Grouping participants of users on nodejs with mongodb

Question

I'm new in MongoDB Here is the thing I want to implement using mongoose and nodejs How to do a grouping of participants basics on room description.

//here is the schema

rooms.js

  //ROOMS
const schema = mongoose.Schema({
    "total_participants":{type: Number, default: 3},
    "group_id": {type:String, default: ()=>utils.randomString(16)}
}

participants.js

    //participants
        const schema = mongoose.Schema({
            ---,
            "group_id":String
        });

API code, when someone joins the room, When someone tries to join first it gets groupId from the room and saves in participants and then it checks total no of joined participants in that room and if I got full than it generates a new id and updates in the room

        const room= await RoomModel.findOne({_id: "5f2fde82b64b4e1c787ea611"})
        await new ParticipantsModel({"group_id": room.group_id}).save()

        const newGroupId= utils.randomString(16)
        const filled =await ParticipantsModel.countDocuments({group_id: room.group_id})
        console.log("filled "+filled)
        await RoomModel.updateOne({total_participants:filled},{group_id: newGroupId}).exec()

The problem I'm facing here is when multiple user send at same time like 50 user send join request togher than the total participants in the room gets more in the room and new room Id not get updated .

Answer 1

It could be a concurrency issue; by the time you are inserting a new participant, the room is not marked as full yet and another one can get in.

In this case you need to use a transaction: https://mongoosejs.com/docs/transactions.html