ForeignKeyAttribute prevents inverse navigation to be properly matched up

[Wouter8]

I've created a relatively complex structure of entities. I'm creating a quiz site and on this site I want to have multiple types of questions and therefor also custom types of answers.

I've created a simple method where an answer gets created based on the type of question it is answering. The object I'm getting is correct - it has the correct type and all fields are filled in correctly as well. Upon saving the context with a newly added answer of type MultipleAnswersRepeating I get an error that entity framework is trying to cast my object to another answer type, MultipleAnswers.

Unable to cast object of type xxx.Models.Answers.MultipleAnswersRepeating' to type 'xxx.Models.Answers.MultipleAnswers'

See the class definitions:

    public class MultipleAnswers : Answer
    {
        [ForeignKey("AnswerId")]
        public virtual ICollection<Partials.PartialAnswer> Answers { get; set; }
    }

    public class MultipleAnswersRepeating : Answer
    {
        [ForeignKey("AnswerId")]
        public virtual ICollection<Partials.PartialAnswerRepeating> Answers { get; set; }
    }


    public class PartialAnswerRepeating : PartialAnswer
    {
    }

    public class PartialAnswer : PartialAnswerBase
    {
    }

I'm getting exactly the same error in a very small project with just the relevant classes. You can find this project here.

I have specified all types that inherit from a base class in OnModelCreating.

        public DbSet<Answer> Answers { get; set; }
        public DbSet<PartialAnswerBase> PartialAnswers { get; set; }

        protected override void OnModelCreating(ModelBuilder builder)
        {
            // Answers
            builder.Entity<MultipleAnswers>();
            builder.Entity<MultipleAnswersRepeating>();

            // PartialAnswers
            builder.Entity<PartialAnswer>();
            builder.Entity<PartialAnswerRepeating>();

        }

If you are seeing an exception, include the full exceptions details (message and stack trace).

Exception message:
Unable to cast object of type 'EFErrorTest.Models.Answers.MultipleAnswersRepeating' to type 'EFErrorTest.Models.Answers.MultipleAnswers'.

Stack trace:

Microsoft.EntityFrameworkCore.Metadata.Internal.ClrICollectionAccessor`3.GetCollection(Object instance)\r\n   at
Microsoft.EntityFrameworkCore.Metadata.Internal.ClrICollectionAccessor`3.GetOrCreateCollection(Object instance)\r\n   at Microsoft.EntityFrameworkCore.Metadata.Internal.ClrICollectionAccessor`3.Add(Object instance, Object value)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.AddToCollection(InternalEntityEntry entry, INavigation navigation, InternalEntityEntry value)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.KeyPropertyChanged(InternalEntityEntry entry, IProperty property, IReadOnlyList`1 containingPrincipalKeys, IReadOnlyList`1 containingForeignKeys, Object oldValue, Object newValue)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntryNotifier.KeyPropertyChanged(InternalEntityEntry entry, IProperty property, IReadOnlyList`1 keys, IReadOnlyList`1 foreignKeys, Object oldValue, Object newValue)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.ChangeDetector.DetectKeyChange(InternalEntityEntry entry, IProperty property)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntryNotifier.PropertyChanged(InternalEntityEntry entry, IPropertyBase property, Boolean setModified)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetProperty(IPropertyBase propertyBase, Object value, Boolean setModified)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.SetForeignKeyProperties(InternalEntityEntry dependentEntry, InternalEntityEntry principalEntry, IForeignKey foreignKey, Boolean setModified)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.NavigationFixer.KeyPropertyChanged(InternalEntityEntry entry, IProperty property, IReadOnlyList`1 containingPrincipalKeys, IReadOnlyList`1 containingForeignKeys, Object oldValue, Object newValue)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntryNotifier.KeyPropertyChanged(InternalEntityEntry entry, IProperty property, IReadOnlyList`1 keys, IReadOnlyList`1 foreignKeys, Object oldValue, Object newValue)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.ChangeDetector.DetectKeyChange(InternalEntityEntry entry, IProperty property)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntryNotifier.PropertyChanged(InternalEntityEntry entry, IPropertyBase property, Boolean setModified)\r\n   at 
Microsoft.EntityFrameworkCore.ChangeTracking.Internal.InternalEntityEntry.SetProperty(IPropertyBase propertyBase, Object value, Boolean setModified)\r\n   at 
Microsoft.EntityFrameworkCore.Update.ColumnModification.set_Value(Object value)\r\n   at Microsoft.EntityFrameworkCore.Update.ModificationCommand.PropagateResults(ValueBuffer valueBuffer)\r\n   at 
Microsoft.EntityFrameworkCore.Update.AffectedCountModificationCommandBatch.ConsumeResultSetWithPropagation(Int32 commandIndex, RelationalDataReader reader)\r\n   at 
Microsoft.EntityFrameworkCore.Update.AffectedCountModificationCommandBatch.Consume(RelationalDataReader reader)

[ajcvickers]

Note for triage: this also repros on 3.0 preview 7.

[Wouter8]

@ajcvickers please let me know whenever you have an estimate for when this will be resolved. I need it for my project (which isn't live yet) and might need to disable some functionality until it's fixed.

Thanks in advance.

[ajcvickers]

@AndriySvyryd Can you take a look at this?

