使用dart-json_serializable将对象字段映射到json平面键(一对多映射)

Question

我有一个dart对象，它包括一个类型为Money的字段，它本身由amount和currency:组成

@JsonSerializable()
class Account {
final String id;
final String type;
final String subtype;
final String origin;
final String name;
final String status;
final String currency;
final Money balance; <== value object
...
}

Money看起来像这样：

class Money {
final int amount;
final String currency;
const Money(this.amount, this.currency);
...
}

以上内容将被映射以供sqflite使用，因此目标JSON必须是一个平面JSON，如：

{
"id": String,
"type": String,
"subtype": String,
"origin": String,
"name": String,
"status": String,
"currency": String,
"balanceAmount": int;      <== value object
"balanceCurrency": String; <== value object
}

我知道我可以在解码之前使用JsonKey.readValue从整个JSON对象中提取一个复合对象。

但是我怎么能做相反的事情呢？从Money实例中获取两个值，并将它们映射到balanceAmount和balanceCurrency

我在json_serializableapi文档、GitHub问题或StackOverflow上进行的搜索似乎没有特别回应这一点：如何将一个字段映射到两个(或多个(目标键？

Answer 1

如果生成的代码在"balance"中使用完整的json，这个解决方案会更好像这样：

Money.fromJson(json(

但我不知道该怎么做：(

import 'package:project/test/money.dart';
import 'package:json_annotation/json_annotation.dart';
part 'account.g.dart';
@JsonSerializable()
class Account {
final String id;
final String type;
final String subtype;
final String origin;
final String name;
final String status;
final String currency;
@JsonKey(fromJson: _dataFromJson)
final Money balance; // <== value object
Account({
required this.id,
required this.type,
required this.subtype,
required this.origin,
required this.name,
required this.status,
required this.currency,
required this.balance,
});
static Money _dataFromJson(Object json) {
if (json is Map<String, dynamic>) {
return Money(amount: json["balanceAmount"], currency: json["balanceCurrency"]);
}
throw ArgumentError.value(
json,
'json',
'Cannot convert the provided data.',
);
// return Money(amount: 0, currency:"");
}
factory Account.fromJson(Map<String, dynamic> json) => Account(
id: json['id'] as String,
type: json['type'] as String,
subtype: json['subtype'] as String,
origin: json['origin'] as String,
name: json['name'] as String,
status: json['status'] as String,
currency: json['currency'] as String,
balance: Money.fromJson(json),
);
Map<String, dynamic> toJson() => _$AccountToJson(this);
}
// {
//   "id": String,
//   "type": String,
//   "subtype": String,
//   "origin": String,
//   "name": String,
//   "status": String,
//   "currency": String,
//   "balanceAmount": int;      <== value object
//   "balanceCurrency": String; <== value object
// }