Exception in TPT models with default values

[dagid4]

I use following version of EF Core:

Microsoft.EntityFrameworkCore.Sqlite 5.0.0-rc.2.20475.6

I have following classes:

public class Garage
{
    public int Id { get; set; }

    public List<Car> Cars { get; set; } = new List<Car>();
}

public class Car
{
    public int Id { get; set; }
}

public class Ferrari : Car
{
    public Special Special { get; set; }
}

public class Special
{
    public int Id { get; set; }
}

public class MyContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        optionsBuilder.UseSqlite($"Filename=my.db");
    }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Garage>().ToTable("Garage");

        modelBuilder.Entity<Car>().ToTable("Car");

        modelBuilder.Entity<Ferrari>().ToTable("Ferrari");

        modelBuilder.Entity<Special>().ToTable("Special");
    }
}

I have following code:

await using var context = new MyContext();

await context.Database.EnsureCreatedAsync();

var garage = new Garage();

context.Add(garage);

await context.SaveChangesAsync();

var ferrari = new Ferrari();

garage.Cars.Add(ferrari);

ferrari.Special = new Special();

Console.WriteLine($"Special reference is null: {(ferrari.Special == null ? "YES" : "NO")}");

await context.SaveChangesAsync();

Console.WriteLine($"Special reference is null: {(ferrari.Special == null ? "YES" : "NO")}");

Reference to Special is getting nulled. The output is following:

Special is null: NO
Special is null: YES

You can try yourself: https://github.com/dagid4/EfCoreBug

In database everything is ok. Do you have please any idea how to solve this problem? Or is it just a bug?

It can be related to derived classes. If you move the Special property from Ferrari into Car, it is working.

[ajcvickers]

I can reproduce this on the 5.0 daily build; it does not repro when switched to TPH. Could be an update pipeline or change tracking bug.
/cc @AndriySvyryd

[AndriySvyryd]

@ajcvickers When propagating the store-generated value to the FK we set the FK store-generated value to null, due to #22603. When accepting the values we overwrite the propagated value with the "store-generated" null

[ajcvickers]

@AndriySvyryd So, does TPT make this common enough that we should patch for #22603?

[AndriySvyryd]

@ajcvickers Yes. In TPH there are no store-generated values in the Ferrari entry at that point so we don't have to reset them to null, however in TPT the Car part is inserted first and that triggers the creation of the store-generated Sidecar, leading to the situation above.

I haven't tried it, but inserting a dependent with 2 principals would likely hit this without TPT.

[dagid4]

Thank you guys, this was driving me crazy. I've tried to build branch Issue23180 and it is now working! Hope it will get into daily builds soon.

[kimimaru4000]

This looks like the issue I'm having on #23158, in which a dependent with two principals is being set to null, thus removing those now-null entries when saving changes again like @AndriySvyryd mentioned. Looking forward to the fix!

[tivtag]

@AndriySvyryd Will your fix be available in some nightly Alpha/Beta channel?
I believe that I am also hitting this problem.

[AndriySvyryd]

@tivtag We don't publish nightly packages for patch releases to avoid overloading the NuGet source. You can try building the package yourself from the release/5.0 branch after #23186 is pushed or wait until December when we'll release 5.0.1