如何在EntityFrameworkCore5/6中映射Nullable<Ulid>（或任何其他可為null的自定義結(jié)構(gòu)）？

采用以下實(shí)體框架核心實(shí)體類：

public interface IEntity
{
    public Ulid Id { get; set; }
}

public class User : IEntity
{
    [Key]
    public Ulid Id { get; set; }
    public string Email { get; set; } = default!;
    public string FirstName { get; set; } = default!;
    public string LastName { get; set; } = default!;
    public Ulid? CompanyId { get; set; }

    // Navigation properties
    public Company? Company { get; set; } = default!;
}

注意，主鍵是non-nullableUlid，它是這個(gè)第三方庫(kù)中定義的結(jié)構(gòu)，允許在數(shù)據(jù)庫(kù)之外生成可排序的唯一標(biāo)識(shí)符。

我將Ulid映射到實(shí)體框架DbContext中的PostgreSQLbytea列，如下所示，按照這里的庫(kù)說(shuō)明：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    var bytesConverter = new UlidToBytesConverter();

    foreach (var entityType in modelBuilder.Model.GetEntityTypes())
    {
        // Don't use database-generated values for primary keys
        if (typeof(IEntity).IsAssignableFrom(entityType.ClrType))
        {
            modelBuilder.Entity(entityType.ClrType)
                .Property<Ulid>(nameof(IEntity.Id)).ValueGeneratedNever();
        }

        // Convert Ulids to bytea when persisting
        foreach (var property in entityType.GetProperties())
        {
            if (property.ClrType == typeof(Ulid) || property.ClrType == typeof(Ulid?))
            {
                property.SetValueConverter(bytesConverter);
            }
        }
    }
}

public class UlidToBytesConverter : ValueConverter<Ulid, byte[]>
{
    private static readonly ConverterMappingHints DefaultHints = new ConverterMappingHints(size: 16);

    public UlidToBytesConverter(ConverterMappingHints? mappingHints = null)
        : base(
                convertToProviderExpression: x => x.ToByteArray(),
                convertFromProviderExpression: x => new Ulid(x),
                mappingHints: DefaultHints.With(mappingHints))
    {
    }
}

這個(gè)映射對(duì)于non-nullableulid很好，但是User.CompanyId屬性不能被映射，因?yàn)樗梢詾閚ull（這反映了User可以選擇屬于Company的事實(shí)）。具體來(lái)說(shuō)，我得到以下錯(cuò)誤：

System.InvalidOperationException: The property 'User.CompanyId' could not be mapped because it is of type 'Nullable<Ulid>', which is not a supported primitive type or a valid entity type. Either explicitly map this property, or ignore it using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.ValidatePropertyMapping(IModel model, IDiagnosticsLogger`1 logger)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelValidator.Validate(IModel model, IDiagnosticsLogger`1 logger)
...

是否可以在efcore5/6中映射自定義的可空結(jié)構(gòu)類型？如果可以，如何映射？我花了幾個(gè)小時(shí)研究實(shí)體框架文檔Google和Github，但沒(méi)有找到一個(gè)明確的答案。