The Value of Value Objects

For years I’ve struggled with how to handle very simple validation scenarios. Most systems have identifiers with basic constraints — fixed length, allowed characters, or formatting rules. The problem usually isn’t writing the validation itself, but deciding where that validation should live and ensuring it’s applied consistently . Consider a simple example: suppose our application models an Order, and the system requires that an order ID must be exactly 10 characters long. For a long time I would have implemented it like this: public class Order { public string Id { get ; set ; } = string . Empty ; } Nothing unusual there. Also, until fairly recently I would typically enforce validation using a separate validator: public class OrderValidator { public void Validate ( Order order ) { ArgumentNullException . ThrowIfNull ( order ); ArgumentException . ThrowIfNullOrWhiteSpace ( order . Id ); if ( order . Id . Trim (). Length != 10 ) { throw new ArgumentException ( "Id must be 10 characters