Parse an object inside an object with Flutter and JSON API

Question

I am trying to get the link of an image from a REST service I already built. This is the result of the GET:

{
    "products": {
        "_id": "60abddf1413e7c408c103f6a",
        "product_image": "www.google.com",
        "createdAt": "2021-05-24T17:10:09.738Z",
        "__v": 0
    }
}

And this is my code of a route calling this GET service within flutter:

import 'package:flutter/material.dart';
import 'dart:async';
import 'dart:convert';

import 'package:http/http.dart' as http;

Future<Album> fetchAlbum() async {
  final response =
      await http.get(Uri.parse('http://10.0.2.2:3000/product/last'));

  if (response.statusCode == 200) {
    return Album.fromJson(jsonDecode(response.body));
  } else {
    throw Exception('Failed to load album');
  }
}

class Product {
  final String product_image;
  final String createdAt;

  Product({
    this.product_image,
    this.createdAt
  });

  factory Product.fromJson(Map<String, dynamic> json) {
    return Product(
      product_image: json['product_image'],
      createdAt: json['createdAt']
    );
  }
}

class Album {
  final Product products;

  Album({
    this.products,
  });

  factory Album.fromJson(Map<String, dynamic> json) {
    return Album(
      products: json['products']
    );
  }
}

class PromotionsPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {

    final arg = ModalRoute.of(context).settings.arguments;
    Future<Album> futureAlbum = fetchAlbum();

    return Scaffold(
      appBar: AppBar(
        title: Text('Promotions Page'),
      ),
      body: Center(
          child: FutureBuilder<Album>(
            future: futureAlbum,
            builder: (context, snapshot) {
              if (snapshot.hasData) {
                return Text(snapshot.data.products.product_image);
              } else if (snapshot.hasError) {
                return Text("${snapshot.error}");
              }

              // By default, show a loading spinner.
              return CircularProgressIndicator();
            },
          ),
        ),
    );
  }
}

but keeps throwing the error, and I don't understand very well why. I think is something related to the parsing section, an object inside another object, but I don't understand what I am doing wrong.

Christopher Moore · Accepted Answer · 2021-05-24 19:27:51Z

1

You're not calling your Product.fromJson constructor in your Album.fromJson constructor. json['products'] is a Map and you're trying to assign it to a Product.

Call Product.fromJson:

factory Album.fromJson(Map<String, dynamic> json) {
  return Album(
    products: Product.fromJson(json['products']),
  );
}

answered May 24, 2021 at 19:27

Christopher Moore

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3 Comments

Feber Castellon Over a year ago

You are awesome, thank you very much. I thought since I defined it in the constructor I should not set it up like that again. Thank you.

Christopher Moore Over a year ago

@FeberCastellon Please accept the answer if it solved your problem.

Feber Castellon Over a year ago

Yes, its just that I was waiting a few minutes, couldnt do it before.

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