Flutter Parsing Complex Json

Question

I am having some difficulties with parsing the JSON from API. Previously the JSON format was simpler:

        {   "author": {
                "id": 4,
                "username": "maria"
             },
            "description": "dsada",
            "image": "/media/posts/image_cropper_1616320457204.jpg",
            "created_at": "2021-03-21T09:54:38.645596Z"
        },
        {
            "author": {
                "id": 4,
                "username": "maria"
            },
            "description": "asdsad",
            "image": "/media/posts/image_cropper_1616070403137.jpg",
            "created_at": "2021-03-18T12:26:56.774797Z"
        }

And my model for that JSON format was the following

class Feed {
  final String author;
  final String description;
  final String imageUrl;
  final String createdAt;

  Feed({this.author, this.description, this.imageUrl, this.createdAt});

  factory Feed.fromJson(Map<String, dynamic> json) {
    return Feed(
      author: json['author']['username'],
      description: json['description'],
      imageUrl: json['image'],
      createdAt: json['created_at'],
    );
  }
}

Recently the API was changed slightly to enable pagination. After that the I couldn't figure out a way to properly get that data from API in a correct format. New JSON format looks like this:

{
  'count: 6,
  'next': "/posts/list/?limit=5&offset=5",
  'previous': null,'
  'results': [
      {   "author": {
                "id": 4,
                "username": "maria"
             },
            "description": "dsada",
            "image": "/media/posts/image_cropper_1616320457204.jpg",
            "created_at": "2021-03-21T09:54:38.645596Z"
        },
        {
            "author": {
                "id": 4,
                "username": "maria"
            },
            "description": "asdsad",
            "image": "/media/posts/image_cropper_1616070403137.jpg",
            "created_at": "2021-03-18T12:26:56.774797Z"
        }
   ]
   
}

I didn't think that after adding pagination the JSON format would change. If you have any idea to do this, kindly help. Thank you.

Felipe Vergara · Accepted Answer · 2021-03-23 20:47:51Z

2

To create your classes quickly you can use this application that could help you in the beginning, then you can make the modifications if necessary. (https://app.quicktype.io/)

class User {
    User({
        this.count,
        this.next,
        this.previous,
        this.results,
    });

    final int count;
    final String next;
    final dynamic previous;
    final List<Result> results;

    factory User.fromJson(Map<String, dynamic> json) => User(
        count: json["count"],
        next: json["next"],
        previous: json["previous"],
        results: List<Result>.from(json["results"].map((x) => Result.fromJson(x))),
    );

    Map<String, dynamic> toJson() => {
        "count": count,
        "next": next,
        "previous": previous,
        "results": List<dynamic>.from(results.map((x) => x.toJson())),
    };
}


class Result {
    Result({
        this.author,
        this.description,
        this.image,
        this.createdAt,
    });

    final Author author;
    final String description;
    final String image;
    final DateTime createdAt;

    factory Result.fromJson(Map<String, dynamic> json) => Result(
        author: Author.fromJson(json["author"]),
        description: json["description"],
        image: json["image"],
        createdAt: DateTime.parse(json["created_at"]),
    );

    Map<String, dynamic> toJson() => {
        "author": author.toJson(),
        "description": description,
        "image": image,
        "created_at": createdAt.toIso8601String(),
    };
}

class Author {
    Author({
        this.id,
        this.username,
    });

    final int id;
    final String username;

    factory Author.fromJson(Map<String, dynamic> json) => Author(
        id: json["id"],
        username: json["username"],
    );

    Map<String, dynamic> toJson() => {
        "id": id,
        "username": username,
    };
}

answered Mar 23, 2021 at 20:47

Felipe Vergara

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2 Comments

Davrick Over a year ago

Thank you for the answer. But in this case how do I get the data inside Feed screen ? With my previous code I was getting it through List<Feed> feeds = await DatabaseService.getPosts(); since they were all in one format.

Felipe Vergara Over a year ago

@Davrick First of all in the solution that I provide you could modify the class name from Author to Feed. After doing that and if I implement the other classes as recommended, it will no longer receive a List of type Feed (List<Feed>), but rather an instance of type Feed (Feed), which then in the widget you can invoke the list as follows: Feed.results

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