How to parse json array into list in dart?

Question

As for the script below, I have two different json for single record and multiple record as a list. I can parse the single data using the Person class. For the json with a list, I'm using ther PersonList class but I'm getting an error because the json key result is not needed anymore. Is there a way to parse the list without changing the Person class? Or should I not use the PersonList class and just create a List<Person>?

I saw this example but its only working if the json is a whole list like this

var jsonResponse = convert.jsonDecode(rawJsonMulti) as List;
    return jsonResponse.map((p) => Person.fromJson(p).toList();

Can you show me how to use the above script using my json. Thanks.

import 'dart:convert';
void main() {

  String rawJsonMulti = '{"result": [{"name":"Mary","age":30},{"name":"John","age":25}]}';
  String rawJsonSingle = '{"result": {"name":"Mary","age":30}}';
  
// Working for non list json  
//   final result = json.decode(rawJsonSingle);
//   var obj = Person.fromJson(result);
//   print(obj.name);

  
  final result = json.decode(rawJsonMulti);
  var obj = PersonList.fromJson(result);
  print(obj.listOfPerson[0].name);

}


  class PersonList {
  final List<Person> listOfPerson;

  PersonList({this.listOfPerson});

  factory PersonList.fromJson(Map<String, dynamic> json) {
    var personFromJson = json['result'] as List;

    List<Person> lst =
        personFromJson.map((i) => Person.fromJson(i)).toList();

    return PersonList(listOfPerson: lst);
  }
}


  class Person {
    String name;
    int age;
    
    //will only work on result is not a list
    Person({this.name, this.age});
    factory Person.fromJson(Map<String, dynamic> json) {
      return Person(name: json['result']['name'],
                   age: json['result']['age']);
    }

//  This will work on json with list but not in single
//  factory Person.fromJson(Map<String, dynamic> json) {
//       return Person(name: json['name'],
//                    age: json['age']);
//     }
    

  }

So you want the code to support both rawJsonMulti and rawJsonSingle ? — julemand101
– julemand101, Commented Jul 14, 2020 at 15:16

Matthiee · Accepted Answer · 2022-01-25 05:47:47Z

1

If you convert the dynamic to a List<dynamic> you can map each element in the jsonDecoded list.

Example:

import 'dart:convert';

final decodedJson = jsonDecode(rawJsonMulti) as List<dynamic>;
final personList = decodedJson
    .map((e) => Person.fromJson(
        e as Map<String, dynamic>))
    .toList();

return PersonList(listOfPerson: personList);
```

answered Jan 25, 2022 at 5:47

Matthiee

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Comments

julemand101 · Accepted Answer · 2020-07-14 15:25:53Z

Try take a look at this solution where I have fixed your code:

import 'dart:convert';

void main() {
  const rawJsonMulti =
      '{"result": [{"name":"Mary","age":30},{"name":"John","age":25}]}';
  const rawJsonSingle = '{"result": {"name":"Mary","age":30}}';

  final resultMulti = json.decode(rawJsonMulti) as Map<String, dynamic>;
  final personListMulti = PersonList.fromJson(resultMulti);
  print(personListMulti.listOfPerson[0]); // Mary (age: 30)
  print(personListMulti.listOfPerson[1]); // John (age: 25)

  final resultSingle = json.decode(rawJsonSingle) as Map<String, dynamic>;
  final personListSingle = PersonList.fromJson(resultMulti);
  print(personListSingle.listOfPerson[0]); // Mary (age: 30)
}

class PersonList {
  final List<Person> listOfPerson;

  PersonList({this.listOfPerson});

  factory PersonList.fromJson(Map<String, dynamic> json) {
    if (json['result'] is List) {
      final personsFromJson = json['result'] as List;
      return PersonList(listOfPerson: [
        ...personsFromJson
            .cast<Map<String, Object>>()
            .map((i) => Person.fromJson(i))
      ]);
    } else {
      final personFromJson = json['result'] as Map<String, Object>;
      return PersonList(listOfPerson: [Person.fromJson(personFromJson)]);
    }
  }
}

class Person {
  String name;
  int age;

  Person({this.name, this.age});
  factory Person.fromJson(Map<String, dynamic> json) {
    return Person(name: json['name'] as String, age: json['age'] as int);
  }

  @override
  String toString() => '$name (age: $age)';
}

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