Can not load ToMany data content

[ThatPham2000]

Is there an existing issue?

No

• [ √ ] I have searched existing issues

Build info

• objectbox version: 4.0.1
• Flutter/Dart version: 3.22.2
• Build OS: macOS Ventura 13.6.1
• Deployment OS or device: Android 12 emulator

Steps to reproduce

Just run this code:

  int _counter = 0;

  final boxA = objectbox.store.box<A>();
  final boxB = objectbox.store.box<B>();
  final boxC = objectbox.store.box<C>();

  void _incrementCounter() {
    final a = A.fromJson({
      'name': 'Name A',
      'b': {
        'c': [
          {
            'name3': 'Name 3A',
          },
          {
            'name3': 'Name 3B',
          },
        ],
      }
    });

    // save c
    boxC.putMany(a.b.target!.c);

    // save b
    boxB.put(a.b.target!);

    // save a
    boxA.put(a);

    final aFromDb = boxA.getAll();
    final bFromA = aFromDb.first.b.target;
    final cFromB = bFromA!.c;

    final bFromDb = boxB.getAll();
    final cFromDb = boxC.getAll();

    setState(() {
      _counter++;
    });
  }

Expected behavior

I want to get a list of "c" from "a".

Actual behavior

Get "c" from "a" is empty.

Code

Code

import 'package:json_annotation/json_annotation.dart';
import 'package:objectbox/objectbox.dart';

part 'model.g.dart';

@Entity()
@JsonSerializable(explicitToJson: true)
class A {
  A({required this.name, required this.b}) {
    obId = name.hashCode;
  }

  @Id(assignable: true)
  @JsonKey(includeFromJson: false, includeToJson: false)
  int? obId;

  final String name;

  @_ToOneConverter()
  final ToOne<B> b;

  factory A.fromJson(Map<String, dynamic> json) => _$AFromJson(json);

  Map<String, dynamic> toJson() => _$AToJson(this);
}

@Entity()
@JsonSerializable(explicitToJson: true)
class B {
  B({required this.c}) {
    obId = c.map((element) => element).toList().hashCode;
  }

  @Id(assignable: true)
  @JsonKey(includeFromJson: false, includeToJson: false)
  int? obId;

  @_ToManyConverter()
  final ToMany<C> c;

  factory B.fromJson(Map<String, dynamic> json) => _$BFromJson(json);

  Map<String, dynamic> toJson() => _$BToJson(this);
}

@Entity()
@JsonSerializable(explicitToJson: true)
class C {
  C({required this.name3}) {
    obId = name3.hashCode;
  }

  @Id(assignable: true)
  @JsonKey(includeFromJson: false, includeToJson: false)
  int? obId;

  final String name3;

  factory C.fromJson(Map<String, dynamic> json) => _$CFromJson(json);

  Map<String, dynamic> toJson() => _$CToJson(this);
}

class _ToOneConverter
    implements JsonConverter<ToOne<B>, Map<String, dynamic>?> {
  const _ToOneConverter();

  @override
  ToOne<B> fromJson(Map<String, dynamic>? json) => ToOne<B>(
        target: json == null ? null : B.fromJson(json),
      );

  @override
  Map<String, dynamic>? toJson(ToOne<B> rel) => rel.target?.toJson();
}

class _ToManyConverter implements JsonConverter<ToMany<C>, List<dynamic>?> {
  const _ToManyConverter();

  @override
  ToMany<C> fromJson(List<dynamic>? json) => ToMany<C>(
        items: json?.map((e) => C.fromJson(e)).toList(),
      );

  @override
  List<Map<String, dynamic>>? toJson(ToMany<C> rel) =>
      rel.map((obj) => obj.toJson()).toList();
}

import 'package:flutter/material.dart';
import 'package:object_box_to_many/model/object_box.dart';

import 'model/model.dart';

late ObjectBox objectbox;

void main() async {
  WidgetsFlutterBinding.ensureInitialized();

  objectbox = await ObjectBox.create();

  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  final boxA = objectbox.store.box<A>();
  final boxB = objectbox.store.box<B>();
  final boxC = objectbox.store.box<C>();

  void _incrementCounter() {
    final a = A.fromJson({
      'name': 'Name A',
      'b': {
        'c': [
          {
            'name3': 'Name 3A',
          },
          {
            'name3': 'Name 3B',
          },
        ],
      }
    });

    // save c
    boxC.putMany(a.b.target!.c);

    // save b
    boxB.put(a.b.target!);

    // save a
    boxA.put(a);

    final aFromDb = boxA.getAll();
    final bFromA = aFromDb.first.b.target;
    final cFromB = bFromA!.c;

    final bFromDb = boxB.getAll();
    final cFromDb = boxC.getAll();

    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headlineMedium,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ),
    );
  }
}

name: object_box_to_many
description: A new Flutter project.
# The following line prevents the package from being accidentally published to
# pub.dev using `flutter pub publish`. This is preferred for private packages.
publish_to: 'none' # Remove this line if you wish to publish to pub.dev

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number is used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
# In Windows, build-name is used as the major, minor, and patch parts
# of the product and file versions while build-number is used as the build suffix.
version: 1.0.0+1

environment:
  sdk: '>=3.1.0 <4.0.0'

# Dependencies specify other packages that your package needs in order to work.
# To automatically upgrade your package dependencies to the latest versions
# consider running `flutter pub upgrade --major-versions`. Alternatively,
# dependencies can be manually updated by changing the version numbers below to
# the latest version available on pub.dev. To see which dependencies have newer
# versions available, run `flutter pub outdated`.
dependencies:
  flutter:
    sdk: flutter
  objectbox: ^4.0.1
  objectbox_flutter_libs: any
  path: any
  json_annotation: ^4.8.1


  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^1.0.2

dev_dependencies:
  flutter_test:
    sdk: flutter
  build_runner: ^2.0.0
  objectbox_generator: any
  json_serializable: ^6.2.0

  # The "flutter_lints" package below contains a set of recommended lints to
  # encourage good coding practices. The lint set provided by the package is
  # activated in the `analysis_options.yaml` file located at the root of your
  # package. See that file for information about deactivating specific lint
  # rules and activating additional ones.
  flutter_lints: ^2.0.0

# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec

# The following section is specific to Flutter packages.
flutter:

  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true

  # To add assets to your application, add an assets section, like this:
  # assets:
  #   - images/a_dot_burr.jpeg
  #   - images/a_dot_ham.jpeg

  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.dev/assets-and-images/#resolution-aware

  # For details regarding adding assets from package dependencies, see
  # https://flutter.dev/assets-and-images/#from-packages

  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #
  # For details regarding fonts from package dependencies,
  # see https://flutter.dev/custom-fonts/#from-packages

Logs, stack traces

TODO Add relevant logs, a stack trace or crash report.

Logs

[Paste your logs here]

[greenrobot-team]

Is this maybe because the ToMany b.c is loaded on first access?

If not, then the relation of "b" is not updated. I would welcome a simple example project to reproduce it.

Anyhow, I strongly recommend to use a separate model for JSON and for ObjectBox and map between them. Otherwise, future changes may be difficult or impossible.

Also: please don't post screenshots, post actual code.

[ThatPham2000]

Also: I provided all of my code. You can copy and run.

[greenrobot-team]

Oh, sorry I did not see the collapsed code block. I updated the description with the actual code that can be copied. I will have a look once I have time.

Anyhow, my question is still valid. Including the note about model separation.

[ThatPham2000]

The problem is that my model (not mock ones here) is built based on API so I need to parse from JSON here.

[greenrobot-team]

The problem is that my model (not mock ones here) is built based on API so I need to parse from JSON here.

Sure. But your project should then still have a separate model for the database. So one for JSON parsing and one for the database. Then map between those.

[greenrobot-team]

The underlying issue is that the constructor for B accesses the ToMany:

  B({required this.c}) {
    obId = c.map((element) => element).toList().hashCode;
  }

This breaks the ToMany as it is initialized only after this. See the generated code:

          final cParam = obx.ToMany<C>();
          final object = B(c: cParam)
            ..obId =
                const fb.Int64Reader().vTableGetNullable(buffer, rootOffset, 4);
          obx_int.InternalToManyAccess.setRelInfo<B>(
              object.c, store, obx_int.RelInfo<B>.toMany(1, object.obId!));
          return object;

We might be able to change the generated code to call setRelInfo before passing the ToMany to the object.

[ThatPham2000]

Thanks for your update.
so what is the solution for duplicate objects in case I do not assign object box id by myself (assignable: true).
Because when I call the API many times, we have a lot of duplicate objects with the same values.

[greenrobot-team]

The above issue only exists when reading from a Box. The data is correctly put. Maybe you can change the model to provide a default, no arguments constructor that ObjectBox can use.

Or as I said, do not use the same model for your network layer (JSON) and the database layer.