Question

嗨，我正在构建一个应用程序，并尝试从api回调中解析嵌套的对象数组并收到此错误

类型字符串不是Map的子类型<字符串，动态>

这是模型课

/*function call : 
                    select * from fn_return_pivot() ;
*/
create or replace function fn_return_pivot() 
returns table(srno bigint , D text, N text , X text , F text, C text)
as 
$$
declare v_query text ;
begin 

v_query = (SELECT T.sql FROM (SELECT 'SELECT *
FROM   crosstab(
       $ct$SELECT u.attnum, t.rn, u.val
        FROM  (SELECT row_number() OVER () AS rn, * FROM '
                              || attrelid::regclass || ') t
             , unnest(ARRAY[' || string_agg(quote_ident(attname)
                              || '::text', ',') || '])
                 WITH ORDINALITY u(val, attnum)
        ORDER  BY 1, 2$ct$
   ) t (attnum bigint, '
     || (SELECT string_agg('r'|| rn ||' text', ', ')
         FROM  (SELECT row_number() OVER () AS rn FROM "COUNT SHIFTS") t)
     || ')' AS sql
FROM   pg_attribute
WHERE  attrelid = '"COUNT SHIFTS"'::regclass
AND    attnum > 0
AND    NOT attisdropped
GROUP  BY attrelid) AS T );

return query execute v_query ;

end ;
$$
language plpgsql ;

这是我收到的json回调

class Tournament {
  String id;
  String title;
  String roomID;
  String roomPass;
  String map;
  String type;
  String date;
  String time;
  int joined;
  String createdBy;
  List<UserIds> joinedUsers;

  Tournament(
      {this.createdBy,
      this.joinedUsers,
      this.id,
      this.date,
      this.map,
      this.roomID,
      this.roomPass,
      this.time,
      this.title,
      this.type,
      this.joined});

  factory Tournament.fromJson(Map<String, dynamic> json) {
    var list = json['joinedUsers'] as List;
    List<UserIds> userList =
        list.map((data) => UserIds.fromJson(data)).toList();

    return Tournament(
        id: json['_id'],
        title: json['title'],
        roomID: json['roomId'],
        roomPass: json['roomPass'],
        map: json['mapType'],
        type: json['type'],
        date: json['date'],
        time: json['time'],
        joined: json['joined'],
        createdBy: json['createdBy'],
        joinedUsers: userList);
  }
}

class UserIds {
  String userId;

  UserIds({this.userId});

  factory UserIds.fromJson(Map<String, dynamic> parsedJson) {
    return UserIds(userId: parsedJson['\$oid']);
  }
}

现在，当我运行它时，它给了我一个错误，提示类型String不是Map 的子类型。我不知道我现在在做什么错

Answer 1

您可以尝试：

list.map((data) => UserIds.fromJson(JSON.parse(data)).toList();

可能是解析问题，您可以通过此操作先将元素记录到lambda中，以验证其提供的内容：

list.map((element) =>
{
  console.log(data);
  //UserIds.fromJson(JSON.parse(data)).toList();
});

Answer 2

只需检查一下我为userId制作的示例：我已经在本地获取了您的json。

import 'dart:convert';

import 'package:flutter/material.dart';


void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: HomePage());
  }
}

class UserIds {
  String userId;

  UserIds({this.userId});
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  bool _isLoading = false;

  List<UserIds> userIdsList = List();

  @override
  void initState() {
    super.initState();
    getData();
  }

  getData() async {
   
    String data =
        await DefaultAssetBundle.of(context).loadString("json/parse.json");

    Map jsonData = json.decode(data);

    jsonData['joinedUsers'].forEach((item) {
      item.forEach((key, value) {
        print('This is the Key $key  value $value');
        userIdsList.add(UserIds(userId: value));
      });
    });

    print('This is the list ${userIdsList.length}');

   
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(body: Text(''));
  }
}

扑嵌套对象解析的嵌套json数组

2 个答案: