DDD - Share or duplicate a value object to be used between two aggregate roots?

Question

If I have a payment value object can it be shared by two different aggregate roots? or should I duplicate it?

Both options feel wrong!

Portal

Is the answer in this post suggesting it is ok to share #7478179? – Portal

Why do they feel wrong? A value object represents a value of a business concepts as defined by the language of the bounded context. – Clearing

Actually it's only the duplication that feels wrong. Sharing it feels right... but what is Eric referring to when he says: "Nothing outside the Aggregate boundary can hold a reference to anything inside except to the root Entity"? – Portal

It means that anyone using the aggregate must do it via the aggregate root. In short, only the aggregate root is 'usable' directly. – Clearing

That's what I thought. So a Value object in AR1 should not be accessible by AR2. The problem is the value object in AR1 makes perfect sense in AR2 as well... now I am starting to think the two aggregate roots belong in different BCs. – Portal

No, a value object is just a value, the 'reference' is for entities. It doesn't matter that the implementation of a value object is a class, the DDD reference has nothing to do with an object reference from OOP. DDD doesn't care what programming language you're using. – Clearing

right... so you're saying the same value object can be used inside different aggregates? – Portal

@user2909756 Yes, VO types can can be shared by any number of Aggregates in the same BC. – Joaquin

The whole point of VOs being immutable is that they can be shared between various ARs/entities/clients without being afraid of side effects. – Murmurous

Answer 1

As long as your VO is immutable, you can share it without any issues. However, Evans prohibits sharing mutable VOs and I think you will also agree with that.

Callery

That makes perfect sense. Thank you for the clarification :) – Portal