Converting Firebase Realtime database json response from _InternalLinkedHashMap<Object?, Object?> to Map<String,dynamic>

user_6655405 0
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I have a database in my Firebase Realtime database with children that look like this: enter image description here

Here's the JSON that I receive in my Flutter app from my firebase call:

{
  "gameAnalytics" : {
    "log" : {
      "20210926073039AbMc4uSXywqpK9OcusSV" : {
        "cityID" : "newYork",
        "countryCode" : "USA",
        "gameID" : "20210927065000Upper90IndnewYofootbiGZYy",
        "gamePaymentMethod" : "payAtPitch",
        "players" : {
          "umZ5ezrtI6a3UoCDWFDc3hInoNA2" : {
            "pnam" : "Mario Rest",
            "url" : "https://i.ibb.co/blahblah.jpg"
          }
        },
        "sportID" : "football",
        "status" : {
          "202109261130395laHd8h77R" : "completing, send back",
          "20210926113039BcUQ8RdbHs" : "payAtPitch",
          "20210926113039Ck9JsD1uf1" : "playersAdded"
        },
        "timeAndDateString" : "20210926073039",
        "totalCost" : 999,
        "type" : "ADD",
        "userWhoAddedID" : "umZ5ezrtI6a3UoCDWFDc3hInoNA2",
        "wantsToBeOrganizer" : true
      },
      "202109261146540focIuCQRi3wNfSluvkl" : {
        "cityID" : "newYork",
        "countryCode" : "USA",
        "gameID" : "20210927065000Upper90IndnewYofootbiGZYy",
        "gamePaymentMethod" : "payByBalance",
        "players" : {
          "hOBQJtqCCNgGBVrAv2MqeaFJmdu1" : {
            "pnam" : "Seong Kang",
            "url" : "messi"
          }
        },
        "promoCodeData" : "U90qaL",
        "sportID" : "football",
        "status" : {
          "2021092615465414NXsxwW51" : "playersAdded",
          "20210926154654A60TLCmS2t" : "paidByBalance",
          "20210926154654VtYR1t4bMZ" : "completing, send back"
        },
        "timeAndDateString" : "20210926114654",
        "totalCost" : 0,
        "type" : "ADD",
        "userWhoAddedID" : "hOBQJtqCCNgGBVrAv2MqeaFJmdu1",
        "wantsToBeOrganizer" : false
      },
      "20210926204533DjF3lMCMDpvwHfsh6lQJ" : {
        "amountToRefund" : 0,
        "promoCodes" : {
          "hOBQJtqCCNgGBVrAv2MqeaFJmdu1" : "U90qaL"
        },
        "status" : {
          "20210927004533ZWGNEMX27V" : "REFUNDING: 0  null  hOBQJtqCCNgGBVrAv2MqeaFJmdu1"
        },
        "type" : "CANCEL",
        "userWhoAddedID" : "hOBQJtqCCNgGBVrAv2MqeaFJmdu1"
      }
    },
    "pitchCost" : 3500,
    "playerNumbers" : {
      "hoursBefore12" : 2,
      "hoursBefore24" : 1,
      "hoursBefore3" : 2,
      "hoursBefore36" : 1,
      "hoursBefore48" : 1,
      "hoursBefore6" : 2,
      "hoursBefore72" : 1,
      "hoursBefore96" : 1
    },
    "timings" : {
      "added" : {
        "20210917004938" : "organiserID12345",
