ISO-codes VS date-time

ronanguilloux/isocodes: PHP library - Validators for standards from ISO, International Finance, Public Administrations, GS1, Manufacturing Industry, Phone numbers & Zipcodes for many countries

brick/date-time: Date and time library for PHP

brick/date-time: Date and time library for PHP

If you're happy to bring in another library, you could replace your Date VO class with the LocalDate class from the brick/datetime library. It does the same thing, just has three int fields inside instead of a string in Y-m-d format.

If you need to store subsets of a date-time-timezone combination, then take a look at brick/date-time instead.

Slightly related but https://github.com/brick/date-time is a wonderful library to manage datetime concepts in a proper way.

Looks like a CivilDate is the same thing that brick/date-time calls a LocalDateTime. Does this library have any advantages over the one from Brick?

I like https://github.com/brick/date-time

It is a good practice to use an interface to manage the clock in an application, as it allows having full control of time. For example, it eases testing, as it lets us define the concrete time for each test. Frank de Jonge and Matthias Noback have blog posts about it, brick has an implementation, and there is even a PSR proposal to have a ClockInterface.