Problem while handling simultaneous updates in realtime database firebase

Question

I am new to mobile android development. I am trying to build an library management application. Here I have two admins ,who can modify the database (realtime database, firebase).I tried the following code to handle the case when both admins try to alter the database simultaneously:

  int books= Integer.parseInt(addBooks.getText().toString());
  String isbn=isbnNo.getText().toString();
 DatabaseReference ref=reference.child("books").child(isbn).child("bookCount");
 ref.runTransaction(new Transaction.Handler() {
     @NonNull
     @Override
     public Transaction.Result doTransaction(@NonNull MutableData  mutableData) {
         Integer currentBookCount=mutableData.getValue(Integer.class);
         mutableData.setValue(currentBookCount+books);
         return Transaction.success(mutableData);
     }

     @Override
     public void onComplete(@Nullable DatabaseError error, boolean committed, @Nullable DataSnapshot currentData) {
         Toast.makeText(getApplicationContext(),"Added successfully",Toast.LENGTH_LONG).show();
     }
 });

My database looks like this:

this

It shows "Added successsfully" messages in both the devices when I run simultaneously, but is not upadating the final answer in the database.I am also not sure if this approach is appropriate, any help is appreciated.

Transactions can fail, and you're ignoring that case right now in your code. Can you check if `error` has a value in `onComplete`? — Frank van Puffelen, Mar 26 '21 at 18:44

score 0 · Accepted Answer · answered Mar 26 '21 at 18:47

0

If you want to do a simple increment (or decrement) operation, Firebase has a much easier solution for that these days with a built in increment() operation.

For that it is important that you store the value as a number though, and not as a string as you have it now. Once you store it as a number, you can increment the bookCount by books with:

int books= Integer.parseInt(addBooks.getText().toString());
String isbn=isbnNo.getText().toString();
DatabaseReference ref=reference.child("books").child(isbn).child("bookCount");
ref.setValue(ServerValue.increment(books));

Also see:

How quickly can you atomically increment a value on the Firebase Realtime Database? for a performance comparison between using a runTransaction and increment.

answered Mar 26 '21 at 18:47

Frank van Puffelen

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Thanks, this solution works. I also want to add one more condition that the bookCount shouldn't exceed 100. Is it possible to add such condition by using ServerValue.increment()? – Bhanu Mar 27 '21 at 09:39
Not in the code itself, but you could do that in the server-side security rules. See https://firebase.google.com/docs/firestore/security/rules-conditions#data_validation. If you're having trouble making that work, I'd recommend posting a new question with its own reproduction. – Frank van Puffelen Mar 27 '21 at 14:23

Problem while handling simultaneous updates in realtime database firebase

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