Which is better data schema for chat app in Firebase

Question

This is a group chat app using Firebase. I have few data schema option and I don't know what would be better for performance and less data usage.

Let's suppose there are 10 rooms. this rooms is already made.

Each room's id is [A, B, C, D, E, F, G, H, I, J]

Option 1

/users
- /$uid/joined
  - room1 { roomId : A }
/rooms
- room1 { roomId: A, users : [ ... ] }
/messages
- room1 { roomId: A, messages : [ ... ] }

Option 2

/users
- /$uid/joined
  - room1 { roomId : A, lastChecked, joinedAt... }
/rooms
- room1 { roomId : A, users : [], messages : [] }

Which is better? First time I planned to use Option 1. For decreasing data usage, I want to handle room's brief information and messages separately. But during of developing, I realized the firebase's database is handled by specific keys...

For example, when user access to a room,

Update his/her joined room information at /users/$uid/joined, uid needed.
Update room's joined users at /rooms/$roomKey/users, roomKey needed, and I have to query it using room's Id(A)
After access room, Get messages at /rooms/$key/messages and its key is different with above $roomKey.

Above is option 1's scenario, and If I use option 2, I don't need to get messages again in different path. But the reason of why I ask of this question, Then how about rendering "The list of joined rooms" screen? each room should has a brief information such as title, the number of users, the count of unread messages. If I put messages to /rooms, the messages will queried together. right?

I think the messages is the biggest data size. How can I make this data structure?

Reflekti0n Reflekti0n · Accepted Answer · 2017-08-27T08:40:18

I would take the the 2. option because it's easier to manage the security rules, but the 1. option is not wrong or bad ^^

If you want to keep the size of the data small and don't want to waste anything, you can choose this structure:

- users
  - $uid ....

- rooms
  - $roomid
    - info
      - title
      - description
      - ....
    - messages
      - $messageid
      - ....
    - users

Now you load only the child the is required at the moment. But your security rules are still compact.

Which is better data schema for chat app in Firebase

2 Answers