How to store users and groups for a chat using Firebase

Question

I would like to make a chat using Firebase. I need to display for each users the list of group they belong to and also for each group all the members.

Because of ho

Answer 1

The data model you have proposed is consistent with recommendations for firebase. A more detailed explanation is outlined in best way to structure data in firebase

users/userid/groups
groups/groupid/users

Firebase provides .transaction for atomic operations. You may chain multiple transactions to ensure data consistency. You may also use onComplete callback function. For detailed explanation refer to firebase transaction. I am using this same approach to keep multiple message counts up to date for a dashboard display.

Sample code for nested transaction:

ref.child('users').child(userid).child(groupid).transaction(function (currentData) {
  if (currentData === null) {
    return groupid;
  } else {
    console.log('groupid already exists.');
    return; // Abort the transaction.
  }
  }, function (error, committed, snapshot) {
    if (committed) {
      console.log('start a new transaction');
      ref.child('groups').child(groupid).child(userid).tranaction(function (currentData) {
        if (currentData === null) {
            return userid;
        } else {
            console.log('Userid already exists.');
            //add code here to roll back the groupid added to users
            return; // Abort the transaction.
        }
      }, function (error, committed, snapshot) {
         if (error) {
             //rollback the groupid that was added to users in previous transaction
         }
      })
  }
});