        "20210926113040" : "umZ5ezrtI6a3UoCDWFDc3hInoNA2",
        "20210926154656" : "hOBQJtqCCNgGBVrAv2MqeaFJmdu1"
      },
      "cancelled" : {
        "20210917004939" : "playersUnCancelled",
        "20210927004522" : "playersCancelled"
      },
      "removed" : {
        "20210926113042" : "organiserID12345"
      }
    }
  },
  "gameData" : {
    "addFakePlayers" : false,
    "can" : true,
    "canAddPromoCode" : true,
    "canDes" : {
      "en" : "somedesc"
    },
    "canMes" : "blahblah.",
    "cost" : 999,
    "cur" : 2,
    "currency" : "usd",
    "dat" : "20210927065000",
    "descriptions" : {
      "en" : "blahblah"
    },
    "dur" : "60 minutes",
    "expOrg" : "",
    "gameTypes" : {
      "en" : "blahblah"
    },
    "hostConfirmed" : false,
    "hostInfo" : {
      "hostDescription" : "blahblah",
      "hostNickname" : "Mario R",
      "hostPhoto" : "https://i.ibb.co/blahblah.jpg",
      "isSuperHost" : false
    },
    "lid" : "Upper90IndoorQueensabcde739219515176663407563157034467ap0mr",
    "max" : 15,
    "mes" : "blahblah",
    "mes1" : "my disappointment",
    "mes2" : "is immessurable",
    "mes3" : "and my day",
    "payAtPitchMessage" : {
      "en" : "is ruined"
    },
    "paymentType" : "justOnline",
    "paymentsAllowed" : [ "card" ],
    "pla1" : {
      "hOBQJtqCCNgGBVrAv2MqeaFJmdu1" : {
        "pnam" : "blahblah",
        "url" : "messi"
      }
    },
    "pla2" : {
      "umZ5ezrtI6a3UoCDWFDc3hInoNA2" : {
        "organizer" : true,
        "pnam" : "Mario Rest",
        "url" : "https://i.ibb.co/blahblah.jpg"
      }
    },
    "pub" : false,
    "removalAllowed" : true,
    "showHostConfirmButton" : false,
    "spotEn" : true,
    "surl" : "https://someurl",
    "title" : {
      "en" : "ok"
    }
  },
  "mess" : {
    "-MjlDj5szZxKaDs0p3CN" : {
      "mes" : "ok",
      "tim" : "20210916204938",
      "unm" : "blahblah",
      "usi" : "XwyPhbjzeKNYVczPdCPFTG0DZbj1"
    },
    "-MjlDj6bnMvKUO76EjLE" : {
      "mes" : "ok",
      "tim" : "20210916204938",
      "unm" : "blahblah",
      "usi" : "XwyPhbjzeKNYVczPdCPFTG0DZbj1"
    },
    "-MjlDj7SeqRV0KzRzFFX" : {
      "mes" : "ok",
      "tim" : "20210916204939",
      "unm" : "bllblb",
      "usi" : "XwyPhbjzeKNYVczPdCPFTG0DZbj1"
    },
    "-MjlDj8C-p406IK8I-cb" : {
      "mes" : "msg",
      "tim" : "20210916204940",
      "unm" : "msg",
      "usi" : "XwyPhbjzeKNYVczPdCPFTG0DZbj1"
    }
  },
  "payment" : {
    "playerPaymentStatus" : {
      "hOBQJtqCCNgGBVrAv2MqeaFJmdu1" : {
        "date" : "20210927004533",
        "refundedAmount" : 0,
        "stripePaymentNotConfirmed" : true,
        "type" : "notPaidForGame",
        "userWhoAddedID" : "hOBQJtqCCNgGBVrAv2MqeaFJmdu1"
      }
    }
  },
  "userReview" : {
    "showReview" : true
  }
}

