Allow users to send messages to multiple users simultaneously in a messaging app

Question

How is a single message sent to several friends simultaneously in messaging applications? I read in a Django question that this design is a M2M relation. You define 2 models (User and SentMessage) and the backend creates a third object?

For example, Wechat and Facebook Messenger allow you to select multiple friends and send a single message to them simultaneously. How is this done in iOS, Parse or your own Node.js backend?

You define your classes.

user["username"] = String
user["sex"] = String
user["age"] = Int

///

let messageObj = PFObject(className: "Messages")   
messageObj["sender"] = PFUser.current()?.username
messageObj["message"] = messageTextView.text
messageObj["likes"] = [String]()

How would you allow for the sending of messages to:
A. All users simultaneously.
B. Users with specific attributes e.g. ["age"] or ["sex"] simultaneously.

Feel free to contribute solutions for other servers.

score 1 · Accepted Answer · answered Jul 29 '18 at 13:50

In Firebase you model many-to-many relationships with a third "table" too, where you connect items from entity1 one to items of entity2. For more on this see Many to Many relationship in Firebase

But in the case of a chat app, I'd typically model this use-case differently. Sending a message to a group of users typically starts an ad-hoc chat room in those apps. If one of the users answers, that answer goes to everyone else in the group. So you've essentially started a temporary chat room, one that is identified by the people in it.

I typically recommend naming this ad-hoc chat room in Firebase after its participants. For more on this, see: http://stackoverflow.com/questions/33540479/best-way-to-manage-chat-channels-in-firebase. In that model, if you and I start a chat our room would be: uidOfMat_uidOfPuf. So our JSON would look like:

chats: {
  "uidOfMat_uidOfPuf": {
    -Labcdefgh1: {
      sender: "uidOfMat",
      text: "How is a single message sent to several friends simultaneously in messaging applications?"
    }
    -Labcdefgh2: {
      sender: "uidOfPuf",
      text: "In Firebase you model many-to-many relationships with a third "table" too..."
    }

Since the chat room is defined by its participants, any time you and I chat, we end up in this same chat room. Quite handy!

Now say that I ask someone for help answering your question by pulling them into the chat. Since the chat room is defined by its participants, adding a new participant creates a new chat room: uidOfMat_uidOfPuf_uidOfThird. So we end up with:

chats
  uidOfMat_uidOfPuf
    -Labcdefgh1: {
      sender: "uidOfMat",
      text: "How is a single message sent to several friends simultaneously in messaging applications?"
    }
    -Labcdefgh2: {
      sender: "uidOfPuf",
      text: "In Firebase you model many-to-many relationships with a third "table" too..."
    }
  }
  "uidOfMat_uidOfPuf_uidOfThird": {
    -Labcdefgh3: {
      sender: "uidOfPuf",
      text: "Hey Third. Puf here. Mat is wondering how to send a single message to several friends simultaneously in messaging applications. Do you have an idea?"
    }
    -Labcdefgh4: {
      sender: "uidOfThird",
      text: "Yo puf. Long time no see. Let me think for a moment..."
    }

A few things to notice here:

In the model we've used so far, if we'd add yet another person to the uidOfMat_uidOfPuf_uidOfThird chat room, that would again create a new chat room.
Many chat apps give you the option to name a group chat room. In many cases adding a user to such a named chat room does give them access to the message history. I tend to refer to such rooms as persistent chat rooms, since they give access to the historical chat messages.
In our above sample, say that we'd named our 1:1 room "model_chat_room". That would mean that adding the third person to the room, would have given them access to our message history straight away.
On the one hand that is handy, because I wouldn't have had to repeat your question. On the other hand, Matt could have also seen our entire conversation history. Many people consider 1:1 chat conversations private, which is why the "persistent chat room" model is usually only followed for named chats with 3 or more participants.

Thanks. I checked WeChat. You're right. In WeChat you have a button that triggers a "new chat". Then in that window you can select all or some users. When you click done it starts a group chat. How would it be different if it was a company's own server and not Firebase or Parse? How would it be handled in iOS? Goal is to "broadcast" a message to all users in the network who have whatever ["attribute"] such as age 30 then they can reply. Imagine a broadcast of an SOS that sends a push notification but users can reply inside the actionable notification. — MattWright, Jul 30 '18 at 00:19

Allow users to send messages to multiple users simultaneously in a messaging app

1 Answers1

Linked