No change notification about a child RealmObject change.

[serhii-k]

What happened?

I've encountered this bug with a device synced realm but replicated it in a simple local-only example.

Let's say our schema contains three RealmModels:

• B, which has an integer value
• A, which holds an instance of B b
• Folder, which contains a List<A> list

In our realm, we have one instance of each:

• We've added an instance of A (with its B instance).
• And we've put this A instance into the list inside a Folder instance.

Also, we are listening to the following changes:

• folder.changes
• folder.list.changes
• a.changes

Now, when we modify the value inside a.b:

• only folder.list.changes is triggered 😞
• but NOT a.changes

Please see the full example to understand the problem more clearly.

Repro steps

1. schemas.dart

import 'package:realm/realm.dart';

part 'schemas.realm.dart';

@RealmModel()
class _Folder {
  @PrimaryKey()
  @MapTo('_id')
  late ObjectId id;

  late List<_A> list;
}

@RealmModel()
class _A {
  @PrimaryKey()
  @MapTo('_id')
  late ObjectId id;

  late _B? b;
}

@RealmModel()
class _B {
  @PrimaryKey()
  @MapTo('_id')
  late ObjectId id;

  late int value;
}

2. main.dart

// ignore_for_file: avoid_print

import 'package:buggy/schemas.dart';
import 'package:flutter/material.dart';
import 'package:realm/realm.dart';

Future<void> main() async {
  final config = Configuration.local([
    A.schema,
    B.schema,
    Folder.schema,
  ]);
  Realm.deleteRealm(config.path); // Just to clear all data
  final realm = Realm(config);

  realm.write(() {
    final a = realm.add(A(
      ObjectId.fromValues(0, 0, 0),
      b: B(ObjectId.fromValues(0, 0, 1), 0),
    ));
    realm.add(Folder(ObjectId.fromValues(0, 0, 2), list: [a]));
  });

  // Find the objects.
  final a = realm.find<A>(ObjectId.fromValues(0, 0, 0))!;
  final b = a.b!;
  final folder = realm.find<Folder>(ObjectId.fromValues(0, 0, 2))!;

  // Subscribe to the changes.
  folder.changes.listen((_) => print('Folder changed'));
  folder.list.changes.listen((_) => print('Folder.list changed'));
  a.changes.listen((_) => print('A changed'));

  await Future.delayed(const Duration(milliseconds: 1000));
  print('* b.value = 1');
  realm.write(() => b.value = 1);

  await Future.delayed(const Duration(milliseconds: 1000));
  print('* b.value = 2');
  realm.write(() => b.value = 2);

  await Future.delayed(const Duration(milliseconds: 1000));
  print('* Done.');
  print('---------');
  print('Problem');
  print('??? Where is "A changed" after its b was modified ???');
  print('??? If the Folder.list was triggered, why A was not ???');

  realm.close();

  runApp(const MaterialApp(home: Scaffold()));
}

The output

I/flutter (26316): Folder changed
I/flutter (26316): Folder.list changed
I/flutter (26316): A changed
I/flutter (26316): * b.value = 1
I/flutter (26316): Folder.list changed
I/flutter (26316): * b.value = 2
I/flutter (26316): Folder.list changed
I/flutter (26316): * Done.
I/flutter (26316): ---------
I/flutter (26316): Problem
I/flutter (26316): ??? Where is "A changed" after its b was modified ???
I/flutter (26316): ??? If the Folder.list was triggered, why A was not ???

Version

3.3.0

What Atlas Services are you using?

Atlas Device Sync

What type of application is this?

Flutter Application

Client OS and version

Android 14 (SDK 34)

Code snippets

No response

Stacktrace of the exception/crash you're getting

No response

Relevant log output

No response

[sync-by-unito[bot]]

➤ PM Bot commented:

Jira ticket: RDART-1073

[serhii-k]

It turns out that it was implemented this way to optimize performance.

And there is another method, changesFor([keyPaths]), which takes into account how deep you want to observe changes. So it's possible to specify the following keyPaths:

• b.value to trigger changes if b.value was changed
• b.* if any property of b was changed
• *.* if any property of any linked object was changed
• etc.

a.changesFor(['*', 'b.value']).listen((changes) => print('B changed ${changes.properties}'));

[serhii-k]

So, the only request about this ticket is to please mention the correct way to register a RealmObject Change Listener here:

https://www.mongodb.com/docs/atlas/device-sdks/sdk/flutter/realm-database/react-to-changes/#register-a-realmobject-change-listener

There is no any bug here. Realm is soooooo COOL! 🤩

[nielsenko]

@serhii-k Just back from vacation. Happy you worked it out 👍