Question

我有一个JSON，如果其中一个属性的值不同，则返回一个重复的对象，例如：

   {
    "nid": "41",
    "news_title": "title",
    "body": "body",
    "news_image": "img1.JPG",
},
{
    "nid": "41",
    "news_title": "title",
    "body": "body",
    "news_image": "img2.JPG",
},

它们都是ID为41的同一个节点，除了唯一的news_image以外，其他数据均重复了

对象的类是：

  String nid;
  String newsTitle;
  String body;
  String newsImage;
  List<String> newsImgs;

并且正在像这样解析它：

 List<News> newsdata = (jsonResponse as List).map((i) => new News.fromJson(i));

到目前为止一切都很好..但是我还有另外一个列表：

List<News> newsList = <News>[];

我要在其中将具有相同nid的相同新闻的图像添加到列表newsImgs，然后将其添加到newsList ..因此，我不会使用相同nid和相同新闻的所有图像复制新闻将在一个列表中

该怎么做？

Answer 1

尝试列出此列表。设置仅存储唯一值。

  Set<News> newsList= new Set();
newsList.addAll(newsdata);

Answer 2

import 'dart:convert';

import 'package:queries/collections.dart';

void main() {
  var news = Collection(_readData());
  var query = news
      .select((m) => News.fromMap(m)
        ..newsImgs = news
            .where((n) => n['nid'] == m['nid'])
            .select((n) => n['news_image'] as String)
            .toList())
      .distinct(CustomEqualityComparer((e1, e2) => e1.nid == e2.nid, (n) => 0));
  print(query.toList());
}

var _data = '''
[
  {
    "nid": "41",
    "news_title": "title",
    "body": "body",
    "news_image": "img1.JPG"
  },
  {
    "nid": "41",
    "news_title": "title",
    "body": "body",
    "news_image": "img2.JPG"
  },  
  {
    "nid": "42",
    "news_title": "title",
    "body": "body",
    "news_image": "img3.JPG"
  }
]
''';

List _readData() {
  return jsonDecode(_data);
}

class News {
  String nid;
  String newsTitle;
  String body;
  String newsImage;
  List<String> newsImgs;

  News.fromMap(Map data) {
    body = data['body'] as String;
    nid = data['nid'] as String;
    newsImage = data['news_image'] as String;
    newsTitle = data['news_title'] as String;
  }

  String toString() {
    return 'nid: ${nid}, images: ${newsImgs}';
  }
}

结果：

[nid: 41, images: [img1.JPG, img2.JPG], nid: 42, images: [img3.JPG]]

另一种方式（通过分组）：

void main() {
  var news = Collection(_readData());
  var query = news.groupBy$2(
      (m) => m['nid'] as String,
      (k, v) => News.fromMap(v.firstOrDefault())
        ..newsImgs = v.select((e) => e['news_image'] as String).toList());
  print(query.toList());
}

要导入软件包queries，您需要在文件pubspec.yaml中添加以下行：

dependencies:
  queries: ^0.1.12

比较对象列表中的数据

2 个答案: