Flutter ObjectBox - Can't generate DB model with custom class

Question

Following the NoSQL Database Storage | Flutter ObjectBox (vs Sqlite, Sqflite, Hive), I am trying to setup an ObjectBox database with multiple classes. I currently have the following classes,

Exercise.dart

import 'package:objectbox/objectbox.dart';

@Entity()
@Sync()
class Exercise {
  int? id;
  final String? name;
  final String? target;
  final String? bodyPart;
  final String? equipment;
  final String? gifUrl;

   Exercise({
    this.id = 0,
    required this.name,
    required this.target,
    required this.bodyPart,
    required this.equipment,
    required this.gifUrl,
  });

  factory Exercise.fromJson(Map<String, dynamic> json) {
    return Exercise(
        id: int.tryParse(json['id'].toString()),
        name: json["name"].toString(),
        target: json["target"].toString(),
        bodyPart: json["bodyPart"].toString(),
        equipment: json["equipment"].toString(),
        gifUrl: json["gifUrl"].toString());
  }
}

and
Set.dart

import 'package:objectbox/objectbox.dart';
import 'package:pump_that_iron/models/exercise.dart';

@Entity()
@Sync()
class Set {
  int? id;
  final Exercise? exercise;
  final int? repetitions;

  Set({
    this.id = 0,
    required this.exercise,
    required this.repetitions,
  });
}

From these classes I am trying to build a model class using ObjectBox and the flutter pub run build_runner build command. However, whenever that command is run, I get the following error,

Cannot use the default constructor of 'Set': don't know how to initialize param exercise - no such property.

as well as

[WARNING] objectbox_generator:resolver on lib/models/set.dart: skipping property 'exercise' in entity 'Set', as it has an unsupported type: 'Exercise?'

Initially, when running the build command with the Exercise.dart being the only present class, it is successful. However, as soon as I add the Set.dart file containing the Exercise class as a variable, I am no longer able to build. Another thing to note, is that when the Exercice variable is omitted from the Set class, it runs successfully.

I found the following How initialize Objectbox entity with custom type? SO thread with a similar problem and tried to replicate the steps by,

1. Adding a getExercise getter in the Set.dart class and adding it to the constructor

Set({
    this.id = 0,
    this.exercise = getExercise,
    required this.repetitions,
  });

  get getExercise => Exercise(
      name: "name",
      target: "target",
      bodyPart: "bodyPart",
      equipment: "equipment",
      gifUrl: "gifUrl");

2. This required me to make the Exercise.dart constructor constant, and making the following changes

class Exercise {
  @Id(assignable: true)
  final int? id;
  ...

  const Exercise({
    this.id = 0,
    ...
  });

This is now giving me a The default value of an optional parameter must be constant. error when trying to set the exercise variable at this.exercise = getExercise. I tried following the instructions from another SO thread Default values of an optional parameter must be constant, but I am still having issues.

I was wondering if anybody could help me set up my database and explain what is going wrong. Any help is appreciated.

Thank you.

Answer 1

ObjectBox just supports storing some base types by default. For custom types you have to either map them to a supported type, or I assume what you are looking for in this case create a relation to an @Entity class:

@Entity()
class Set {
  int? id;
  final exercise = ToOne<Exercise>();
  final int? repetitions;
}

// To change the ToOne target:
set.exercise.target = Exercise();