I\'m having a time trying to wrap my head around what I thought was a simple concept.
I have an app where I sign up a user, allow that user to set a \'photoURL\' to
What you're describing is a typical issue when working with noSQL databases. On the one hand, data duplication makes your app and its queries run faster. On the other hand, if you want to change any that duplicated data, it can be problematic to find and replace all occurrences.
There's no "best" way to determine what to do. It's completely up to your particular case. It sounds like, if you have extreme amounts of data duplication that could be costly to update, it would be better to simply query the user record every time rather than to do the updates. But again, it's ultimately up to you.