Best Practice to keep user data in firebase firestore?

Question

I am using firebase as a backend for my Android App. And this app is a social media app where users can post, comment & like. so I am storing user data in user_collection and this collection is secured by security rules where if uid == auth.uid (any user can only access data of himself).

Now in this app when a user post something every user can see this post. And in post_collection I am saving userId in post_doc.

So the problem is I need to show name of user to other users and I have only userId but the problem is a user can't get name of other user by uid beacuse of security rules. now I have to solutions for this please tell me which one is better or you can also suggest any other solutions also?

1. I can use cloud functions getUserNameById() (Problem : I need to call this function very frequently in feed when user scroll)

2. I can store name also in post_doc (problem : when user changes his name then It will show old name in old post)

Thanks for you kind help

Answer 1

Consider the solution: whatever public data you need (author name, author userpic link etc) just save it with the post at the time it had created. So your Message Pojo will looks like:

• id
• authorName
• text

etc..

and just display this name (authorName). It will be the bad way to go any time to User_collection folder to take the name even if there are would be not strict security (becouse it takes time and document reads)

Answer 2

In a scenario like the one you describe, I would typically store the user name in each post doc. I would also ignore updates to the name, as I think of the user name in the post doc as a historical value: this is the name the user had when they posted this. Now you may want different behavior of course, in which case I recommend reading: How to write denormalized data in Firebase

---

Your approach with Cloud Functions is fine too, and quite common in some situations. But I tend to only use Cloud Functions for reading data, it the read operation itself is particularly complex, which isn't the case here. In a case like this, I'd recommend coming up with a data model that allows the use-case and security you want.

For example: if you create a collection usernames where each document has the UID as its document ID, and then contains a single field with the username for that UID, you could implement the lookup of the user name through Firestore.

So you could have:

1. Store the full user profile in /users/$uid.
2. Store the user name in /usernames/$uid.
3. Have a Cloud Function that triggers when /users/$uid is written and that updates /usernames/$uid.
4. The client then has read access to each /usernames/$uid document, or even to the entire /usernames collection in one go if needed.

This way the names can be cached on the client, and continue to work when the app is offline, unlike in your approach with a Cloud Function that looks up the user name.