`ToOne.targetId` changes when it shouldn't

[nikitadol]

Is there an existing issue?

• I have searched existing issues

Build info

• objectbox version: 4.3.0
• Flutter/Dart version: 3.29.3 / 3.7.2
• Build OS: macOS 15.5
• Deployment OS or device: Any

Expected behavior

ToOne.target will be valid if the model was deleted and then added again with the same Id

Actual behavior

If I delete the model that I added to ToOne.target and then add it again, the link refers to an unknown id, although it is the same

Code

Code

import 'package:flutter/widgets.dart';
import 'package:objectbox/objectbox.dart';

import 'objectbox.g.dart';

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();

  final Store store = await openStore();

  final modelABox = store.box<ModelA>();
  final modelBBox = store.box<ModelB>();

  modelABox.removeAll();
  modelBBox.removeAll();

  final modelAId = '321';
  print(fastHash(modelAId)); // 3305779717846957101

  print(
    modelBBox.put(ModelB()..modelA.target = ModelA(id: modelAId)),
  ); // auto inc id
  print(modelABox.put(ModelA(id: modelAId))); // 3305779717846957101

  print(modelBBox.getAll().first.modelA.targetId); // 3305779717846957101
  print(modelBBox.getAll().first.modelA.target); // Instance of 'ModelA'

  print(modelABox.remove(fastHash(modelAId))); // true

  print(modelBBox.getAll().first.modelA.targetId); // 3305779717846957101
  print(modelBBox.getAll().first.modelA.target); // null

  print(modelABox.put(ModelA(id: modelAId))); // 3305779717846957101

  print(
    modelBBox.getAll().first.modelA.targetId,
  ); // 3305779715767271424 <- ?????????????
  print(modelBBox.getAll().first.modelA.target); // null
}

/// FNV-1a 64bit hash algorithm optimized for Dart Strings
int fastHash(String string) {
  var hash = 0xcbf29ce484222325;

  var i = 0;
  while (i < string.length) {
    final codeUnit = string.codeUnitAt(i++);
    hash ^= codeUnit >> 8;
    hash *= 0x100000001b3;
    hash ^= codeUnit & 0xFF;
    hash *= 0x100000001b3;
  }

  return hash;
}

@Entity()
class ModelA {
  @Id(assignable: true)
  int dbId;

  @Index()
  String id;

  ModelA({required this.id}) : dbId = fastHash(id);
}

@Entity()
class ModelB {
  @Id()
  int dbId;

  final modelA = ToOne<ModelA>();

  ModelB({this.dbId = 0});
}

Logs, stack traces

Logs

flutter: 3305779717846957101
flutter: 25
flutter: 3305779717846957101
flutter: 3305779717846957101
flutter: Instance of 'ModelA'
flutter: true
flutter: 3305779715767271424
flutter: null
flutter: 3305779717846957101
flutter: 3305779715767271424
flutter: null

[greenrobot-team]

Thanks for reporting!

It appears that for such a large @Id value when removing a target object, the target object ID is not correctly set to 0.

You can make above example work as expected by using a smaller ID for ModelA, like 33057797.

So to summarize: the targetId is expected to change when the target object is removed. But it should change to 0 and not to some other value.

For our reference, this is internal issue objectbox-dart#151.

[nikitadol]

Thanks for the answer!

If when inserting values into Store there is no check whether targetId is valid, then is it possible to get a behavior where targetId will not be set to 0 when deleting? (ToOne assumes that it may be absent -_ToOneState.unresolvable)

[greenrobot-team]

then is it possible to get a behavior where targetId will not be set to 0 when deleting?

When removing an object, the database checks if its ID is used in any relations and removes it from them.

But if your code sets a targetId that does not exist, there is also no object with that ID that can be deleted? So technically this can be answered with no.