Mathias Verraes has a new post today with a response to an email he received about some comments on a recent Elephant in the Room podcast about Value Object usage. The question asks about usage of Value Objects, specifically when it comes to things like country information.
There’s nothing intrinsically wrong with modeling countries as entities and storing them in the database. But in most cases, that overcomplicating things. Countries don’t change often. When a country’s name changes, it is in fact, for all practical purposes, a new country. If a country one day does not exist anymore, you can’t simply change all addresses, because possibly the country was split into two countries. Whenever you have this kind of friction, there’s usually some missing concept screaming to be discovered.
He talks some about the concepts around the "country" data and some of the functional concerns around it (duplicate checking, validation of existence, etc). He takes the concept and breaks it out into two different concepts - the actual Value Object of a single country and an "AvailableCountries" set (and "AvailableCountryRepository").