support custom json converter for generic fields about freezed HOT 13 CLOSED

@freezed
class NewsPost with _$NewsPost {
  factory NewsPost({
    @TimestampConverter() @JsonKey(name: "date") DateTime? date,
  }) = _NewsPost;

  factory NewsPost.fromJson(Map<String, dynamic> json) =>
      _$NewsPostFromJson(json);
}

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:freezed_annotation/freezed_annotation.dart';

class TimestampConverter implements JsonConverter<DateTime, Timestamp> {
  const TimestampConverter();

  @override
  DateTime fromJson(Timestamp timestamp) {
    return timestamp.toDate();
  }

  @override
  Timestamp toJson(DateTime date) => Timestamp.fromDate(date);
}

/// Converts DateTime to Timestamp for serialization of Firestore object
Timestamp dateTimeToJson(DateTime? dateTime) =>
    Timestamp.fromDate(dateTime ?? DateTime(2021));

/// Converts Timestamp to DateTime for serialization of Firestore object
DateTime? dateTimeFromJson(Timestamp? timestamp) =>
    timestamp?.toDate() ?? DateTime(2021);

class NewsPost with _$NewsPost {
  factory NewsPost({
    @JsonKey(name: 'date', fromJson: dateTimeFromJson, toJson: dateTimeToJson)
        DateTime? date,
  }) = _NewsPost;

  factory NewsPost.fromJson(Map<String, dynamic> json) =>
      _$NewsPostFromJson(json);
}

@freezed
class UserDetails with _$UserDetails {
  factory UserDetails({
    required String firstName,
    required String lastName,
    @JsonKey(name: 'date')
    @CustomDateTimeConverter()
        required DateTime dateOfBirth,
    required String email,
    required String street,
    required String city,
    required String state,
  }) = _UserDetails;

  factory UserDetails.blank() => UserDetails(
        firstName: '',
        lastName: '',
        dateOfBirth: DateTime.fromMillisecondsSinceEpoch(0),
        email: '',
        street: '',
        city: '',
        state: '',
      );

  factory UserDetails.fromJson(Map<String, dynamic> json) =>
      _$UserDetailsFromJson(json);
}

class CustomDateTimeConverter implements JsonConverter<DateTime, String> {
  const CustomDateTimeConverter();

  @override
  DateTime fromJson(String json) {
    return DateTime.parse(json);
  }

  @override
  String toJson(DateTime dt) => DateFormat('yyyy-MM-dd').format(dt);
}

...
/// @nodoc
mixin _$UserDetails {
  String get firstName => throw _privateConstructorUsedError;
  String get lastName => throw _privateConstructorUsedError;
  @JsonKey(name: 'date')
  @CustomDateTimeConverter()
  DateTime get dateOfBirth => throw _privateConstructorUsedError;
  String get email => throw _privateConstructorUsedError;
...

void main() {
  test('user details model serialises to expected date format', () async {
    final testUser = UserDetails.blank();

    final expectedJson =
        '{"firstName":"","lastName":"","date":"1970-01-01","email":"","street":"","city":"","state":""}';

    expect(json.encode(testUser.toJson()), expectedJson);
  });
}