[cloud_firestore]: Snapshot drops field from set() when followed by update() with pending writes

[lukyanov]

Is there an existing issue for this?

• I have searched the existing issues.

Which plugins are affected?

Cloud Firestore

Which platforms are affected?

iOS

Description

When a document is created with docRef.set() and then docRef.update() is called on the same document before the set() is confirmed by the server, snapshot listeners drop a field from the optimistic state reconstruction.

Expected: all fields from the original set() should be present in the snapshot, merged with any pending update() mutations.

Actual: a plain string field is completely absent from the snapshot data — not even present in map.keys — even though:

• The field was confirmed present in the data passed to set() (logged immediately before the call)
• A direct doc.get(GetOptions(source: Source.server)) confirms the server has the field
• No update() call ever touches or deletes that field
• Other plain fields from the same set() call are preserved correctly

Diagnostic metadata on the broken snapshot:

• doc.metadata.hasPendingWrites = true
• doc.metadata.isFromCache = false

Reproducing the issue

final docRef = FirebaseFirestore.instance.collection('items').doc();

// 1. Create document with set(), do not await
unawaited(docRef.set({
  'ownerId': 'user_123',
  'title': 'Test item',
  'createdAt': FieldValue.serverTimestamp(),
  'status': 0,
}));

// 2. Call update() before the server confirms the set()
await Future.delayed(Duration(milliseconds: 100));
await docRef.update({
  'retryCount': 1,
  'errorMessage': FieldValue.delete(),
});

// 3. A default-source snapshot listener on a query covering this document
//    returns the doc with 'ownerId' missing from the data map.
FirebaseFirestore.instance
    .collection('items')
    .orderBy('createdAt', descending: true)
    .snapshots()
    .listen((snapshot) {
  for (final doc in snapshot.docs) {
    final data = doc.data();
    // 'ownerId' is missing from data.keys entirely
    print('ownerId: ${data['ownerId']}');  // null
    print('title: ${data['title']}');      // 'Test item' ✓
    print('status: ${data['status']}');    // 0 ✓

    // Direct server fetch confirms the field exists
    doc.reference.get(GetOptions(source: Source.server)).then((serverDoc) {
      print('server ownerId: ${serverDoc.data()?['ownerId']}');  // 'user_123' ✓
    });
  }
});

Firebase Core version

4.4.0

Flutter Version

3.38.9

Relevant Log Output

# set() data includes ownerId
[DIAG] ownerId=user_123, data={ownerId: user_123, title: Test item, createdAt: FieldValue(...), status: 0}

# Snapshot listener: ownerId not in keys
[DIAG] ownerId missing, hasPendingWrites=true, isFromCache=false, keys=[title, retryCount, createdAt, status]

# Direct server fetch: ownerId present
[DIAG] server doc: exists=true, ownerId=user_123, keys=[ownerId, title, retryCount, createdAt, status]

Flutter dependencies

Expand Flutter dependencies snippet

Dart SDK 3.10.8
Flutter SDK 3.38.9

- cloud_firestore 6.1.2
- firebase_core 4.4.0
- _flutterfire_internals 1.3.66
- cloud_firestore_platform_interface 7.0.6
- cloud_firestore_web 5.1.2

Additional context and comments

The server data is correct, so the issue is purely in the client-side optimistic state reconstruction. Subsequent snapshots (once all pending writes are confirmed) include the field correctly.

• Firestore offline persistence is enabled
• Tested on iOS physical device
• ListenSource.cache queries correctly show the field — only default-source snapshot listeners are affected

[lukyanov]

Filed upstream on the native iOS SDK: firebase/firebase-ios-sdk#15864