Stroring field name instead of referencing using objectId

This is my first question here

For example: I have a post document which contains list of people who like it and my question is Should i store each person in the array using objectId or username(it’s also a unique identifier) the reason i ask is that when we view a likes of a particular post i want to show only their username and profile pic in this case I think storing username will be much faster than query each objectId and fetch their username, but after all i still need to fetch their profile pic using either one of them.

Guide me if i’m wrong or misunderstood sth.

you can send me if you have any blogs related to this.