在 Flutter Dart 中解析 JSON 时忽略可空引用类的必填字段

Question

我当前正在尝试显示一个引用多个其他类但可以为空的类，因为它并不总是确定哪个引用的类具有值。现在，由于

Dart

积极尝试加载您在模型类中声明的所有必需内容，它想要加载可空类的所有字段，而我真的不想这样做。我可以做什么来限制这种行为？当我必须自己处理那些引用的类时，这还好，但这一次真的很烦人，因为我已经将它们设置为可为空，并且它们仍在尝试加载。

这是我到目前为止的代码：

这是我在问题中提到的模型：

import 'package:json_annotation/json_annotation.dart';

part 'delivery.g.dart';

enum DeliveryStatus {
  @JsonValue(0)ToBeConfirmed,
  @JsonValue(1)Ongoing,
  @JsonValue(2)Received,
  @JsonValue(3)Cancelled,
}

@JsonSerializable(explicitToJson: true)
class Delivery{
  Delivery({
    this.id,
    this.shippingDoc,
    this.shippingDocId,
    this.vhc,
    this.vhcId,
    this.aic,
    this.aicId,
    required this.status,
    required this.receivedOnDatetime,
    this.receivedBy,
    required this.receivedById,
    this.remarks,
    this.isConfirmed,
    this.isCancelled,
    this.confirmedOnDatetime,
    this.cancelledOnDatetime,
  });

  @JsonKey(name: 'id')
  String? id = "";

  @JsonKey(name: 'shipping_doc')
  ShippingDoc? shippingDoc;

  @JsonKey(name: 'shipping_doc_id')
  String? shippingDocId = "";

  @JsonKey(name: 'vhc')
  VhcApplication? vhc;

  @JsonKey(name: 'vhc_id')
  String? vhcId = "";

  @JsonKey(name: 'aic')
  VhcApplication? aic;

  @JsonKey(name: 'aic_id')
  String? aicId = "";

  @JsonKey(name: 'status')
  DeliveryStatus status = DeliveryStatus.ToBeConfirmed;

  @JsonKey(name: 'received_on_datetime')
  String receivedOnDatetime = '';

  @JsonKey(name: 'received_by')
  User? receivedBy;

  @JsonKey(name: 'received_by_id')
  String receivedById = "";

  @JsonKey(name: 'remarks')
  String? remarks = "";

  @JsonKey(name: 'is_confirmed')
  bool? isConfirmed = false;

  @JsonKey(name: 'is_cancelled')
  bool? isCancelled = false;

  @JsonKey(name: 'confirmed_on_datetime')
  String? confirmedOnDatetime = "";

  @JsonKey(name: 'cancelled_on_datetime')
  String? cancelledOnDatetime = "";

  factory Delivery.fromJson(Map<String, dynamic> json) => _$DeliveryFromJson(json);
  Map<String, dynamic> toJson() => _$DeliveryToJson(this);
}

引用的类是ShippingDoc VhcApplication和VhcApplication（我还没有实现aic的真正类）。现在，ShippingDoc 很有价值，因为我拥有了它。另一方面，VhcApplication 是并且应该为 null，并且是导致问题的原因，因为它为 null 但

Dart

仍然想要加载它的字段

Answer 1

您可以更新 JsonKey 注释并使用

includeFromJson: false

和/或

includeToJson: false

像这样：

@JsonKey(includeFromJson: false, includeToJson: false)
  VhcApplication? vhc;

参考： https://pub.dev/documentation/json_annotation/4.9.0/json_annotation/JsonKey-class.html