firebase - Data in transaction is null

Question

I have a problem with transactions. The data in the transaction is always null and the update handler is called only singe once. The documentation says :

To accomplish this, you pass transaction() an update function which is used to transform the current value into a new value. If another client writes to the location before your new value is successfully written, your update function will be called again with the new current value, and the write will be retried. This will happen repeatedly until your write succeeds without conflict or you abort the transaction by not returning a value from your update function

Now I know that there is no other client accessing the location right now. Secondly if I read the documentation correctly the updateCounters function should be called multiple times should it fail to retrieve and update data.

The other thing - if I take out the condition if (counters === null) the execution will fail as counters is null but on a subsequent attempt the transaction finishes fine - retrieves data and does the update.

simple once - set on this location work just fine but it is not safe.

Please what do I miss?

here is the code

self.myRef.child('counters')
  .transaction(function updateCounters(counters){
    if (counters === null) {
      return;
    }
    else {
      console.log('in transaction counters:', counters);
      counters.comments = counters.comments + 1;
      return counters;
    }
  }, function(error, committed, ss){
    if (error) {
      console.log('transaction aborted');
      // TODO error handling
    } else if (!committed){
      console.log('counters are null - why?');
    } else {
      console.log('counter increased',ss.val());
    }
  }, true);

here is the data in the location

counters:{
  comments: 1,
  alerts: 3,
  ...
}

Answer 1

Waitting for answers