Show private messages list of multiple users logged in at the same time

Question

I've created a private messaging app where users login and can view their private messages. The problem that I am having is that is only shows the message list of one logged in user at a time. So let's say User A is logged in, it will show the chat list of user A. But then User B logs in, then both User A and User B will see the chat list of User B.

This is my server side call to fetch chats by user id: Im using express for the backend

io.on('connection', socket => {
  socket.on('findAllChatsByUserId', (userId) => {
    socket.userId = userId
    socket.join(socket.userId)
    ChatModel.aggregate([{$match: {$or:[{senderId: userId},{receiver: userId}]}}, {$group: {_id:     '$chatId', 'data': {$last: '$$ROOT'}}}]).exec(function(error, data) {
      if (error) {
        return error
      } else {
        data.sort(function (a, b) {
          return b.data.date - a.data.date;
        });
        io.to(socket.userId).emit('findAllChatsByUserId', data);
      }
    })
  })
});

And on the client side I do: I am using VueJs on the FE

  mounted () {
    this.loading = true
    this.socket.emit('findAllChatsByUserId', this.getUserId) // this calls the socket to get the chats for the given user Id
    this.loading = false
  },

I tried creating rooms by userId to make sure that only the data for a given user ID is passed in but it seems like only one user can use the socket at a time. I thought the rooms would solve this issue for me. Do I have to create a separate socket for each user? If so, how do I do that? I've followed the socket.io private messaging tutorial but they use 2 users talking to each other to explain the problem.

Answer 1

So I ended up solving this by doing:

io.to(socket.id).emit('findAllChatsByUserId', data);

instead of:

io.to(socket.userId).emit('findAllChatsByUserId', data);

So you use the "to" attribute to make sure the data you're sending is going to a particular socket, and you can find your specific socket by just calling socket.id (you don't have to set this, it gets set on its own. And the data will get emitted to whomever is on that specific socket.