json - How to handle complex API data response in Flutter GetX using observable method

Question

I am a newbie in the world of flutter and GetX package and I am trying to create a simple app using Laravel as my API service and I am sending the response from the API in JSON format and I am using Laravel resource API so it is sending some extra meta data inside the response and I have already created service model and controller in my flutter app but when I am initializing an observable variable in controller it is throwing a lot error i tried all the methods but it is working fine when i am sending only data list from the API as I have to define List<Model>.obs in controller but the problem is happening when i am sending the proper response from API as required.

Here is my JSON response data from the API

{
    "data": [
        {
            "id": 1,
            "description": "Purchased mouse",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 2,
            "description": "Purchased mouse sa",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 3,
            "description": "Purchased mouse",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 4,
            "description": "Purchased mouse sa",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 5,
            "description": "Purchased mouse",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 6,
            "description": "Purchased mouse sa",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 7,
            "description": "Purchased mouse",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 8,
            "description": "Purchased mouse sa",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 9,
            "description": "Purchased mouse",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 10,
            "description": "Purchased mouse sa",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 11,
            "description": "Purchased mouse",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 12,
            "description": "Purchased mouse sa",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 13,
            "description": "Purchased mouse",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 14,
            "description": "Purchased mouse sa",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        },
        {
            "id": 15,
            "description": "Purchased mouse",
            "amount": "1200",
            "type": "expense",
            "user_id": 1,
            "created_at": null,
            "updated_at": null
        }
    ],
    "links": {
        "first": "http://localhost:8000/api/transactions?page=1",
        "last": "http://localhost:8000/api/transactions?page=2",
        "prev": null,
        "next": "http://localhost:8000/api/transactions?page=2"
    },
    "meta": {
        "current_page": 1,
        "from": 1,
        "last_page": 2,
        "links": [
            {
                "url": null,
                "label": "« Previous",
                "active": false
            },
            {
                "url": "http://localhost:8000/api/transactions?page=1",
                "label": 1,
                "active": true
            },
            {
                "url": "http://localhost:8000/api/transactions?page=2",
                "label": 2,
                "active": false
            },
            {
                "url": "http://localhost:8000/api/transactions?page=2",
                "label": "Next »",
                "active": false
            }
        ],
        "path": "http://localhost:8000/api/transactions",
        "per_page": 15,
        "to": 15,
        "total": 16
    }
}

And here is my service class

import 'dart:convert';

import 'package:http/http.dart' as http;
import 'package:m_budget/models/transaction.dart';

class TransactionService {
  static var client = http.Client();

  static Future<Transaction> fetchTransactions() async {
    var res = await client.get("http://10.0.2.2:8000/api/transactions");
    if (res.statusCode == 200) {
      return transactionFromJson(res.body);
    } else {
      return null;
    }
  }
}

And this is my controller

The main problem is while declaring the observable variable check line no 6 in controller

This one var transactions = Transaction().obs;

import 'package:get/get.dart';
import 'package:m_budget/models/transaction.dart';
import 'package:m_budget/services/transaction_service.dart';

class TransactionController extends GetxController {
  var isLoading = true.obs;

  var transactions = Transaction().obs;

  @override
  void onInit() {
    fetchTransactions();
    super.onInit();
  }

  void fetchTransactions() async {
    isLoading(true);
    try {
      var txns = await TransactionService.fetchTransactions();
      if (txns != null) {
        isLoading(false);
        transactions(txns);
      }
    } catch (e) {} finally {
      isLoading(false);
    }
  }
}

And model code is this

// To parse this JSON data, do
//
//     final transaction = transactionFromJson(jsonString);

import 'dart:convert';

Transaction transactionFromJson(String str) =>
    Transaction.fromJson(json.decode(str));

String transactionToJson(Transaction data) => json.encode(data.toJson());

class Transaction {
  Transaction({
    this.data,
    this.links,
    this.meta,
  });

  List<Datum> data;
  Links links;
  Meta meta;

  factory Transaction.fromJson(Map<String, dynamic> json) => Transaction(
        data: List<Datum>.from(json["data"].map((x) => Datum.fromJson(x))),
        links: Links.fromJson(json["links"]),
        meta: Meta.fromJson(json["meta"]),
      );

  Map<String, dynamic> toJson() => {
        "data": List<dynamic>.from(data.map((x) => x.toJson())),
        "links": links.toJson(),
        "meta": meta.toJson(),
      };
}

class Datum {
  Datum({
    this.id,
    this.description,
    this.amount,
    this.type,
    this.userId,
    this.createdAt,
    this.updatedAt,
  });

  int id;
  String description;
  String amount;
  String type;
  int userId;
  dynamic createdAt;
  dynamic updatedAt;

  factory Datum.fromJson(Map<String, dynamic> json) => Datum(
        id: json["id"],
        description: json["description"],
        amount: json["amount"],
        type: json["type"],
        userId: json["user_id"],
        createdAt: json["created_at"],
        updatedAt: json["updated_at"],
      );

