Writing class for different JSON files – Shopify

I guess you can come up with an API call method (similar to which you already have done). The JSON which you are providing has different sub levels. So, you could use different classes for it. For simplification there are tools out there which converts JSON to Dart. You could look for them. Once such tool is this.

API calling would most probably be just adding it in a root element. I guess it should take care of the rest. (because the inter dependency classes are also included when converting JSON to dart)

I tried to convert your JSON (which had an extra comma in line:19) and below is the result I got.

class Element {
  List<Orders> orders;

  Element({this.orders});

  Element.fromJson(Map<String, dynamic> json) {
    if (json['orders'] != null) {
      orders = new List<Orders>();
      json['orders'].forEach((v) {
        orders.add(new Orders.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.orders != null) {
      data['orders'] = this.orders.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class Orders {
  int id;
  String adminGraphqlApiId;
  int appId;
  String browserIp;
  bool buyerAcceptsMarketing;
  Null cancelReason;
  Null cancelledAt;
  Null cartToken;
  int checkoutId;
  String checkoutToken;
  ClientDetails clientDetails;
  Null closedAt;
  bool confirmed;
  Null contactEmail;
  String createdAt;
  String currency;
  String currentSubtotalPrice;
  CurrentSubtotalPriceSet currentSubtotalPriceSet;
  String currentTotalDiscounts;
  CurrentSubtotalPriceSet currentTotalDiscountsSet;
  Null currentTotalDutiesSet;
  String currentTotalPrice;
  CurrentSubtotalPriceSet currentTotalPriceSet;
  String currentTotalTax;
  CurrentSubtotalPriceSet currentTotalTaxSet;

  Orders(
      {this.id,
      this.adminGraphqlApiId,
      this.appId,
      this.browserIp,
      this.buyerAcceptsMarketing,
      this.cancelReason,
      this.cancelledAt,
      this.cartToken,
      this.checkoutId,
      this.checkoutToken,
      this.clientDetails,
      this.closedAt,
      this.confirmed,
      this.contactEmail,
      this.createdAt,
      this.currency,
      this.currentSubtotalPrice,
      this.currentSubtotalPriceSet,
      this.currentTotalDiscounts,
      this.currentTotalDiscountsSet,
      this.currentTotalDutiesSet,
      this.currentTotalPrice,
      this.currentTotalPriceSet,
      this.currentTotalTax,
      this.currentTotalTaxSet});