@Wouter8 We'll have a better idea once we understand the issue. It may get fixed for the 3.0 release, but since that release is already over-booked we may have to push it out to a later release.

[AndriySvyryd]

@Wouter8 As a workaround remove the ForeignKeyAttributes and configure the relationships explicitly:

builder.Entity<MultipleAnswers>().HasMany(m => m.Answers).WithOne(p => (MultipleAnswers)p.Answer).HasForeignKey(p => p.AnswerId);
builder.Entity<MultipleAnswersRepeating>().HasMany(m => m.Answers).WithOne(p => (MultipleAnswersRepeating)p.Answer).HasForeignKey(p => p.AnswerId);

[Wouter8]

Awesome, I'll try that after my vacation. Thanks for getting back to me.

[Wouter8]

@Wouter8 As a workaround remove the ForeignKeyAttributes and configure the relationships explicitly:

builder.Entity<MultipleAnswers>().HasMany(m => m.Answers).WithOne(p => (MultipleAnswers)p.Answer).HasForeignKey(p => p.AnswerId);
builder.Entity<MultipleAnswersRepeating>().HasMany(m => m.Answers).WithOne(p => (MultipleAnswersRepeating)p.Answer).HasForeignKey(p => p.AnswerId);

Tried this solution. This does generate a new column in the new migration, PartialAnswers.MultipleAnswersId specifically. This shouldn't be necessary since PartialAnswers.AnswerId should be used.

This new column doesn't even work, since it'll leave the existing AnswerId empty. @AndriySvyryd am I missing something? I've updated the sample project with your proposed solution (https://github.com/Wouter8/EFErrorTest)

[ajcvickers]

@AndriySvyryd Simplified repo and model built on current nightly:

[Table("Answers")]
public abstract class Answer
{
    public int Id { get; set; }
}

public class PartialAnswer : PartialAnswerBase
{
}

[Table("PartialAnswers")]
public class PartialAnswerBase
{
    public int Id { get; set; }
    public int AnswerId { get; set; }

    [ForeignKey("AnswerId")]
    public virtual Answer Answer { get; set; }
}

public class PartialAnswerRepeating : PartialAnswer
{
}

public class MultipleAnswers : Answer
{
    public virtual ICollection<PartialAnswer> Answers { get; set; }
}

public class MultipleAnswersRepeating : Answer
{
    public virtual ICollection<PartialAnswerRepeating> Answers { get; set; }
}

public class BloggingContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        => optionsBuilder
            .UseSqlServer(@"Server=(localdb)\mssqllocaldb;Database=Test;ConnectRetryCount=0");

    public DbSet<Answer> Answers { get; set; }
    public DbSet<PartialAnswerBase> PartialAnswers { get; set; }

    protected override void OnModelCreating(ModelBuilder builder)
    {
        // Answers
        builder.Entity<MultipleAnswers>()
            .HasMany(m => m.Answers)
            .WithOne(p => (MultipleAnswers)p.Answer)
            .HasForeignKey(p => p.AnswerId);
        builder.Entity<MultipleAnswersRepeating>()
            .HasMany(m => m.Answers)
            .WithOne(p => (MultipleAnswersRepeating)p.Answer)
            .HasForeignKey(p => p.AnswerId);

        // PartialAnswers
        builder.Entity<PartialAnswer>();
        builder.Entity<PartialAnswerRepeating>();
    }
}

public class Program
{
    public static async Task Main()
    {
        using (var context = new BloggingContext())
        {
            var model = context.Model;
        }
    }
}

Model: 
  EntityType: Answer Abstract
    Properties: 
      Id (int) Required PK AfterSave:Throw ValueGenerated.OnAdd
      Discriminator (no field, string) Shadow Required
    Keys: 
      Id PK
  EntityType: MultipleAnswers Base: Answer
    Navigations: 
      Answers (<Answers>k__BackingField, ICollection<PartialAnswer>) Collection ToDependent PartialAnswer
  EntityType: MultipleAnswersRepeating Base: Answer
    Navigations: 
      Answers (<Answers>k__BackingField, ICollection<PartialAnswerRepeating>) Collection ToDependent PartialAnswerRepeating Inverse: Answer
  EntityType: PartialAnswer Base: PartialAnswerBase
    Properties: 
      MultipleAnswersId (no field, Nullable<int>) Shadow FK Index
    Foreign keys: 
      PartialAnswer {'MultipleAnswersId'} -> MultipleAnswers {'Id'} ToDependent: Answers
  EntityType: PartialAnswerBase
    Properties: 
      Id (int) Required PK AfterSave:Throw ValueGenerated.OnAdd
      AnswerId (int) Required FK Index
      Discriminator (no field, string) Shadow Required
    Keys: 
      Id PK
  EntityType: PartialAnswerRepeating Base: PartialAnswer
    Navigations: 
      Answer (<Answer>k__BackingField, Answer) ToPrincipal MultipleAnswersRepeating Inverse: Answers
    Foreign keys: 
      PartialAnswerRepeating {'AnswerId'} -> MultipleAnswersRepeating {'Id'} ToDependent: Answers ToPrincipal: Answer

[AndriySvyryd]

@Wouter8 For this to work PartialAnswerRepeating needs to derive from PartialAnswerBase