  Map<String, dynamic> toJson() => {
        "id": id,
        "description": description,
        "amount": amount,
        "type": type,
        "user_id": userId,
        "created_at": createdAt,
        "updated_at": updatedAt,
      };
}

class Links {
  Links({
    this.first,
    this.last,
    this.prev,
    this.next,
  });

  String first;
  String last;
  dynamic prev;
  String next;

  factory Links.fromJson(Map<String, dynamic> json) => Links(
        first: json["first"],
        last: json["last"],
        prev: json["prev"],
        next: json["next"],
      );

  Map<String, dynamic> toJson() => {
        "first": first,
        "last": last,
        "prev": prev,
        "next": next,
      };
}

class Meta {
  Meta({
    this.currentPage,
    this.from,
    this.lastPage,
    this.links,
    this.p

Answer 1

item_model.dart

class ItemModel {
  int id;
  String description;
  String amount;
  String type;
  int userId;
  DateTime createdAt;
  DateTime updatedAt;

  ItemModel.fromJson(Map<String, dynamic> data) {
    id = data['id'];
    description = data['description'];
    amount = data['amount'];
    type = data['type'];
    userId = data['userId'];
    if (data['created_at'] != null) createdAt = DateTime.parse(data['created_at']);
    if (data['updated_at'] != null) updatedAt = DateTime.parse(data['updated_at']);
  }
}

page_links_model.dart

class PageLinksModel {
  String first, last, prev, next;

  PageLinksModel.fromJson(Map<String, dynamic> data) {
    first = data['first'];
    last = data['last'];
    prev = data['prev'];
    next = data['next'];
  }
}

pages_status_model.dart

class PagesStatusModel {
  int currentPage, from, lastPage;
  var links = List<PageInfoModel>();
  String path;
  int perPage, to, total;

  PagesStatusModel.fromJson(Map<String, dynamic> data) {
    currentPage = data['current_page'];
    from = data['from'];
    lastPage = data['last_page'];
    (data['links'] as List).forEach((e) => links.add(PageInfoModel.fromJson(e)));
    path = data['path'];
    perPage = data['per_page'];
    to = data['to'];
    total = data['total'];
  }
}

class PageInfoModel {
  String url; 
  dynamic label;
  bool active;

  PageInfoModel.fromJson(Map<String, dynamic> data) {
    url = data['url'];
    label = data['label'];
    active = data['active'];
  }
}

transaction_model.dart

import 'package:getx_api/models/pages_status_model.dart';

class TransactionModel {
  var data = List<ItemModel>();
  PageLinksModel links;
  PagesStatusModel meta;

  TransactionModel.fromJson(Map<String, dynamic> source) {
    (source['data'] as List).forEach((e) => data.add(ItemModel.fromJson(e)));
    links = PageLinksModel.fromJson(source['links']);
    meta = PagesStatusModel.fromJson(source['meta']);
  }
}

net_service.dart

import 'dart:convert';

import 'package:getx_api/src/shared/transactions_data.dart';
import 'package:http/http.dart' as http;

class NetService {
  static Future fetchJsonData(String url) {
    return
      http.get(url)
        .then((response) => response?.statusCode == 200 ? jsonDecode(response.body) : null)
        .catchError((err) => print(err));
  }

  static Future fetchLocalJsonData() async {
    await Future.delayed(Duration(seconds: 3));

    return jsonDecode(transactionData) as Map<String, dynamic>;
  }
}

transaction_controller.dart

import 'package:get/get.dart';
import 'package:getx_api/models/transaction_model.dart';
import 'package:getx_api/services/net_service.dart';


const _serverUrl = 'http://10.0.2.2:8000/api/transactions';

class TransactionController extends GetxController {
  var _trx;
  var _dataAvailable = false.obs;

  @override
  void onInit() {
    super.onInit();
    fetchTransactions();
  }

  bool get dataAvailable => _dataAvailable.value;
  TransactionModel get trx => _trx;

  Future<void> fetchTransactions() {
    // return NetService.fetchJsonData(_serverUrl)
    return NetService.fetchLocalJsonData()
      .then((response) {
        if (response != null) _trx = TransactionModel.fromJson(response);
      })
      .catchError((err) => print('Error!!!!! : $err'))
      .whenComplete(() => _dataAvailable.value = _trx != null);
  }
}

home_page.dart

import 'package:flutter/material.dart';
import 'package:get/get.dart';
import 'package:getx_api/src/controllers/transaction_controller.dart';


class HomePage extends StatelessWidget {
  /* ---------------------------------------------------------------------------- */
  const HomePage({Key key}) : super(key: key);
  /* ---------------------------------------------------------------------------- */
  @override
  Widget build(BuildContext context) {
    final obj = Get.put(TransactionController());

    return Scaffold(
      appBar: buildAppBar(),
      body: Obx(() => obj.dataAvailable
        ? Text(obj.trx.toString())
        : Text('... waiting ...')),
    );
  }
  /* ---------------------------------------------------------------------------- */
  AppBar buildAppBar() {
    return AppBar(
      title: Text('Hi!'),
      centerTitle: true,
    );
  }
}

transactions_data.dart

const transactionData = '''
{
    "data": [
    ....
    }
}
''';