error in saving two users chat in flutter

Question

I was making chat app in flutter with firebase. I was able to save the users chat in firebase by this function:

await FirebaseFirestore.instance
                        .collection("Chats")
                        .doc(uid! + FirebaseAuth.instance.currentUser!.uid)
                        .collection("messages")
                        .add({
                      FirebaseAuth.instance.currentUser!.uid:
                          chatController.text,
                      
                    }).then((value) => () {
                              b = uid;
                            });

but when I save the one users chat. I was thinking that when I will get the chat of second user. It will return a chat from the doc I was saving the both users chat. But unfortunately when I save the users chat it saves a new doc named first users id and then second users id, in first users chat it saves doc named the second user id and first users id. I know what is the reason from which it was happening but how can I resolve that, I mean how can I save the both users chat in one doc

Update: the function I have tried based on Frank's answer:

 var docId = uid
        .toString()
        
        .compareTo(FirebaseAuth.instance.currentUser!.uid) > 0;

the function used for printing docId:

    IconButton(
              icon: Icon(Icons.send),
              iconSize: 20.0,
              onPressed: () async { print(docId);}
            )

score 1 · Accepted Answer · answered May 01 '22 at 14:44

1

You need to have a deterministic ID for the document.

One simple way to do this is to always alphabetically order the two UIDs with something like this:

const docId = uid!.compareTo(FirebaseAuth.instance.currentUser!.uid) > 0 
  ? uid! + FirebaseAuth.instance.currentUser!.uid 
  : FirebaseAuth.instance.currentUser!.uid + uid! 

await FirebaseFirestore.instance
                        .collection("Chats")
                        .doc(docId)
                        ...

For more on this, see the examples in my answer here: Best way to manage Chat channels in Firebase

answered May 01 '22 at 14:44

Frank van Puffelen

565,676
79
828
807

thanks Frank I was thinking that it will work but when I print the value of docId it was giving me zero so how can I resolve that – Ammar Mohib May 03 '22 at 11:40
"but when I print the value of docId it was giving me zero" That seems unexpected. Can you edit your question, and add an update to show how you implemented this, including the print statement and its output? – Frank van Puffelen May 03 '22 at 14:14
sorry for delay but I have updated and added the function I tried – Ammar Mohib May 03 '22 at 16:26
The first statement in my answer consists of three lines, but you only copied the first one. That now means that your `docId` is a boolean value, instead of the concatenated string as it is in my code. – Frank van Puffelen May 03 '22 at 17:09
Ok I will also try that – Ammar Mohib May 03 '22 at 17:29
It is resolved and thanks – Ammar Mohib May 03 '22 at 19:41

error in saving two users chat in flutter

1 Answers1