(Flutter Firestore) DocumentSnapshotPlatform 中不存在字段

Question

我在尝试从子集合中检索数据时遇到错误。 firestore db如下-> users；文档 uid；消息；批准的贷款；贷款获批。

我仔细检查了我输入的文档和集合是否正确，所以我错过了什么？

任何建议将不胜感激。

谢谢

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

class MessagesScreen extends StatefulWidget {
  @override
  MessagesScreenState createState() => MessagesScreenState();
}

FirebaseAuth _auth = FirebaseAuth.instance;
final uid = _auth.currentUser!.uid;
var boldFont = TextStyle(fontFamily: 'Inter', fontWeight: FontWeight.w600);

class MessagesScreenState extends State<MessagesScreen> {
  final db = FirebaseFirestore.instance
      .collection('users')
      .doc(uid)
      .collection('Messages')
      .snapshots();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          titleSpacing: 30,
          automaticallyImplyLeading: false,
          backgroundColor: Color.fromRGBO(1, 67, 55, 1),
          toolbarHeight: 100,
          title: new Text(
            'Messages',
            style: TextStyle(
                color: Color.fromRGBO(255, 255, 255, 1),
                fontFamily: 'Poppins',
                fontSize: 25,
                letterSpacing: 1.2,
                fontWeight: FontWeight.bold,
                height: 1),
          ),
        ),
        body: StreamBuilder<QuerySnapshot>(
          stream: db,
          builder: (context, snapshot) {
            if (!snapshot.hasData)
              return const Center(
                child: CircularProgressIndicator(),
              );
            return ListView.builder(
                itemCount: snapshot.data!.docs.length,
                itemBuilder: (BuildContext context, int index) {
                  return snapshot.data!.docs[index]['Loans approved']
                      ['Loans overdue']['Loans paid'];
                });
          },
        ));
  }
}

Answer 1

原因是您将 Stream（您的 db 变量）定义为

FirebaseFirestore.instance
      .collection('users')
      .doc(uid)
      .collection('Messages')
      .snapshots();

根据您的屏幕截图，此Messages 集合中有一个Loans approved 文档没有任何数据。该文档有一个Loans approved 子集合，而该子集合又包含一个Loans approved 文档。正是此文档包含字段（Interest、Loan amount 等）。

因此，如下定义您的 Stream 应该可以解决问题：

FirebaseFirestore.instance
      .collection('users')
      .doc(uid)
      .collection('Messages')
      .doc('Loans approved')
      .collection('Loans approved')
      .snapshots();

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PS：我建议您在编写集合、文档和字段名称时使用camelCase convention。