Firebase Flutter Riverpod：映射模型时如何获取Firebase自动生成的documentID

你遇到的报错本质是两个问题导致的：

1. Firebase自动生成的documentID不存在于文档字段数据中，它是QueryDocumentSnapshot对象本身自带的id属性，不会出现在e.data()返回的Map里
2. 工厂构造方法中你写的restaurantModel[documentID]是试图用还未初始化的类实例属性documentID作为key取值，自然会触发报错

第一步：修改Model层工厂构造 #

给fromFirebase方法新增id入参，用来接收Service层传递的文档ID：

import 'package:cloud_firestore/cloud_firestore.dart';

class RestaurantModel {
  final String? name;
  final String? phone;
  final String? fullAddress;
  final String? yearsInBusiness;
  final String? priceRange;
  final String? websiteLink;
  final String? documentID;

  RestaurantModel({
    required this.name,
    required this.phone,
    required this.fullAddress,
    required this.yearsInBusiness,
    required this.priceRange,
    required this.websiteLink,
    required this.documentID,
  });

  factory RestaurantModel.fromFirebase(Map<String, dynamic> restaurantModel, String documentId) {
    return RestaurantModel(
        name: restaurantModel['name'],
        phone: restaurantModel['phone'],
        fullAddress: restaurantModel['fullAddress'],
        yearsInBusiness: restaurantModel['yearsInBusiness'],
        priceRange: restaurantModel['priceRange'],
        websiteLink: restaurantModel['websiteLink'],
        // 直接用传入的id赋值即可
        documentID: documentId,
    );
  }
}

第二步：修改Service层映射逻辑 #

调用工厂方法时，把QueryDocumentSnapshot自带的id属性作为第二个参数传入：

Stream<List<RestaurantModel>> restaurantModel() {
  return _firebase.collection('restaurantsPensacola').snapshots().map((event) => 
    event.docs.map((e) => RestaurantModel.fromFirebase(e.data(), e.id)).toList()
  );
}

可选优化方案：直接传递整个快照对象到工厂方法，代码更简洁
Model层工厂构造修改为：

factory RestaurantModel.fromFirebase(QueryDocumentSnapshot snapshot) {
  Map<String, dynamic> data = snapshot.data() as Map<String, dynamic>;
  return RestaurantModel(
    name: data['name'],
    phone: data['phone'],
    fullAddress: data['fullAddress'],
    yearsInBusiness: data['yearsInBusiness'],
    priceRange: data['priceRange'],
    websiteLink: data['websiteLink'],
    documentID: snapshot.id,
  );
}

对应Service层调用改为：

event.docs.map((e) => RestaurantModel.fromFirebase(e)).toList()

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