Firebase - Multiple users simultaneously updating same object using its old value

Question

I\'m keeping track of a count that users update on the Firebase database through an Android app. The way it works right now is that upon interaction the user\'s app looks up

Answer 1

When working with complex data that could be corrupted by concurrent modifications, such as incremental counters, Firebase provides a transaction operation.

You give this operation two arguments: an update function and an optional completion callback. The update function takes the current state of the data as an argument and will return the new desired state you would like to write.

For example, if we wanted to increment the number of upvotes on a specific blog post, we would write a transaction like the following (Legacy code):

    Firebase upvotesRef = new Firebase("https://docs-examples.firebaseio.com/android/saving-data/fireblog/posts/-JRHTHaIs-jNPLXOQivY/upvotes");
upvotesRef.runTransaction(new Transaction.Handler() {
    @Override
    public Transaction.Result doTransaction(MutableData currentData) {
        if(currentData.getValue() == null) {
            currentData.setValue(1);
        } else {
            currentData.setValue((Long) currentData.getValue() + 1);
        }
        return Transaction.success(currentData); //we can also abort by calling Transaction.abort()
    }
    @Override
    public void onComplete(FirebaseError firebaseError, boolean committed, DataSnapshot currentData) {
        //This method will be called once with the results of the transaction.
    }
});

Legacy source

New firebase version source

Answer 2

Firebase database handles up to 100 simultaneous real time connections to your database if your are using their free plan but once the 101st users connects to your database the database would stop responding and would display the values that were last edited. Firebase is really good at handling real time connections simultaneously so it depends on your pricing plans. If you want to use the database for free, there will be no issues handling 100 connections but if you want to handle more users use their generous pricing plans.