[cloud-firestore] Unable to set in a Firestore transaction if the collection does not exist.

[FranRiadigos]

Hi, struggling a lot with this.

Issue

The following transaction fails if the root collection unpublished does not exist.
Otherwise, if that collection exists it works.

Eventually, the unpublished collection may have no items if all of them have been published.
Then, if this unpublished collection has no elements on it, Firebase deletes the collection automatically.

Code

Path: root collection / id / sub-collection / id

Future update(String itemId) 
{
      final ref = db.collection('unpublished').doc('cityId').collection('items').doc('itemId');
      
      await db.runTransaction((transaction) async {
            // Gets the document if any
            final item = await transaction.get(ref);
      
            // Update just some fields
            if (document.exists) {

              // Make sure there is no pending changes
              final hasChanged = item.updatedDate > lastUpdatedDate;
              // In case of any changes 
              if (hasChanged) throw 'Has changes';

              // Otherwise, update
              final json = ...;
              transaction.set(item, json, SetOptions(merge: true));
            }
            //  Create the document with all fields
            else {
              final json = ...;
              transaction.set(item, json); <-- this fails, due to exhausted retries 
            }
      });
}

I figured out the transaction was failing (retrying all time) if the root collection or the sub-collection did not exist.

Using a different structure with a flag field and avoiding the unpublished collection is not an option for me, and I have no idea what to do to solve this.

Any help is much appreciated.

[FranRiadigos]

Never mind.

It seems to be happening only with the emulator.