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?

Save the fields in a List or Map if the amount of fields are dynamic. — julemand101
– julemand101, Commented May 21, 2020 at 20:13
I know that's a way, but not looking for it. I need objects with easy property access. Im looking for something like reflection in java. — user321553125
– user321553125, Commented May 21, 2020 at 21:01
The purpose of classes is to have a defined interface you can use in other classes or methods. But if you classes are dynamically build on runtime with a dynamic number of methods. How are you then going to use this class in your programming? Can you give an example of how you want this to work in pseudocode? — julemand101
– julemand101, Commented May 21, 2020 at 21:08

CopsOnRoad · Accepted Answer · 2020-05-25 05:08:32Z

14

+50

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
}

edited May 25, 2020 at 5:08

answered May 25, 2020 at 4:58

CopsOnRoad

271k97 gold badges702 silver badges471 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Dart: Create dynamic Class based on JSON response

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related