How can I create a incremental ID for Firebase realtime database?

Question

So in my realtime database it would look like:

ss: {
  xx: {
    id: 1
  },
  yy: {
    id: 2
  },
  ...
}

I tried to first get child with largest ID FirebaseRef.child('ss').orderByChild('id').limitToLast(1) and then do +1 for retrieved value.. then push new record with that. But that could result doubling id's, as between the fetch and the push, someone else can make a new record. I looked into transaction feature, but could not figure out have to use that in my scenario (as it retrieves and updates only values?).

I've never looked into Firebase, but does it support sequences? Normal RDBMSes usually have this - it's basically something that gives you incrementing (or otherwise defined) numbers for use as IDs. The DB handles this automatically on insert, so you never need to handle it manually. — VLAZ, Jan 05 '20 at 20:13
Could not find anything on that. That's why I'm asking here. Thank you. — trshmanx, Jan 05 '20 at 20:14
Also see: https://stackoverflow.com/a/47653231, https://stackoverflow.com/a/39065899, https://stackoverflow.com/a/36682658, https://stackoverflow.com/a/58050877 — Frank van Puffelen, Jan 05 '20 at 21:57

score 1 · Accepted Answer · answered Jan 05 '20 at 20:22

1

One possible approach is to maintain a counter and each time you need to generate a new id, increment this counter in a transaction and read the value:

The following should do the trick:

  //Declare a function that increment a counter in a transaction
  function getId() {
    var counterRef = firebase.database().ref('counter');
    return counterRef.transaction(function(currentId) {
      return currentId + 1;
    });
  }


  //Call the asynchronous getID() function
  getId().then(function(transactionResult) {
    var newId = transactionResult.snapshot.val();
    console.log(newId);
    firebase.database().ref('ss/xx').set({id: newId});
  });

You don't need to create the counter node, it will be automatically created with the first call to the getId() function.

answered Jan 05 '20 at 20:22

Renaud Tarnec

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Are you sure `return currentId + 1;` is enough in the absence of a counter? I'd usually do `return (currentId || 0) + 1;`. – Frank van Puffelen Jan 05 '20 at 21:57
@FrankvanPuffelen It is done this way in the example from the [documentation](https://firebase.google.com/docs/reference/js/firebase.database.Reference?authuser=2#transaction) and it is expressly mentioned "// If users/ada/rank has never been set, currentRank will be `null`". – Renaud Tarnec Jan 05 '20 at 22:00
1

That part I know. But I never realized that `null + 1 = 1`. Oh JavaScript, you wonderful beast. :-D – Frank van Puffelen Jan 05 '20 at 22:04
1

`true + null = 1` is also an "interesting" one... :-) – Renaud Tarnec Jan 05 '20 at 22:08

How can I create a incremental ID for Firebase realtime database?

1 Answers1