Nullable reference with DeleteBehavior.Cascade that is deleted is reloaded back after DetectChanges

[xsmerek]

We are using EF with .NET 6.0 and we have an entity which is child of several other entities:

    public partial class Car
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    public partial class Person
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public Car Car { get; set; } // FK is defined in Car table
    }

All FKs are nullable and defined on Car table and with DeleteBehaviour.Cascade:

                entity.Property<int?>("PersonId").HasMaxLength(100).IsRequired(false);
                entity.HasOne<Person>()
                    .WithOne(p => p.Car)
                    .HasForeignKey<Car>("PersonId")
                    .OnDelete(DeleteBehavior.Cascade);

We want to be able to delete the child by setting parent reference to null:

                person.Car = null;

After ChangeTracker.DetectChanges() is called, the child is correctly marked as deleted but the reference itself is reloaded, so person.Car != null. Having a deleted entity hanging in the reference causes trouble for subsequent business logic.

I tried to debug the issue, it seems to be a combination of InternalEntityEntry.SetProperty() not setting the value of underlying property to null because of DeleteBehaviour.Cascade and the fact that subsequent ChangeDetector.DetectKeyChange() compares snapshot value (contains null) with actual value of underlying property (contains original key).

Steps to reproduce

Project:
https://github.com/xsmerek/EFCoreDeletingNullableReference

Steps:

• run EFCoreDeletingNullableReference\setup.sql to create DB and data.
• adjust connection sting in EFCoreDeletingNullableReferenceContext
• Run test DeleteReferenceTest

Provider and version information

EF Core version: 6.0.0
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET 6.0
Operating system: Windows 10
IDE: Visual Studio 2022 17.0

Please let me know if you need any additional information.

[ajcvickers]

Verified that this is fixed in the latest daily build. Will add a test.