Table splitting isn't working with nonnullable reference types.

[bperc2]

With Nullable Reference Types turned on, Entity Framework Core is unable to map two nonnullable reference types to the same column of a table.

Steps to reproduce

To reproduce this issue, I modified the table splitting example of the EF Core documentation: https://docs.microsoft.com/en-us/ef/core/modeling/table-splitting

    public class Order
    {
        public int Id { get; set; }
        public string Category { get; set; }
        public OrderStatus? Status { get; set; }
        public DetailedOrder DetailedOrder { get; set; }
    }

    public class DetailedOrder
    {
        public int Id { get; set; }
        public string Category { get; set; }
        public OrderStatus? Status { get; set; }
        public string BillingAddress { get; set; }
        public string ShippingAddress { get; set; }
        public byte[] Version { get; set; }
    }

    modelBuilder.Entity<DetailedOrder>(dob =>
    {
        dob.ToTable("Orders");
        dob.Property(o => o.Category).HasColumnName("Category");
        dob.Property(o => o.Status).HasColumnName("Status");
    });

    modelBuilder.Entity<Order>(ob =>
    {
        ob.ToTable("Orders");
        ob.Property(o => o.Category).HasColumnName("Category");
        ob.Property(o => o.Status).HasColumnName("Status");
        ob.HasOne(o => o.DetailedOrder).WithOne()
            .HasForeignKey<DetailedOrder>(o => o.Id);
    });

With this setup, adding a migration will fail with the following error message:

'DetailedOrder.Category' and 'Order.Category' are both mapped to column 'Category' in 'Orders' but are configured with different nullability.

Further technical details

EF Core version: 3.0
Database provider: Microsoft.EntityFrameworkCore.SqlServer
Target framework: .NET Core 3.0
Operating system: Windows 10
IDE: Visual Studio 2019 16.3

[AndriySvyryd]

@bperc2 This is not supported yet.

Duplicate of #12100

[flcdrg]

This is a regression from 2.2 where this did work.

[sbojarczak]

I have the same issue again. I've checked #12100, but making Navigation required didn't help. Is it supported or still not? I'm confused

[ajcvickers]

@sbojarczak Please open a new issue and attach a small, runnable project or post a small, runnable code listing that reproduces what you are seeing so that we can investigate.