I'm trying to create a Map<String, dynamic> from this response by using Map<String,dynamic>.from() as seen below:

class PickUpGameItem extends StatefulWidget {
  final String gameId;

  const PickUpGameItem(this.gameId, [Key? key]) : super(key: key);

  @override
  _PickUpGameItemState createState() => _PickUpGameItemState();
}

class _PickUpGameItemState extends State<PickUpGameItem> {
  late StreamSubscription _pickUpGameDetailsStreamSub;
  PickUpGameDetails? gameDetails;

  @override
  void initState() {
    super.initState();
    _setListeners();
  }

  @override
  void deactivate() {
    _pickUpGameDetailsStreamSub.cancel();
    super.deactivate();
  }

  void _setListeners() {
    _pickUpGameDetailsStreamSub = FirebaseDatabase()
        .reference()
        .child(
            '.../gamesDetailed/${widget.gameId}/')
        .onValue
        .listen((event) {
      final detailsJson = Map<String, dynamic>.from(event.snapshot.value);
      setState(() {
        gameDetails = PickUpGameDetails.fromJson(detailsJson);
        print(gameDetails.toString());
      });
    });
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: const EdgeInsets.symmetric(horizontal: 20, vertical: 20),
      child: Row(
        children: [
          ClipRRect(
            borderRadius: BorderRadius.circular(8.0),
            child: const Image(
              fit: BoxFit.fill,
              width: 80.0,
              height: 80.0,
              image: AssetImage('assets/images/temp_city_img.jpg'),
            ),
          ),
          const SizedBox(
            width: 10,
          ),
          Expanded(
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: const [
                Text(
                  'Lorem ipsum dolor sit amet this is a test ......................................',
                  style: TextStyle(
                      color: Colors.black,
                      fontWeight: FontWeight.bold,
                      fontSize: 16),
                  maxLines: 1,
                  overflow: TextOverflow.ellipsis,
                ),
                SizedBox(
                  height: 10,
                ),
                Text(
                  'Lorem ipsum dolor sit amet this is a test ......................................',
                  style: TextStyle(
                      color: Colors.grey,
                      fontWeight: FontWeight.normal,
                      fontSize: 14),
                  maxLines: 1,
                  overflow: TextOverflow.ellipsis,
                ),
              ],
            ),
          ),
          const SizedBox(
            width: 10,
          ),
          Flexible(
            flex: 0,
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: [
                const Text(
                  'Football',
                  style: TextStyle(
                      color: Colors.black,
                      fontWeight: FontWeight.bold,
                      fontSize: 16),
                ),
                const SizedBox(
                  height: 10,
                ),
                Row(
                  children: const [
                    Text(
                      '14/16',
                      style: TextStyle(
                          color: Colors.grey,
                          fontWeight: FontWeight.normal,
                          fontSize: 14),
                    ),
                    SizedBox(
                      width: 5,
                    ),
                    Icon(Icons.ac_unit)
                  ],
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}

When I run the app, I get an error saying that the internal linked hash map isn't a subtype of map and that the error occurs when calling GameAnalytics.fromJson(). I've seen multiple similar posts but their error mentioned an _InternalLinkedHashMap<String?, dynamic> map. Why Is this linked hash map in my response using Object? for both keys and values?

[ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: type '_InternalLinkedHashMap<Object?, Object?>' is not a subtype of type 'Map<String, dynamic>'

Here are my dart model classes:

PickUpGameDetails.dart:

class PickUpGameDetails {
  GameAnalytics? gameAnalytics;
  GameData? gameData;
  UserReview? userReview;

  PickUpGameDetails(
      {required this.gameAnalytics,
      required this.gameData,
      required this.userReview});

  PickUpGameDetails.fromJson(Map<String, dynamic> json) {
    gameAnalytics = json['gameAnalytics'] != null
        ? GameAnalytics.fromJson(json['gameAnalytics'])
        : null;
    gameData =
        json['gameData'] != null ? GameData.fromJson(json['gameData']) : null;
    userReview = json['userReview'] != null
        ? UserReview.fromJson(json['userReview'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (gameAnalytics != null) {
      data['gameAnalytics'] = gameAnalytics!.toJson();
    }
    if (gameData != null) {
      data['gameData'] = gameData!.toJson();
    }
    if (userReview != null) {
      data['userReview'] = userReview!.toJson();
    }
    return data;
  }
}

GameAnalytics.dart:

class GameAnalytics {
  late int pitchCost;
  PlayerNumbers? playerNumbers;
  Timings? timings;

  GameAnalytics(
      {required this.pitchCost,
      required this.playerNumbers,
      required this.timings});

  GameAnalytics.fromJson(Map<String, dynamic> json) {
    pitchCost = json['pitchCost'];
    playerNumbers = json['playerNumbers'] != null
        ? PlayerNumbers.fromJson(json['playerNumbers'])
        : null;
    timings =
        json['timings'] != null ? Timings.fromJson(json['timings']) : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['pitchCost'] = pitchCost;
    if (playerNumbers != null) {
      data['playerNumbers'] = playerNumbers!.toJson();
    }
    if (timings != null) {
      data['timings'] = timings!.toJson();
    }
    return data;
  }
}

PlayerNumbers.dart:

class PlayerNumbers {
  late int hoursBefore12;
  late int hoursBefore24;
  late int hoursBefore3;
  late int hoursBefore36;
  late int hoursBefore48;
  late int hoursBefore6;
  late int hoursBefore72;
  late int hoursBefore96;

  PlayerNumbers(
      {required this.hoursBefore12,
      required this.hoursBefore24,
      required this.hoursBefore3,
      required this.hoursBefore36,
      required this.hoursBefore48,
      required this.hoursBefore6,
      required this.hoursBefore72,
      required this.hoursBefore96});

