]
  EntityType: T Base: P
    Properties: 
      DID (no field, Nullable<int>) Shadow FK Index 3 3 1 1 -1
      FID (no field, Nullable<int>) Shadow FK Index 4 4 2 2 -1
      LID (no field, Nullable<int>) Shadow FK Index 5 5 3 3 0
      PID (no field, Nullable<int>) Shadow FK Index 6 6 4 4 -1
    Navigations: 
      D (<D>k__BackingField, Q) ToPrincipal Q 0 -1 5 -1 -1
      F (<F>k__BackingField, Q) ToPrincipal Q 1 -1 6 -1 -1
      P (<P>k__BackingField, P) ToPrincipal P 2 -1 7 -1 -1
    Foreign keys: 
      DID -> PBase.ID ToPrincipal: D
      FID -> PBase.ID ToPrincipal: F
      LID -> L.ID ToDependent: Ts
      PID -> PBase.ID ToPrincipal: P
    Annotations: 
      Relational:DiscriminatorValue: T
      RelationshipDiscoveryConvention:NavigationCandidates: System.Collections.Immutable.ImmutableSortedDictionary`2[System.Reflection.PropertyInfo,System.Type]
Annotations: 
  ProductVersion: 1.2.0-csproj
  SqlServer:ValueGenerationStrategy: IdentityColumn

[HappyNomad]

My workaround has been to rename my model's "ID" properties to "Id", so I thought the fix would be simply to add IgnoreCase or the like somewhere. Has this turned out to be more complicated?

[AndriySvyryd]

@HappyNomad The issue is that we aren't always running the conventions. The fix I sent has problems though, so I'll send out a different one.