如何删除值对象中的值对象 [DDD]

Question

I have a question regarding DDD. How do I remove a VO in a VO ? So I have aggregate x with a VO y. In VO y there is a list of VO z. zListVO

Now I want to remove a zVO from the aggregate.

Can i do : (method in application layer)

public void main 
{
  y.remove(zVO z)
}

AGGREGATE X

private void Handle(RemovedZDE z)
{
    this.x.remove(z.z);
}

And then make a method in VO Y where I remove z from their list of VO ?

Class yVO

protected void Remove(zVO z)
{
  zListVO.remove(z);
}

Answer 1

Typically, instances of the value object pattern are immutable; you don't typically have commands (in the CQS sense), just queries.

Therefore, it is more common to see something like

new_y = old_y.remove(z)

I have aggregate x with a VO y. In VO y there is a list of VO z. zListVO

The basic idea is going to look like:

X::remove(Z z) {
   old_y = this.y
   new_y = old_y.remove(z)

   // X is an entity, so we normally update its state directly
   this.y = new_y
}

Y::remove(Z z) {
    old_list = y.zListVO
    new_list = old_list.remove(z)
    // Y is a value, so we create a new value to describe
    // the change
    return new Y(new_list)
}