  PlayerNumbers.fromJson(Map<String, dynamic> json) {
    hoursBefore12 = json['hoursBefore12'];
    hoursBefore24 = json['hoursBefore24'];
    hoursBefore3 = json['hoursBefore3'];
    hoursBefore36 = json['hoursBefore36'];
    hoursBefore48 = json['hoursBefore48'];
    hoursBefore6 = json['hoursBefore6'];
    hoursBefore72 = json['hoursBefore72'];
    hoursBefore96 = json['hoursBefore96'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['hoursBefore12'] = hoursBefore12;
    data['hoursBefore24'] = hoursBefore24;
    data['hoursBefore3'] = hoursBefore3;
    data['hoursBefore36'] = hoursBefore36;
    data['hoursBefore48'] = hoursBefore48;
    data['hoursBefore6'] = hoursBefore6;
    data['hoursBefore72'] = hoursBefore72;
    data['hoursBefore96'] = hoursBefore96;
    return data;
  }
}

Timings.dart:

class Timings {
  Map<String, dynamic>? added;
  Map<String, dynamic>? cancelled;
  Map<String, dynamic>? removed;

  Timings(
      {required this.added, required this.cancelled, required this.removed});

  Timings.fromJson(Map<String, dynamic> json) {
    added = json['added'];
    cancelled = json['cancelled'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    if (added != null) {
      data['added'] = added;
    }
    if (cancelled != null) {
      data['cancelled'] = cancelled;
    }
    if (removed != null) {
      data['removed'] = removed;
    }
    return data;
  }
}

UserReview.dart:

class UserReview {
  bool? showReview;

  UserReview({required this.showReview});

  UserReview.fromJson(Map<String, dynamic> json) {
    showReview = json['showReview'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['showReview'] = showReview;
    return data;
  }
}

GameData.dart:

class GameData {
  late bool addFakePlayers;
  late bool hasBeenCancelled;
  late bool canAddPromoCode;
  late String cancellationDescription;
  late String cancellationMsg;
  late int cost;
  late int cur;
  late String currency;
  late String dateTime;
  late String description;
  late String durationMsg;
  late String expOrg;
  late String gameTypeMsg;
  late bool hostConfirmed;
  late String lid;
  late int maxPlayers;
  late List<String> messages;
  late String payAtPitchMessage;
  late String paymentType;
  late List<String> paymentsAllowed;
  Team? team1;
  Team? team2;
  late bool pub;
  late bool removalAllowed;
  late bool showHostConfirmButton;
  late bool spotEn;
  late String surl;
  late String title;

  GameData(
      {required this.addFakePlayers,
      required this.hasBeenCancelled,
      required this.canAddPromoCode,
      required this.cancellationDescription,
      required this.cancellationMsg,
      required this.cost,
      required this.cur,
      required this.currency,
      required this.dateTime,
      required this.description,
      required this.durationMsg,
      required this.expOrg,
      required this.gameTypeMsg,
      required this.hostConfirmed,
      required this.lid,
      required this.maxPlayers,
      required this.messages,
      required this.payAtPitchMessage,
      required this.paymentType,
      required this.paymentsAllowed,
      required this.team1,
      required this.team2,
      required this.pub,
      required this.removalAllowed,
      required this.showHostConfirmButton,
      required this.spotEn,
      required this.surl,
      required this.title});

  GameData.fromJson(Map<String, dynamic> json) {
    addFakePlayers = json['addFakePlayers'];
    hasBeenCancelled = json['can'];
    canAddPromoCode = json['canAddPromoCode'];
    cancellationDescription = json['canDes']['en'];
    cancellationMsg = json['canMes'];
    cost = json['cost'];
    cur = json['cur'];
    currency = json['currency'];
    dateTime = json['dat'];
    description = json['descriptions']['en'];
    durationMsg = json['dur'];
    expOrg = json['expOrg'];
    gameTypeMsg = json['gameTypes']['en'];
    hostConfirmed = json['hostConfirmed'];
    lid = json['lid'];
    maxPlayers = json['max'];
    messages.add(json['mes']);
    messages.add(json['mes1']);
    messages.add(json['mes2']);
    messages.add(json['mes3']);
    payAtPitchMessage = json['payAtPitchMessage']['en'];
    paymentType = json['paymentType'];
    paymentsAllowed = json['paymentsAllowed'].cast<String>();
    team1 = json['pla1'] != null ? Team.fromJson(json['pla1']) : null;
    team2 = json['pla2'] != null ? Team.fromJson(json['pla2']) : null;
    pub = json['pub'];
    removalAllowed = json['removalAllowed'];
    showHostConfirmButton = json['showHostConfirmButton'];
    spotEn = json['spotEn'];
    surl = json['surl'];
    title = json['title']['en'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = <String, dynamic>{};
    data['addFakePlayers'] = addFakePlayers;
    data['can'] = hasBeenCancelled;
    data['canAddPromoCode'] = canAddPromoCode;
    data['canDes'] = cancellationDescription;
    data['canMes'] = cancellationMsg;
    data['cost'] = cost;
    data['cur'] = cur;
    data['currency'] = currency;
    data['dat'] = dateTime;
    data['descriptions'] = description;
    data['dur'] = durationMsg;
    data['expOrg'] = expOrg;
    data['gameTypes'] = gameTypeMsg;
    data['hostConfirmed'] = hostConfirmed;
    data['lid'] = lid;
    data['max'] = maxPlayers;
    data['mes'] = messages.elementAt(0);
    data['mes1'] = messages.elementAt(1);
    data['mes2'] = messages.elementAt(2);
    data['mes3'] = messages.elementAt(3);
    data['payAtPitchMessage'] = payAtPitchMessage;
    data['paymentType'] = paymentType;
    data['paymentsAllowed'] = paymentsAllowed;
    data['pla1'] = team1?.toJson();
    data['pla2'] = team2?.toJson();
    data['pub'] = pub;
    data['removalAllowed'] = removalAllowed;
    data['showHostConfirmButton'] = showHostConfirmButton;
    data['spotEn'] = spotEn;
    data['surl'] = surl;
    data['title'] = title;
    return data;
  }
}

