Question 75626 in Flutter Question posted in
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How to use toJson and fromJson method to map through a cart in Firestore – Flutter

I have a cart and I want to assign my cart items to my _items variable inside my Provider.
This is my method. I don’t know if I should use toJson() or fromJson() methods:

This is the variable and the function inside the provider:

Map<String, CartItem> _items = {};
void getItems()async {
    var newItems = await FirebaseFirestore.instance.collection("users").doc(userId).collection("Cart").get();
    _items = newItems; // The error occurs here
}

Error:

A value of type ‘QuerySnapshot<Map<String, dynamic>>’ can’t be assigned to a variable of type ‘Map<String, CartItem>’.
Try changing the type of the variable, or casting the right-hand type to ‘Map<String, CartItem>’.

CartModel.dart

class CartItem {
  String? id;
  String? title;
  String? price;
  int? qty;
  String? image;

  CartItem({
    required this.id,
    required this.title,
    required this.price,
    required this.qty,
    required this.image,
  });

  CartItem.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    title = json['title'];
    image = json['image'];
    price = json['price'];
    qty = json['qty'] as int;
    // totalprice = double.parse(json['totalprice']);
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['title'] = this.title;
    data['image'] = this.image;
    data['price'] = this.price;
    data['qty'] = this.qty;
    // data['totalprice'] = this.totalprice;

    return data;
  }
}

Because I want to use it here (no space to. I will share a snippet):

Enter image description here

Tags:

2

Answers


  1. 0

    I think toJson is if you’re trying to send it out as json. From json is if you expect to receive that data (like an API get request).

    The error comes from you declaring _items to be of type Map<String, CartItem> but in the CartModel class, it is expected to come in as as Map of string to string.

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  2. 0
    1. Your fromjson method should return a class instance.
    2. You are not converting your firebase output.

    Below is your updated class:

    class CartItem {
  String? id;
  String? title;
  String? price;
  int? qty;
  String? image;

  CartItem({
    required this.id,
    required this.title,
    required this.price,
    required this.qty,
    required this.image,
  });

  factory CartItem.fromJson(Map<String, dynamic> json) {
   
    return CartItem(
    id: json['id'],
    title: json['title'],
    image: json['image'],
    price: json['price'],
    qty: json['qty'] as int,
);
    // totalprice = double.parse(json['totalprice']);
  }

  Map<String,dynamic> toJson(){
    final Map<String,dynamic> data = new Map<String,dynamic>();
    data['id'] = this.id;
    data['title'] = this.title;
    data['image'] = this.image;
    data['price'] = this.price;
    data['qty'] = this.qty;
    // data['totalprice'] = this.totalprice;

    return data;
  }
}

    A value of type ‘QuerySnapshot<Map<String, dynamic>>’ can’t be assigned to a variable of type ‘Map<String, CartItem>’.

    Now to fix the above error, we have to convert QuerySnapshot<Map<String, dynamic>> to Map<String, CartItem>.

    Note: I’ll use List<CartItem> instead of Map<String, CartItem>.

    List<CartItem> _items = [];

void getItems()async{
    var newItems = await FirebaseFirestore.instance.collection("users").doc(userId).collection("Cart").get();
 for (var element in newItems.docs){
 _items.add(CartItem.fromJson(element.data());
  
}

    This code was not tested.

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