Flutter/Dart 从 Firestore 投射到地图中

Posted 2023-02-23

【中文标题】Flutter/Dart 从 Firestore 投射到地图中

【英文标题】：Flutter/Dart casting from Firestore into map

【发布时间】：2020-03-08 07:31:46

【问题描述】：

我在将数据从 firestore 映射到模型时遇到问题。 我已经尝试了几个小时并且总是遇到像 'Map can't be cast to Map' 或 'type '_InternalLinkedHashMap' 不是类型'Map'的子类型之类的转换错误（异常） '

我尝试了这些链接中的示例：

How do you load array and object from Cloud Firestore in Flutter

https://github.com/dart-lang/sdk/issues/36836

还有很多，仍然不明白这东西是如何工作的。

这是我的实体和模型类：

实体

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:equatable/equatable.dart';

class ScreenHomeEntity extends Equatable 
  final String id;
  final String userName;
  final String userEmail;
  final String mainDoor;
  final Map<dynamic, dynamic> doors;

  const ScreenHomeEntity(
      this.id, this.userName, this.userEmail, this.mainDoor, this.doors);

  @override
  List<Object> get props => [id, userName, userEmail, mainDoor, doors];

  @override
  String toString() =>
      'ScreenHomeEntity id: $id, userName: $userName, userEmail: $userEmail, mainDoor: $mainDoor, doors: $doors';

  Map<String, Object> toJson() 
    return 
      'id': id,
      'userName': userName,
      'userEmail': userEmail,
      'mainDoor': mainDoor,
      'doors': doors,
    ;
  

  static ScreenHomeEntity fromJson(Map<String, Object> json) 
    return ScreenHomeEntity(
      json['id'] as String,
      json['userName'] as String,
      json['userEmail'] as String,
      json['mainDoor'] as String,
      json['doors'] as Map<dynamic, dynamic>,
    );
  

  Map<String, Object> toDocument() 
    return 
      'userName': userName,
      'userEmail': userEmail,
      'mainDoor': mainDoor,
      'doors': doors,
    ;
  

  static ScreenHomeEntity fromDocument(DocumentSnapshot doc) 
    return ScreenHomeEntity(
      doc.documentID,
      doc.data['userName'],
      doc.data['userEmail'],
      doc.data['mainDoor'],
      doc.data['doors'],
    );
  

型号：

import 'package:brava_flutter/data/entities/screen_home_entity.dart';
import 'package:meta/meta.dart';

@immutable
class ScreenHome 
  final String id;
  final String userName;
  final String userEmail;
  final String mainDoor;
  final Map<String, ScreenHomeDoor> doors;

  ScreenHome(this.userName,
      String userEmail = '',
      String id,
      String mainDoor,
      Map<String, ScreenHomeDoor> doors)
      : this.userEmail = userEmail ?? '',
        this.id = id,
        this.mainDoor = mainDoor ?? '',
        this.doors = doors ?? Map<String, ScreenHomeDoor>();

  ScreenHome copyWith(
    String id,
    String userName,
    String userEmail,
    String mainDoor,
    Map<String, ScreenHomeDoor> doors,
  ) 
    return ScreenHome(
      userName ?? this.userName,
      id: id ?? this.id,
      userEmail: userEmail ?? this.userEmail,
      mainDoor: mainDoor ?? this.mainDoor,
      doors: doors ?? this.doors,
    );
  

  @override
  int get hashCode =>
      id.hashCode ^
      userName.hashCode ^
      userEmail.hashCode ^
      mainDoor.hashCode ^
      doors.hashCode;

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is ScreenHome &&
          runtimeType == other.runtimeType &&
          id == other.id &&
          userName == other.userName &&
          userEmail == other.userEmail &&
          mainDoor == other.mainDoor &&
          doors == other.doors;

  @override
  String toString() =>
      'ScreenHomeModel id: $id, userName: $userName, userEmail: $userEmail, mainDoor: $mainDoor, doors: $doors';

  ScreenHomeEntity toEntity() =>
      ScreenHomeEntity(id, userName, userEmail, mainDoor, doors);

  static ScreenHome fromEntity(ScreenHomeEntity entity) 
    return ScreenHome(
      entity.userName,
      id: entity.id,
      userEmail: entity.userEmail,
      mainDoor: entity.mainDoor,
      doors: entity.doors, // EXCEPTION
    );
  


class ScreenHomeDoor 
  String name;
  String address;

  ScreenHomeDoor.fromMap(Map<dynamic, dynamic> data)
      : name = data['name'],
        address = data['address'];

firestore 数据示例：

【问题讨论】：

您遗漏了一些代码，但我发现可能存在类型不兼容的错误。你没有忘记使用你的ScreenHomeDoor.fromMap(Map<dynamic, dynamic> data) 方法吗？您可以从 Firebase 控制台显示您的 Firestore 对象结构吗？如果我了解您打算如何将您的 Map<dynamic, dynamic> 转换为 Map<String, ScreenHomeDoor>，我可以为您提供帮助

我从 Firestore 添加了图片（数据结构）。我没有忘记调用 .fromMap (ScreenHomeDoor)，我在模型类中用 'fromEntity' 调用它，这就是我得到错误的地方。

【参考方案1】：

答案：

在模型中，方法“fromEntity”我没有将实体映射（动态）转换为模型映射（对象），而这正是发生异常的地方。 这个动态映射中的每个“值”都应该被转换为对象，我一直都做错了。

  static ScreenHome fromEntity(ScreenHomeEntity entity) 
    return ScreenHome(
      entity.userName,
      id: entity.id,
      userEmail: entity.userEmail,
      mainDoor: entity.mainDoor,
      doors: entity.doors
          .map((k, v) => MapEntry(k as String, ScreenHomeDoor.fromMap(v))),
    );
  

一直以来我都在尝试使用MapEntry(k as String, v as ScreenHomeDoor.fromMap(v))

一个简单而愚蠢的错误......