Team.dart:

class Team {
  Map<String, Player> players;

  Team({required this.players});

  factory Team.fromJson(Map<String, dynamic> json) {
    Map<String, Player> _players = {};
    for (String key in json.keys) {
      _players[key] = Player.fromJson(json[key]);
    }
    return Team(players: _players);
  }

  Map<String, dynamic> toJson() {
    Map<String, dynamic> json = <String, dynamic>{};
    for (String key in players.keys) {
      json[key] = players[key];
    }
    return json;
  }
}

Player.dart:

class Player {
  String name;
  String url;

  Player({required this.name, required this.url});

  factory Player.fromJson(Map<String, dynamic> json) {
    return Player(name: json['pname'], url: json['url']);
  }

  Map<String, dynamic> toJson() {
    final json = <String, dynamic>{};
    json['pname'] = name;
    json['url'] = url;
    return json;
  }
}
firebase-realtime-database firebase dart flutter json
4 Answers

After searching through multiple Stack posts and GitHub issues on Flutter's repository, I came across this magical line which for some odd reason is the only way to get things to work as of right now. The people that proposed this on flutter's repository also mentioned how weird it is but I'm guessing that Firebase's response is not in a valid JSON format (?). For now, if you want something that works, this is probably it:

jsonDecode(jsonEncode(event.snapshot.value)));

Do note that this is probably bad for performance.

user_66554050

I was able to solve it after investigating how the json value returned by Firebase Real-Time Database actually appears in Flutter.

This unhandled type casting error arises because the RTDB does not return a json object that jsonDecode() can parse. jsonDecode can parse the following json string: -

final source = '{"lastUpdatedID": "R7FIlRodwblI4w", "lastUpdateOn": "1647094887285"}';

But RTDB returns the following json string: -

final source = '{lastUpdatedID: R7FIlRodwblI4w, lastUpdateOn: 1647094887285}';

Notice that the double-quotes are missing. This is why jsonDecode throws an error. So, first we need to add the double-quotes.

final jsonString = origin
      .replaceAll(RegExp(r'\s+'), '')   // To remove all white spaces
      .replaceAll(RegExp(r':'), '":"')  // To add double-quotes on both sides of colon
      .replaceAll(RegExp(r','), '","')  // To add double-quotes on both sides of comma
      .replaceAll(RegExp(r'{'), '{"')   // To add double-quotes after every open curly bracket
      .replaceAll(RegExp(r'}'), '"}');  // To add double-quotes before every closing curly bracket

Now we decode the string: -

final decoded = jsonDecode(jsonString);

We also create a Data Model Class: -

class Model {
  const Model({required this.lastUpdatedID, required this.lastUpdateOn});

  /// This factory constructor parses the [lastUpdateOn] as int (if possible)
  factory Model.fromJson(Map<String, dynamic> json) => Model(
        lastUpdatedID: json['lastUpdatedID'] as String,
        lastUpdateOn: int.tryParse(json['lastUpdateOn']) ?? 0,
      );

  Map<String, dynamic> toJson() => {
        'lastUpdatedID': lastUpdatedID,
        'lastUpdateOn': lastUpdateOn,
      };

  final String lastUpdatedID;
  final int lastUpdateOn;

  @override
  String toString() =>
      'Model(lastUpdatedID: $lastUpdatedID, lastUpdateOn: $lastUpdateOn)';
}

