json_serializable 的复杂模型 - 列表 <objects> 未转换为地图

Question

更新我构建了一个小示例，并将所有代码添加到此 post。我不得不相信这其中有一个 answer/explanation，我希望有人能告诉我我所缺少的东西。 Class 类型为对象的字段没有得到转换，我不明白为什么。

这是我正在使用的 classes 模型。

import 'package:json_annotation/json_annotation.dart';

part 'parent.g.dart';

@JsonSerializable()
class Parent {
  int id;
  final String name;
  final int age;
  List<Child> children;
  Job job;

  Parent({this.name, this.age, this.children, this.job});

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

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

@JsonSerializable()
class Child{
  int id;
  final String name;
  final int age;

  Child({this.name, this.age});

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

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

@JsonSerializable()
class Job{
  int id;
  String title;

  Job({this.title});

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

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

这是为这些 classes

生成的 .g 文件

// GENERATED CODE - DO NOT MODIFY BY HAND

part of 'parent.dart';

// **************************************************************************
// JsonSerializableGenerator
// **************************************************************************

Parent _$ParentFromJson(Map<String, dynamic> json) {
  return Parent(
    name: json['name'] as String,
    age: json['age'] as int,
    children: (json['children'] as List)
        ?.map(
            (e) => e == null ? null : Child.fromJson(e as Map<String, dynamic>))
        ?.toList(),
    job: json['job'] == null
        ? null
        : Job.fromJson(json['job'] as Map<String, dynamic>),
  )..id = json['id'] as int;
}

Map<String, dynamic> _$ParentToJson(Parent instance) => <String, dynamic>{
      'id': instance.id,
      'name': instance.name,
      'age': instance.age,
      'children': instance.children,
      'job': instance.job,
    };

Child _$ChildFromJson(Map<String, dynamic> json) {
  return Child(
    name: json['name'] as String,
    age: json['age'] as int,
  )..id = json['id'] as int;
}

Map<String, dynamic> _$ChildToJson(Child instance) => <String, dynamic>{
      'id': instance.id,
      'name': instance.name,
      'age': instance.age,
    };

Job _$JobFromJson(Map<String, dynamic> json) {
  return Job(
    title: json['title'] as String,
  )..id = json['id'] as int;
}

Map<String, dynamic> _$JobToJson(Job instance) => <String, dynamic>{
      'id': instance.id,
      'title': instance.title,
    };

这是父级 class

的 DAO class

import 'package:sembast/sembast.dart';

import 'package:json_serial_test/services/app_database.dart';
import 'package:json_serial_test/models/parent.dart';

class ParentDao {
  static const String PARENT_STORE_NAME = 'parents';
  // A Store with int keys and Map<String, dynamic> values.
  // This Store acts like a persistent map, values of which are Parent objects converted to Map
  final _parentStore = intMapStoreFactory.store(PARENT_STORE_NAME);

  // Private getter to shorten the amount of code needed to get the
  // singleton instance of an opened database.
  Future<Database> get _db async => await AppDatabase.instance.database;

  Future insert(Parent parent) async {
    await _parentStore.add(await _db, parent.toJson());
  }

  Future update(Parent parent) async {
    // For filtering by key (ID), RegEx, greater than, and many other criteria,
    // we use a Finder.
    final finder = Finder(filter: Filter.byKey(parent.id));
    await _parentStore.update(
      await _db,
      parent.toJson(),
      finder: finder,
    );
  }

  Future deleteAll() async {
    await _parentStore.delete(await _db);
  }

  Future delete(Parent parent) async {
    final finder = Finder(filter: Filter.byKey(parent.id));
    await _parentStore.delete(
      await _db,
      finder: finder,
    );
  }

  Future<List<Parent>> getAllSortedByName() async {
    // Finder object can also sort data.
    final finder = Finder(sortOrders: [
      SortOrder('name'),
    ]);

    final recordSnapshots = await _parentStore.find(
      await _db,
      finder: finder,
    );

    // Making a List<Parent> out of List<RecordSnapshot>
    return recordSnapshots.map((snapshot) {
      final parent = Parent.fromJson(snapshot.value);
      // An ID is a key of a record from the database.
      parent.id = snapshot.key;
      return parent;
    }).toList();
  }
}

