public class Order : Entity
{
    public Order(KitchenAppContext context) : base(context)
    {

    }
    public Order() : base()
    {

    }
    public DateTime Date { get; set; }
    public Guid MenuId { get; set; }
    public virtual Menu Menu { get; set; }
    public bool IsClosed { get; set; }
    public decimal Price { get; set; }
    public virtual int PeopleCount { get { return Details.Count; } }
    public virtual List<OrderDetail> Details { get; set; } = new List<OrderDetail>();
}

 public class OrderDetail : Entity
{
    public OrderDetail(KitchenAppContext context) : base(context)
    {

    }

    public OrderDetail() : base()
    {

    }
    public Guid UserId { get; set; }
    public virtual User User { get; set; }
    public virtual List<PaymentDetail> Payments { get; set; } = new List<PaymentDetail>();
    public virtual Order Order { get; set; }
    public Guid OrderId { get; set; }
}

void OrderMapping(ModelBuilder builder)
    {
        var etBuilder = builder.Entity<Order>();
        etBuilder.HasKey(m => new { m.Id });
        etBuilder.HasOne(o => o.Menu).WithMany(a => a.Orders).HasForeignKey(f => f.MenuId);
        etBuilder.HasMany(o => o.Details).WithOne(d => d.Order).HasForeignKey(f => f.OrderId);
    }

  void OrderDetailMapping(ModelBuilder builder)
    {
        var etBuilder = builder.Entity<OrderDetail>();
        etBuilder.HasKey(m => new { m.Id });
        etBuilder.HasOne(o => o.User).WithMany(u => u.Details).HasForeignKey(f => f.UserId);
        etBuilder.HasOne(o => o.Order).WithMany(u => u.Details).HasForeignKey(f => f.OrderId);
        etBuilder.HasMany(o => o.Payments).WithOne(d => d.OrderDetail).HasForeignKey(f => f.OrderDetailId);
    }

var order = new Order(Context);
        Context.Orders.Add(order);
        var oderDetail = new OrderDetail(Context) { Order = order };