Finally, use the fromJson factory constructor to create a model instance: -

final model = Model.fromJson(value);

Here's the complete code: -

import 'dart:convert';

void main() {
  final origin = '{lastUpdatedID: R7FIlRodwblI4w, lastUpdateOn: 1647094887285}';

  final jsonString = origin
      .replaceAll(RegExp(r'\s+'), '')
      .replaceAll(RegExp(r':'), '":"')
      .replaceAll(RegExp(r','), '","')
      .replaceAll(RegExp(r'{'), '{"')
      .replaceAll(RegExp(r'}'), '"}');
  print(jsonString);

  final value = jsonDecode(jsonString);
  print('value.runtimeType : ' + value.runtimeType.toString());
  print('value : ' + value.toString());

  final model = Model.fromJson(value);
  print('model : $model');
}

class Model {
  const Model({required this.lastUpdatedID, required this.lastUpdateOn});

  factory Model.fromJson(Map<String, dynamic> json) => Model(
        lastUpdatedID: json['lastUpdatedID'] as String,
        lastUpdateOn: int.tryParse(json['lastUpdateOn']) ?? 0,
      );

  Map<String, dynamic> toJson() => {
        'lastUpdatedID': lastUpdatedID,
        'lastUpdateOn': lastUpdateOn,
      };

  final String lastUpdatedID;
  final int lastUpdateOn;

  @override
  String toString() =>
      'Model(lastUpdatedID: $lastUpdatedID, lastUpdateOn: $lastUpdateOn)';
}
user_184487600

I see the problem is within your fromJson method: enter image description here

When creating named constructors, you have 2 possible syntaxes to it:

1. Quick define some params with initializers, without access to this

In this situation, imagine you have a subclass called PickUpGameDetails.noReview where you'd create a fixed userReview object. In this case, you wouldn't process any extra params, only simplify the constructor using initialiser for some params. For this to work, you would add the initialiser before the {, using the :, being something like this (in this case you wouldn't even need to create the context with { }, unless you want to do extra operations besides the initialisers):

PickUpGameDetails.noReview({ 
  required this.gameAnalytics, 
  required this.gameData
}): userReview = {}

2. Use different params and translate to your object constructor

Here we're interested in not only creating some variations from the standard object, but also defining some conversion of inputs to class params.

So you process this after the {, since we'll be able to do more detailed calculations based on the params. Your biggest mistake on this part, is that you're not setting up the class params after processing the json, meaning your object is not being initialised correctly, because you only created some local variables to your constructor. But since this is accessible and waiting to receive the params, the quick fix for your code would be to assign the calculated values to the class params using this:

PickUpGameDetails.mock(Map<String, dynamic> json) {
  this.gameAnalytics = json['gameAnalytics'] != null
      ? GameAnalytics.fromJson(json['gameAnalytics'])
      : null;
  this.gameData =
      json['gameData'] != null ? GameData.fromJson(json['gameData']) : null;
  this.userReview = json['userReview'] != null
      ? UserReview.fromJson(json['userReview'])
      : null;
}

3. Extra: factory

There one other option, that's common when using named constructors that might return different objects, that's the usage of Dart's factory, so your factory is expected to return a new constructed object, which could provide you with flexibility to even change the type / subtype of object being returned based on some extra params. First, for your implementation, it would be something like

factory PickUpGameDetails.fromJson(Map<String, dynamic> json) {
  gameAnalytics = json['gameAnalytics'] != null
      ? GameAnalytics.fromJson(json['gameAnalytics'])
      : null;
  gameData =
      json['gameData'] != null ? GameData.fromJson(json['gameData']) : null;
  userReview = json['userReview'] != null
      ? UserReview.fromJson(json['userReview'])
      : null;

  return PickUpGameDetails(
      gameAnalytics: gameAnalytics, 
      gameData: gameData, 
      userReview: userReview,
    )
}

But the real power of factory would come in case you have a different gameType and want to treat in different classes, so imagining we have a base class Game you could do something like this:

factory Game.fromJson(Map<String, dynamic> json) {
  String gameType = json['gameType']
  if (gameType == 'football') {
    return FootballGame.fromJson(json)
  }
  
  return OtherSportsGame.fromJson(json)
}

This way you set this base class as the responsible to define which class / subclass to initialise.

user_106420350

I found this.

Map<String, dynamic> map = Map<String, dynamic>.from(snap.snapshot.value as Map<dynamic, dynamic>);
user_113840360
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