这是我的测试

// Setup
          final k1 = Child(name: 'Billy', age: 10);
          final k2 = Child(name: 'Jannet', age: 9);
          final job = Job(title: 'Cook');
          final List<Child> kids = [k1, k2];

          final dad = Parent(name: 'Dave', age: 52, job: job, children: kids);

          await pDao.insert(dad);

          List<Parent> dadsInDb = await pDao.getAllSortedByName();

          print('Dads from DB: ${dadsInDb.toString()}');

在尝试将父项插入我的 sembast 数据库时，出现了这个错误。

E/flutter (12986): [ERROR:flutter/lib/ui/ui_dart_state.cc(157)] Unhandled Exception: Invalid argument(s): value Instance of 'Child' unsupported type Child E/flutter (12986): #0      cloneValue (package:sembast/src/utils.dart:191:3) E/flutter (12986): #1      cloneValue.<anonymous closure> (package:sembast/src/utils.dart:177:33) E/flutter (12986): #2      MappedListIterable.elementAt (dart:_internal/iterable.dart:417:29) E/flutter (12986): #3      ListIterable.toList (dart:_internal/iterable.dart:221:19) E/flutter (12986): #4      cloneValue (package:sembast/src/utils.dart:177:52) E/flutter (12986): #5      cloneValue.<anonymous closure> (package:sembast/src/utils.dart:174:49) E/flutter (12986): #6      MapMixin.map (dart:collection/maps.dart:165:28) E/flutter (12986): #7  cloneValue (package:sembast/src/utils.dart:173:18) E/flutter (12986):
#8      SembastStore.txnPutSync (package:sembast/src/store_impl.dart:133:15) E/flutter (12986): #9     SembastStore.txnAdd (package:sembast/src/store_impl.dart:117:11) E/flutter (12986): <asynchronous suspension> E/flutter (12986): #10    StoreRefMixin.add.<anonymous closure> (package:sembast/src/store_ref_impl.dart:75:12) E/flutter (12986): #11 SembastDatabase.inTransaction.<anonymous closure> (package:sembast/src/database_impl.dart:1238:34) E/flutter (12986):
#12     SembastDatabase.transaction.<anonymous closure>.<anonymous closure> (package:sembast/src/database_impl.dart:1090:59) E/flutter (12986): #13     new Future.sync (dart:async/future.dart:224:31) E/flutter (12986): #14     SembastDatabase.transaction.<anonymous closure> (package:sembast/src/database_impl.dart:1090:26) E/flutter (12986): #15     BasicLock.synchronized (package:synchronized/src/basic_lock.dart:32:26) E/flutter (12986):
#16     SembastDatabase.transaction (package:sembast/src/database_impl.dart:1073:38) E/flutter (12986):
#17     SembastDatabase.inTransaction (package:sembast/src/database_impl.dart:1238:7) E/flutter (12986): #18 StoreRefMixin.add (package:sembast/src/store_ref_impl.dart:72:25) E/flutter (12986): #19     ParentDao.insert (package:json_serial_test/data/parent_dao.dart:17:24) E/flutter (12986): <asynchronous suspension> E/flutter (12986): #20    
_MyHomePageState.build.<anonymous closure> (package:json_serial_test/main.dart:120:22) E/flutter (12986): #21    
_InkResponseState._handleTap (package:flutter/src/material/ink_well.dart:706:14) E/flutter (12986):
#22     _InkResponseState.build.<anonymous closure> (package:flutter/src/material/ink_well.dart:789:36) E/flutter (12986):
#23     GestureRecognizer.invokeCallback (package:flutter/src/gestures/recognizer.dart:182:24) E/flutter (12986): #24     TapGestureRecognizer.handleTapUp (package:flutter/src/gestures/tap.dart:486:11) E/flutter (12986): #25  BaseTapGestureRecognizer._checkUp (package:flutter/src/gestures/tap.dart:264:5) E/flutter (12986): #26   BaseTapGestureRecognizer.acceptGesture (package:flutter/src/gestures/tap.dart:236:7) E/flutter (12986): #27   GestureArenaManager.sweep (package:flutter/src/gestures/arena.dart:156:27) E/flutter (12986):
#28     GestureBinding.handleEvent (package:flutter/src/gestures/binding.dart:222:20) E/flutter (12986):
#29     GestureBinding.dispatchEvent (package:flutter/src/gestures/binding.dart:198:22) E/flutter (12986):
#30     GestureBinding._handlePointerEvent (package:flutter/src/gestures/binding.dart:156:7) E/flutter (12986):
#31     GestureBinding._flushPointerEventQueue (package:flutter/src/gestures/binding.dart:102:7) E/flutter (12986):
#32     GestureBinding._handlePointerDataPacket (package:flutter/src/gestures/binding.dart:86:7) E/flutter (12986):
#33     _rootRunUnary (dart:async/zone.dart:1138:13) E/flutter (12986): #34     _CustomZone.runUnary (dart:async/zone.dart:1031:19) E/flutter (12986): #35     _CustomZone.runUnaryGuarded (dart:async/zone.dart:933:7) E/flutter (12986): #36     _invoke1 (dart:ui/hooks.dart:273:10) E/flutter (12986): #37    
_dispatchPointerDataPacket (dart:ui/hooks.dart:182:5) E/flutter (12986):

