public abstract record Customer
    {
        public int Id { get; init; }
        abstract public CustomerType CustomerTypeId { get; }
        public string CustomerNumber { get; init; }
    }

    public record PrivateCustomer : Customer
    {
        public override CustomerType CustomerTypeId => CustomerType.Private;
        public string SocialSecurityNumber { get; init; }
        public string FirstName { get; init; }
        public string LastName { get; init; }
        public string ChangedBy { get; init; }
    }