Firestore QuerySnapshot转List<Map>再转Item对象列表求助

需要把Firestore查询返回的QuerySnapshot转换为List<Map<String,dynamic>>，再进一步转为Item对象列表，现有代码如下：

现有Cubit代码 #

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:htu_app/models/item.dart';

class categoryCubit extends Cubit<List<Item>> {
  categoryCubit() : super([]);

  Future<void> getItemsFromCategory({required String category}) async {
    QuerySnapshot docs = await FirebaseFirestore.instance
        .collection('items')
        .where('category', isEqualTo: category)
        .get();
  }
}

现有Item类代码 #

class Item {
  Item(
      {required this.name,
      required this.price,
      required this.category,
      required this.date,
      required this.pic});

  String name;
  double price;
  String category;
  String date;
  String pic;

  factory Item.fromJson(Map<String, dynamic> json) => Item(
      name: json['name'],
      price: json['price'],
      category: json['category'],
      date: json['json'], // 此处存在笔误
      pic: json['pic']);
}

解决方案 #

首先修正Item类的fromJson方法笔误，将date: json['json']改为date: json['date']，同时添加类型断言确保类型安全。

然后在getItemsFromCategory方法中完成三步转换：提取文档数据为Map列表、转为Item对象列表、更新Cubit状态。

修正后的Item类

class Item {
  Item(
      {required this.name,
      required this.price,
      required this.category,
      required this.date,
      required this.pic});

  String name;
  double price;
  String category;
  String date;
  String pic;

  factory Item.fromJson(Map<String, dynamic> json) => Item(
      name: json['name'] as String,
      price: (json['price'] as num).toDouble(), // 处理Firestore数字类型转double
      category: json['category'] as String,
      date: json['date'] as String,
      pic: json['pic'] as String);
}

更新后的Cubit代码

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:htu_app/models/item.dart';

class categoryCubit extends Cubit<List<Item>> {
  categoryCubit() : super([]);

  Future<void> getItemsFromCategory({required String category}) async {
    QuerySnapshot docs = await FirebaseFirestore.instance
        .collection('items')
        .where('category', isEqualTo: category)
        .get();
    
    // 将QuerySnapshot转为Map列表
    List<Map<String, dynamic>> itemsMapList = docs.docs
        .map((doc) => doc.data() as Map<String, dynamic>)
        .toList();
    
    // 将Map列表转为Item对象列表
    List<Item> itemsList = itemsMapList
        .map((itemMap) => Item.fromJson(itemMap))
        .toList();
    
    // 发射更新后的列表状态
    emit(itemsList);
  }
}

关键说明 #

• QuerySnapshot的docs属性包含所有查询到的文档快照（QueryDocumentSnapshot）；
• 每个文档快照的data()方法直接返回文档的键值对Map；
• Firestore中存储的数字默认是num类型，需要转为double匹配Item类的price字段；
• 添加类型断言（as String/as num）可以避免运行时类型错误。

内容的提问来源于stack exchange，提问作者Zain Erikat