Json_serializable.dart: how to set default value to nested JSON objects?

Created on 18 Jan 2021 · 6Comments · Source: google/json_serializable.dart

I am trying to figure out how to properly set the default value to nested JSON fields.
I am trying to avoid null values for missing fields in the response json.

I have tried this:

@JsonSerializable(explicitToJson: true)
class LoginResponse {
  @JsonKey(defaultValue: false)
  bool success;
  @JsonKey(defaultValue: new UserDataModel())
  UserDataModel seeker;
  @JsonKey(defaultValue: 0)
  int timestamp;

but the syntax is not correct as the value must be a constant.

I have also tried this:

@JsonSerializable(explicitToJson: true)
class LoginResponse {
  @JsonKey(defaultValue: false)
  bool success;
  @JsonKey(disallowNullValue: true, defaultValue: {"seeker": {"id": "", "name": "", "email": "",}})
  UserDataModel seeker;
  @JsonKey(defaultValue: 0)
  int timestamp;

Generated code:

LoginResponse _$LoginResponseFromJson(Map<String, dynamic> json) { $checkKeys(json, disallowNullValues: const ['seeker']); return LoginResponse( success: json['success'] as bool ?? false, seeker: json['seeker'] == null ? null : UserDataModel.fromJson(json['seeker'] as Map<String, dynamic>) ?? { 'seeker': { 'id': '', 'name': '', 'email': '' } }, timestamp: json['timestamp'] as int ?? 0, ); }

but when the response does not include the field, it is still set to null.
Any help would be appreciated.

Source

PfizerVaccine

👍4

Most helpful comment

This is in demand for us too. We should be able to use an own object as defaultValue, like @JsonKey(defaultValue: PriceData()), so this:

    basePrice: json['basePrice'] == null
        ? null
        : PriceData.fromJson(json['basePrice'] as Map<String, dynamic>),

should be changed into this:

    basePrice: json['basePrice'] == null
        ? PriceData()
        : PriceData.fromJson(json['basePrice'] as Map<String, dynamic>),

Dohmanlechx on 27 Jan 2021

👍3

All 6 comments

Here is out of jail card :

UserDataModel _$UserDataModel(Map<String, dynamic> json) {
  if (json != null) {
    return UserDataModel(
      personId: json['userDataModelId'] as int ?? 0,
    );
  } else {
    return (UserDataModel(
      personId: 0,
   ));
  }
}

pierre-gancel on 19 Jan 2021

This is in demand for us too. We should be able to use an own object as defaultValue, like @JsonKey(defaultValue: PriceData()), so this:

    basePrice: json['basePrice'] == null
        ? null
        : PriceData.fromJson(json['basePrice'] as Map<String, dynamic>),

should be changed into this:

    basePrice: json['basePrice'] == null
        ? PriceData()
        : PriceData.fromJson(json['basePrice'] as Map<String, dynamic>),

Dohmanlechx on 27 Jan 2021

👍3

This gets a bit complicated.

We _could_ add in logic to support the encoded version of a type in defaultsTo (or add another configuration option). Then we'd pass that in as PriceData.fromJson(json['price] as Map<String, dynamic>? ?? const {...}

But that gets super complicated!

I'm going to suggest that folks just create a fromJson converter here. Take in Map<String, dynamic>? and handle returning whatever you like in the null case.

I don't think the added complexity here is worth it!