Unclear why zombieToOwner mapping is needed about cryptozombie-lessons HOT 1 CLOSED

Hey. If you question is about why cryptozombies.io use a mapping instead of adding owner as an attribute of the Zombie structure, I could explain it in a way i can.

Let's say we have already added owner as an attribute. This is what might happen:

In order to query who a zombie's owner is. We just need to use:
zombies[_tokenId].owner.
It seems simpler. But truth is that every time we use:
Zombie storage myZombie = zombies[_tokenId] This will cost more space because of one more attribute.
In Ethereum networks, space+time = money. So you don't wanna spend extra fees.

The owner attribute is better be separated because the relations between the two things.
I.E. the relation between the attributes like name, dna ,etc.. and zombie is 1 (per attribute) :1 (per zombie) . But for owner : zombie = 1 : many .

So It makes perfect sense to make a zombieToOwner mapping.
Hope it helps.
If there is any error in the above explanation, please point it out. Thanks!!
Wanna contact me? [email protected]

from cryptozombie-lessons.