  Orders.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    adminGraphqlApiId = json['admin_graphql_api_id'];
    appId = json['app_id'];
    browserIp = json['browser_ip'];
    buyerAcceptsMarketing = json['buyer_accepts_marketing'];
    cancelReason = json['cancel_reason'];
    cancelledAt = json['cancelled_at'];
    cartToken = json['cart_token'];
    checkoutId = json['checkout_id'];
    checkoutToken = json['checkout_token'];
    clientDetails = json['client_details'] != null
        ? new ClientDetails.fromJson(json['client_details'])
        : null;
    closedAt = json['closed_at'];
    confirmed = json['confirmed'];
    contactEmail = json['contact_email'];
    createdAt = json['created_at'];
    currency = json['currency'];
    currentSubtotalPrice = json['current_subtotal_price'];
    currentSubtotalPriceSet = json['current_subtotal_price_set'] != null
        ? new CurrentSubtotalPriceSet.fromJson(
            json['current_subtotal_price_set'])
        : null;
    currentTotalDiscounts = json['current_total_discounts'];
    currentTotalDiscountsSet = json['current_total_discounts_set'] != null
        ? new CurrentSubtotalPriceSet.fromJson(
            json['current_total_discounts_set'])
        : null;
    currentTotalDutiesSet = json['current_total_duties_set'];
    currentTotalPrice = json['current_total_price'];
    currentTotalPriceSet = json['current_total_price_set'] != null
        ? new CurrentSubtotalPriceSet.fromJson(json['current_total_price_set'])
        : null;
    currentTotalTax = json['current_total_tax'];
    currentTotalTaxSet = json['current_total_tax_set'] != null
        ? new CurrentSubtotalPriceSet.fromJson(json['current_total_tax_set'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['admin_graphql_api_id'] = this.adminGraphqlApiId;
    data['app_id'] = this.appId;
    data['browser_ip'] = this.browserIp;
    data['buyer_accepts_marketing'] = this.buyerAcceptsMarketing;
    data['cancel_reason'] = this.cancelReason;
    data['cancelled_at'] = this.cancelledAt;
    data['cart_token'] = this.cartToken;
    data['checkout_id'] = this.checkoutId;
    data['checkout_token'] = this.checkoutToken;
    if (this.clientDetails != null) {
      data['client_details'] = this.clientDetails.toJson();
    }
    data['closed_at'] = this.closedAt;
    data['confirmed'] = this.confirmed;
    data['contact_email'] = this.contactEmail;
    data['created_at'] = this.createdAt;
    data['currency'] = this.currency;
    data['current_subtotal_price'] = this.currentSubtotalPrice;
    if (this.currentSubtotalPriceSet != null) {
      data['current_subtotal_price_set'] =
          this.currentSubtotalPriceSet.toJson();
    }
    data['current_total_discounts'] = this.currentTotalDiscounts;
    if (this.currentTotalDiscountsSet != null) {
      data['current_total_discounts_set'] =
          this.currentTotalDiscountsSet.toJson();
    }
    data['current_total_duties_set'] = this.currentTotalDutiesSet;
    data['current_total_price'] = this.currentTotalPrice;
    if (this.currentTotalPriceSet != null) {
      data['current_total_price_set'] = this.currentTotalPriceSet.toJson();
    }
    data['current_total_tax'] = this.currentTotalTax;
    if (this.currentTotalTaxSet != null) {
      data['current_total_tax_set'] = this.currentTotalTaxSet.toJson();
    }
    return data;
  }
}

class ClientDetails {
  String acceptLanguage;
  int browserHeight;
  String browserIp;
  int browserWidth;
  Null sessionHash;

  ClientDetails(
      {this.acceptLanguage,
      this.browserHeight,
      this.browserIp,
      this.browserWidth,
      this.sessionHash});

  ClientDetails.fromJson(Map<String, dynamic> json) {
    acceptLanguage = json['accept_language'];
    browserHeight = json['browser_height'];
    browserIp = json['browser_ip'];
    browserWidth = json['browser_width'];
    sessionHash = json['session_hash'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['accept_language'] = this.acceptLanguage;
    data['browser_height'] = this.browserHeight;
    data['browser_ip'] = this.browserIp;
    data['browser_width'] = this.browserWidth;
    data['session_hash'] = this.sessionHash;
    return data;
  }
}

class CurrentSubtotalPriceSet {
  ShopMoney shopMoney;
  ShopMoney presentmentMoney;

  CurrentSubtotalPriceSet({this.shopMoney, this.presentmentMoney});

  CurrentSubtotalPriceSet.fromJson(Map<String, dynamic> json) {
    shopMoney = json['shop_money'] != null
        ? new ShopMoney.fromJson(json['shop_money'])
        : null;
    presentmentMoney = json['presentment_money'] != null
        ? new ShopMoney.fromJson(json['presentment_money'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.shopMoney != null) {
      data['shop_money'] = this.shopMoney.toJson();
    }
    if (this.presentmentMoney != null) {
      data['presentment_money'] = this.presentmentMoney.toJson();
    }
    return data;
  }
}

class ShopMoney {
  String amount;
  String currencyCode;

  ShopMoney({this.amount, this.currencyCode});

  ShopMoney.fromJson(Map<String, dynamic> json) {
    amount = json['amount'];
    currencyCode = json['currency_code'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['amount'] = this.amount;
    data['currency_code'] = this.currencyCode;
    return data;
  }
}