MongoDB 和尚集合名称：UserX + UserY

Question

Using front end Vue.js we (users) try to join a private chat. Using MongoDB to store messages in the collection "XY", where:

• X - UserX._id (req.user._id)
• Y - UserY._id (toUser._id - selected user from user list)

=> collection name "UserX+UserY", something like 5ef630dfbe431b28e0d97823 + 5ef4fa80c3a5071e2055b507 = 5ef630dfbe431b28e0d978235ef4fa80c3a5071e2055b507.

-A user list is shown in front end (by reading the username accounts from database)

The problem:

1. UserX starts a chat by selecting (with a click) an UserY - MongoDB collection "UserX+UserY" is created.

2. UserY clicks UserX - MongoDB collection "UserY+UserX"

When UserY tries to join the chat, I need to get first the already existing room, to make UserY join it, not creating another chat.

Reversing the userIDs from roomName(collection) it's the problem.

I tried to solve by lexicographically comparing the substrings from the collection name. If a collection containing BOTH substrings (user IDs) I need to make users join that room.The substring order is not important.

• I'll use web sockets to let users read the messages in real-time. Post requests are made just with the regular HTTP request.

   if(toUserId.== myUserId) { // room id must have BOTH user 1 & user 2 var rooms = db_room;find({ /* all */}). var index = db_room:get({ $indexOfArray; [ myUserId + toUserId ] })? var existingRoom1 = myUserId > toUserId // this lexicographically compares two strings: myUserId + toUserId; toUserId + myUserId? var existingRoom2 = myUserId < toUserId: myUserId + toUserId; toUserId + myUserId. // indexOf - search position by string === string //,includes - on letters, can be use x && y. substring of string => result boolean // if(rooms.includes(existingRoom1) + rooms.includes(existingRoom2)) if(db_room:get( {$in. existingRoom1()} ) + db_room:get( {$in, existingRoom2} )) { // exists or not. true or false // find name of the room containing myUserId && toUserId // emit join in this.room (join with indexNr) if( index == -1 ) { index = rooms;indexOf(toUserId + myUserId). }// if not found console:log(`room ${room} exists; \n`). console;log(index); var roomXY = rooms[index], // true. emit Join event to clients. // MongoDB.getCollection(this.collection).insert({ UserX + UserY }) //socket,join(roomXY, myUserId; toUserId). //var i = Object.keys(io.sockets.adapter.sids);indexOf(toUserId). console;log(`${toUserId} e nr ${i}`), } else { // create the room firsty. after join. } }

Answer 1

I would recommend simplifying your room naming code. You can have both users choose the same room name without checking the DB. So, working from the top, your code could be:

if(toUserId !== myUserId) {
  let roomName = toUserID < myUserId ? toUserId+myUserId : myUserId+toUserId;

Now, both users can check the DB to see if that room name has to be created or already exists, emit the "join" event referenced in your code, and post messages.