Why you should use Value Objects in your Code

Bending the Clean Architecture Principles

Introduction

Every now and then, I try to revisit some of my old projects, or even explore on GitHub what’s trendy. In this journey, I found a common problem that I was addressed a lot:

• Primitive Type obsession
• Strongly Typed IDs

What

All of us developers worked with some generic entities like a User, an Order, Money, or anything really… It even goes beyond that, I saw my sister’s introductory programming course at school. One of the questions were:

How do you represent someone’s Age?

Naively, the right answer was an Integer. Which is not wrong in a sense, but it got me thinking, if I would ask this question to the community, what will they answer?

I think most of them will use an Integer without ever looking back. So let’s do that for a second.

Trading Shoes

I hope you got that Eminem reference, our Age is just a number right? So I used an integer for my User class. That’s great but now, how do I initialize it?

I added a default value, because we can’t have an age of 0. Now, our new intern decided to change the age of our users. He wanted to calculate it from the date of birth and the current date. But little did he know that his calculations were wrong due to the inconsistency of DateTime.Now, so a person would have a different age depending on the region.

Now, here’s the fun part. This calculation algorithm loophole ended up setting a negative Age for example. What did your application do about it? You let it live and work with it. So as the Mind Flayer of the project, you decide we should add some sort of business validation on the Age. But where do you add it?

Do you have to implement it every time you are setting an Age, or add it on the setter of the property?

Things started to go sideways so you decide to take an ever more extreme approach and removing an external setter, the Age should not change in a given context for the User right? so why do we have a setter. You are setting this value only from the constructor now, while adding the business logic to validate it there.