Dart: Create dynamic Class based on JSON response

Question

I need to make a class which has dynamic fields which depends on what the API returns.

I am using a custom made Rest API which returns data that does not have same number of fields in all cases. Till now I was using a class with factory constructor to create objects from the response as follows:

class MyClass {
  dynamic field1;
  dynamic field2;
  dynamic field3;
  dynamic field4;

  MyClass({
    this.field1,
    this.field2,
    this.field3,
    this.field4,
  });

  factory MyClass.fromJson(dynamic json) {
    return MyClass(
      field1: json['field1'],
      field2: json['field2'],
      field3: json['field3'],
      field4: json['field4'],
    );
  }
}

The above class works well if the response is:

{
  "field1": 123,
  "field2": 432,
  "field3": 213,
  "field4": 331
}

But this does not work in all the cases as some of the responses contain less than or more than 4 fields.

It can be:

{
  "field1": 123,
  "field2": 432,
  "field3": 213
}

OR

{
  "field1": 123,
  "field2": 432,
  "field3": 213,
  "field4": 331,
  "field5": 251
}

How can I create a dynamic class which checks how many fields are there and creates itself at runtime?

Answer 1

AFAIK, there is no way of achieving what you're asking for in Dart as of today. What you can do is:

class MyClass {
  final Map<dynamic, dynamic> data;

  MyClass(this.data);

  factory MyClass.fromJson(dynamic json) {
    assert(json is Map);
    return MyClass(json['data']);
  }
}

void main() {
  // Let's say this is your json
  final json = {
    'data': {
      'field1': 1,
      'field2': 2.2,
    },
  };

  // Create your MyClass instance
  var myClass = MyClass.fromJson(json);

  // Get the values
  var field1 = myClass.data['field1']; // prints 1
  var field2 = myClass.data['field2']; // prints 2.2
}