如果有人可以帮助我展示我遗漏或做错的地方，我将不胜感激。

原版POST ============== 应该 json_serializable 将所有 class 转换为 JSON，还是我遇到的限制？

我决定通过使用 json_serializable 创建处理 NoSQL DB.[=25= 所需的 toJson 和 fromJson 方法来尝试解决我自己造成的一系列问题]

如果我创建一个 class，其中包含一个 List<Ojb> 字段，生成的代码似乎会为 class 的每个字段生成 JSON，但是无法对列表中的对象执行此操作。

简单示例

class Parent {
  final int age;
  final String name;
  List<Child> children;

  Parent({this.age, this.name, this.children});

}

class Child {
  final int age;
  final String name;

  Child({this.age, this.name});
}

当我使用 json_serializable 时，它似乎工作得很好，我得到了上面提到的 classes 的 toJson 和 fromJson 方法。乍一看，一切看起来都很完美。

当我尝试将一个父项（包含子项）插入到我的 NoSQL 数据库中时，插入未能说明不支持该类型（引用子项对象）- 正确的声明，没有问题。

当我通过调试器单步执行此操作时，这就是我所看到的。

Parent转换为地图年龄以其价值显示为关键该名称显示为键及其值

到目前为止，我可以看到一切都是地图[..而且一切看起来都很棒

然后我们进入子对象列表。

这部分未转换为映射，但仍作为子对象列表存在，因此插入失败。

两个 class 都有 jsonSerializable 注释 classes 都在生成预期的代码（部分），classes

只要我不尝试在我的 classes 中使用 List<myObject>，一切都会完美无缺。

人们使用像 json_serializable 这样的包的全部原因是依赖于自动生成的代码，而不必自己构建它。我不想手动更新自动生成的代码来解决这个问题，这就是我没有粘贴代码的原因。如果那是答案，那么我会走另一条路。

我的问题是...是否有一些我遗漏或可能做错的配置允许 class 中的所有项目转换为 map/json，即使 class 的字段不仅仅是简单的 int 和 string 类型。我希望我可以有一个 class ，其中包括基元、对象、对象列表等，并且一切都应该正确生成，或者没有？

Answer 1

经过多次试验和重建，我已经解决了这个问题，现在一切似乎都可以在我的 Sembast 数据库中使用 json_serializable 用于我的模型 classes。可能还有其他因素促成了我的成功，但我认为主要区别在于将以下参数添加到 Parent class.

的 JSONSerializable 注释中

explicitToJson: true

这是代码，如果它能帮助其他人的话。

您可以在此处找到完整的解释 https://flutter.dev/docs/development/data-and-backend/json

@JsonSerializable(explicitToJson: true)
class Parent {
  int id;
  final String name;
  final int age;
  List<Child> children;
  Job job;

  Parent({this.name, this.age, this.children, this.job});

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

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

json_serializable 的复杂模型 - 列表 <objects> 未转换为地图

Complex models with json_serializable - List<objects> not converting to map

serializable

dart

flutter