Firebase Realtime Database Transaction

Question

I have been trying to run the transaction method but it fails to both get and set proper data in the Firebase Realtime Database.

Following is the code:

 private void receiveMoney() {
    String mobile=recipientText.getText().toString().trim();
    Double amount=Double.parseDouble(amountText.getText().toString().trim());
    mDatabase3=FirebaseDatabase.getInstance().getReference("account_details/Gn2eRixQQiTpvhX870n6nZp66tO2");
    mDatabase3.runTransaction(new Transaction.Handler() {

        @NonNull
        @Override
        public Transaction.Result doTransaction(@NonNull MutableData currentData) {

            Double newBalance=(double) currentData.child("initialBalance").getValue();
            System.out.println("Current Balance: "+newBalance+"  Amount: "+amount);

            currentData.setValue(newBalance);
            return Transaction.success(currentData);
        }

        @Override
        public void onComplete(@Nullable  DatabaseError error, boolean committed, @Nullable DataSnapshot currentData) {

        }
    });
}

Following is my database: Database Screenshot

Following is the error I get in the Run log:

E/RepoOperation: Caught Throwable.
java.lang.NullPointerException: Attempt to invoke virtual method 'double java.lang.Double.doubleValue()' on a null object reference
    at com.example.efikas.SendMoneyActivity$1.doTransaction(SendMoneyActivity.java:86)
    at com.google.firebase.database.core.Repo.startTransaction(Repo.java:933)
    at com.google.firebase.database.DatabaseReference$4.run(DatabaseReference.java:492)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:458)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:301)
    at java.util.concurrent.ThreadPoolExecutor.processTask(ThreadPoolExecutor.java:1187)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1152)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
    at java.lang.Thread.run(Thread.java:784)

enter code here

E/RepoOperation: Caught Throwable. java.lang.NullPointerException: Attempt to invoke virtual method 'double java.lang.Double.doubleValue()' on a null object reference @TicherhazFreePalestine — yuri yuna, Oct 02 '21 at 09:08
The value that you store is not `double`. Can you change the value to 1000.00 ? — Ticherhaz FreePalestine, Oct 02 '21 at 09:11
It remains the same,sir. The value pushed into the database is double. @TicherhazFreePalestine — yuri yuna, Oct 02 '21 at 09:17
@TicherhazFreePalestine I have only declared the database reference before. And initialized here. — yuri yuna, Oct 02 '21 at 10:01
@TicherhazFreePalestine, Thank you so much for your help. I did try it. However, it catches another null exception for some reason. — yuri yuna, Oct 02 '21 at 11:37

score 2 · Accepted Answer · answered Oct 02 '21 at 11:09

2

To increment the value of initialBalance with the value of amount, there is no need to use any transaction. You can simply increment the value using the following lines of code:

DatabaseReference db = FirebaseDatabase.getInstance().getReference();
DatabaseReference initialBalanceRef = db
    .child("account_details")
    .child("Gn2eRixQQiTpvhX870n6nZp66tO2")
    .child("initialBalance");
initialBalanceRef.setValue(ServerValue.increment(amount));

That's it. If you still want to use a transaction, please check my answer from the following post:

How to save users score in firebase and retrieve it in real-time in Android studio

answered Oct 02 '21 at 11:09

Alex Mamo

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Thank you so much, sir! This works fine. However, could you tell me if it works the same as the transaction method? I am working on a demo e-wallet. So if multiple users push balance at the same time would it still increment data properly? – yuri yuna Oct 02 '21 at 11:36
1

Yes, it works exactly like that. You'll always have consistent data. The difference is that you don't have a round trip to the server and back. You get increment it instantly. – Alex Mamo Oct 02 '21 at 11:38
1

Done, Sir! Thank you so much to you all! Have a good day! – yuri yuna Oct 02 '21 at 11:44

score 1 · Answer 2 · answered Oct 02 '21 at 09:27

I think because you are using runTransaction and I think you should focus only 1 thing.

mDatabase3=FirebaseDatabase.getInstance().getReference("account_details/Gn2eRixQQiTpvhX870n6nZp66tO2/initialBalance");
mDatabase3.runTransaction(new Transaction.Handler() {

    @NonNull
    @Override
    public Transaction.Result doTransaction(@NonNull MutableData currentData) {
        if (currentData.getValue() == null) {
            currentData.setValue(0);
        } else {
            Double newBalance= (Double) currentData.getValue();
            System.out.println("Current Balance: "+newBalance+"  Amount: "+amount);

            currentData.setValue(newBalance);
        }
        

        return Transaction.success(currentData);
    }

    @Override
    public void onComplete(@Nullable  DatabaseError error, boolean committed, @Nullable DataSnapshot currentData) {

    }
});

Firebase Realtime Database Transaction

2 Answers2