[ForeignKey] ignored with alternate principal key

[bricelam]

This code...

class TestContext : DbContext
{
    protected override void OnConfiguring(DbContextOptionsBuilder options)
        => options.UseSqlServer(@"Data Source=(local)\MSSQLLocalDB;Initial Catalog=TestApp");

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Car>().HasOne(d => d.Color).WithMany()
            .HasPrincipalKey(p => p.ColorCode);
    }
}

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

    public string? ColorCode { get; set; }

    [ForeignKey(nameof(ColorCode))]
    public virtual Color? Color { get; set; }
}

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

    public string ColorCode { get; set; } = null!;
}

...produces this model.

EntityType: Car
  Properties:
    Id (int) Required PK AfterSave:Throw ValueGenerated.OnAdd
    ColorCode (string)
    ColorCode1 (no field, string) Shadow FK Index
  Navigations:
    Color (Color) ToPrincipal Color
  Keys:
    Id PK
  Foreign keys:
    Car {'ColorCode1'} -> Color {'ColorCode'} ToPrincipal: Color ClientSetNull
  Indexes:
    ColorCode1

The ForeignKey attribute is completely ignored. A ColorCode1 shadow property is introduced instead.

[ajcvickers]

Note from triage: Likely fix is to re-trigger the foreign key attribute convention when the principal key changes.

[AndriySvyryd]

Could be related to #30344