FlutterFlow自定义函数调用Firebase查询获取用户名失败求助

问题根源 #

你的代码存在两个核心问题：

1. 异步操作逻辑错误：Firestore查询是异步操作，你用then回调处理结果，但函数会直接返回初始的空字符串，等异步操作完成时函数已经执行完毕，无法更新返回值。
2. FlutterFlow环境适配问题：在FlutterFlow自定义函数中，不能直接使用FirebaseFirestore.instance，需要使用平台内置的后端API来操作Firebase。

正确实现代码 #

在FlutterFlow中，需要将函数改为异步类型，并调用内置的Firestore操作方法：

import 'dart:convert';
import 'dart:math' as math;

import 'package:flutter/material.dart';
import 'package:google_fonts/google_fonts.dart';
import 'package:intl/intl.dart';
import 'package:timeago/timeago.dart' as timeago;
import '../../flutter_flow/lat_lng.dart';
import '../../flutter_flow/place.dart';
import '../../flutter_flow/custom_functions.dart';
import '../../backend/backend.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import '../../auth/auth_util.dart';

Future<String?> userToNameFxn(DocumentReference? usr) async {
  /// MODIFY CODE ONLY BELOW THIS LINE
  if (usr == null) return '';
  
  // 直接通过传入的DocumentReference获取用户文档
  final userDocSnapshot = await usr.get();
  if (userDocSnapshot.exists) {
    return userDocSnapshot.data()?['display_name'] as String? ?? '';
  }

  // 如果传入的引用对应的是uid而非文档ID，可启用以下查询逻辑
  // final querySnapshot = await usersCollection.where('uid', isEqualTo: usr.id).get();
  // if (querySnapshot.docs.isNotEmpty) {
  //   return querySnapshot.docs.first.data()['display_name'] as String? ?? '';
  // }
  
  return '';
  /// MODIFY CODE ONLY ABOVE THIS LINE
}

关键修改说明 #

• 改为异步函数：返回类型设为Future<String?>，添加async关键字，用await等待Firestore操作完成，确保拿到结果后再返回。
• 直接使用传入的引用：如果usr是用户文档的直接引用，无需额外查询，直接调用get()获取文档数据即可。
• 空值安全处理：增加usr == null的判断，避免空指针异常；文档不存在或字段为空时返回默认空字符串。

原问题详情 #

我想在FlutterFlow的自定义函数里用Dart代码查询Firebase，实现一个接收DocumentReference参数、返回对应用户display_name字符串的函数，但试了多种写法都报错，发现FlutterFlow无法识别Firebase库。

错误截图 #

尝试的第一段代码 #

import 'dart:convert';
import 'dart:math' as math;

import 'package:flutter/material.dart';
import 'package:google_fonts/google_fonts.dart';
import 'package:intl/intl.dart';
import 'package:timeago/timeago.dart' as timeago;
import '../../flutter_flow/lat_lng.dart';
import '../../flutter_flow/place.dart';
import '../../flutter_flow/custom_functions.dart';
import '../../backend/backend.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import '../../auth/auth_util.dart';

String? userToNameFxn(DocumentReference? usr) {
  /// MODIFY CODE ONLY BELOW THIS LINE

  var tmp = '';

  // Get a reference to the Firestore database
  //final _db = FirebaseFirestore.instance;

  // Get a reference to the "users" collection
  //CollectionReference users = _db.collection('users');

  // Define the ID of the user you want to retrieve
  String userId = "$usr?.id";

  // Retrieve the user with the specified ID
  /*DocumentReference user = users.document(userId);
  user.get().then((DocumentSnapshot snapshot) {
    // Print the user data
    tmp = snapshot.data as String;
  });

  final db = FirebaseFirestore.instance;
  db
      .collection("users")
      .where("uid", isEqualTo: userId)
      .snapshots()
      .listen((event) {
    tmp = event.docs[0].data()["display_name"];
  });*/

  // Get a reference to the Firestore database
  var db = FirebaseFirestore.instance;

  // Create a reference to the "users" table
  var usersRef = db.collection('users');

  // Create a query to filter the documents by the "uid" field
  var query = usersRef.where('uid', isEqualTo: userId);

  // Get the first matching document
  query.get().then((querySnapshot) {
    if (querySnapshot.size > 0) {
      // There is a matching document, so you can get the data from the first result
      var firstResult = querySnapshot.docs[0];
      var data = firstResult.data();

      // Get the display_name field from the data
      var displayName = data['display_name'];
      tmp = displayName;
      // Do something with the display_name...
    } else {
      // There are no matching documents

      tmp = '';
    }
  });

  return tmp;

  /// MODIFY CODE ONLY ABOVE THIS LINE
}

尝试的第二段代码 #

import 'dart:convert';
import 'dart:math' as math;

import 'package:flutter/material.dart';
import 'package:google_fonts/google_fonts.dart';
import 'package:intl/intl.dart';
import 'package:timeago/timeago.dart' as timeago;
import '../../flutter_flow/lat_lng.dart';
import '../../flutter_flow/place.dart';
import '../../flutter_flow/custom_functions.dart';
import '../../backend/backend.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import '../../auth/auth_util.dart';

String? userToNameFxn(DocumentReference? usr) {
  /// MODIFY CODE ONLY BELOW THIS LINE

  // Get a reference to the Firestore database
  final db = FirebaseFirestore.instance;

  // Create a reference to the "users" table
  var usersRef = db.collection('users');

  // Create a query to filter the documents by the "uid" field
  var query = usersRef.where('uid', isEqualTo: usr?.id);

  // Get the first matching document
  query.get().then((querySnapshot) {
    if (querySnapshot.size > 0) {
      // There is a matching document, so you can get the data from the first result
      var firstResult = querySnapshot.docs[0];
      var data = firstResult.data();

      // Get the display_name field from the data
      var displayName = data['display_name'];
      return displayName;
    }
  });
  return '';

  /// MODIFY CODE ONLY ABOVE THIS LINE
}

测试函数时的错误截图 #

内容的提问来源于stack exchange，提问作者Youssof