Looking for pseudo code of best/clean way to create and check unique room "names" for every chat between two users using socket.io/react.js/mongodb - mongodb

Question

my flow:
User A selects user B in the user list:
system needs to check if a room for these two users exists, if not create unique room name and then join both users to the room
if exists, then just join users to the room they were already in and populate the chat with previous msges
Now what I am stuck at is how to exactly do it. Few options I am playing with in my head:
a) First how do i create the unique name that ties both users? Sure I can use string combination for both users, for example user A clicks user B --> "A&B", but this won't work when user B clicks user A, because that will be "B&A". I am struggling with creating dynamic unique names that could be applied to both.
b) do I keep an array with the two users info in the specific room saved in DB, and then check the array if user exists in it already? if so just use that room id as the room name? What is the best flow to save created rooms? Do i save by room name, which I guess would act as unique Id as well?
c) should I be checking the DB EVERYTIME user clicks another user to start a chat just to check if a room exists or not?
I know how to create rooms and all that jazz but what I am really struggling with is how to dynamically create room names so that its the same whether A clicks B or B clicks A and how to from a pseudo code level, store created rooms in DB and check for many users.

Answer 1

Here's an idea: Store the room in your database as a document that contains fields user1 and user2, which will contain the IDs of these users. Specifically, ensure that user1 < user2. When you need to query for this document later, you can do db.rooms.findOne({user1: smallerId, user2: largerId}). Then you can either store the room name and not use it in your queries, or you can even generate the displayed room name dynamically at runtime.
This has the benefit of not only guaranteeing the structure of a room document, but making your queries more efficient as well (you're comparing binary vs. comparing strings). There's also the benefit of not breaking the query when a user's name changes.
In general it's recommended that a document A that's associated with a different document B should refer to document B by an immutable ID, rather than by a mutable name. In this case since a room is associated with two users, have room refer to each user's ID.