如何从Flutter Flow中的文档引用中获取值？

Question

我有 2 个收藏：电影、类型。在电影收藏中，存在类型作为列表参考。

在我的应用程序中，我想从收藏电影中的单个文档中获取所有流派列表值。

论点 1：某人电影的参考类型列表

参数 2：列表连接的格式分隔符

测试函数返回错误，在构建中返回默认值但引用不为空

我如何从该文档参考中获取值？

电影合集：

流派集合：

在颤振流中：

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/uploaded_file.dart';
import '/flutter_flow/custom_functions.dart';
import '/backend/backend.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

String? joinGenresFromFilm(
  List<DocumentReference>? filmGenresRef,
  String separator,
) {
  /// MODIFY CODE ONLY BELOW THIS LINE

  // get from filmGenresRef document all ru_name fields and join to string
  if (filmGenresRef == null || filmGenresRef.isEmpty) {
    return null;
  }

  List<String> genres = [];
  for (DocumentReference ref in filmGenresRef) {
    ref.get().then((snapshot) {
      if (snapshot.exists) {
        Map<String, dynamic> data = snapshot.data()! as Map<String, dynamic>;
        String ruName = data['ru_name'];
        genres.add(ruName);
      }
    });
  }
  return genres.join(separator);

  /// MODIFY CODE ONLY ABOVE THIS LINE
}

更新：

我在编辑器的测试功能中收到此错误：

Compilation error: Info: Compiling with sound null safety
lib/main.dart:23:9:
Error: The method 'get' isn't defined for the class 'DocumentReference'.
 - 'DocumentReference' is from 'package:dartpad_sample/main.dart' ('lib/main.dart').
    ref.get().then((snapshot) {

Answer 1

try it:
Future<String?> joinGenresFromFilm(
  List<DocumentReference>? filmGenresRef,
  String separator,
) async {
  /// MODIFY CODE ONLY BELOW THIS LINE

  // get from filmGenresRef document all ru_name fields and join to string
  if (filmGenresRef == null || filmGenresRef.isEmpty) {
    return null;
  }

  List<String> genres = [];
  for (DocumentReference ref in filmGenresRef) {
    DocumentSnapshot snapshot = await FirebaseFirestore.instance.doc(ref.path).get();
    if (snapshot.exists) {
      Map<String, dynamic> data = snapshot.data()! as Map<String, dynamic>;
      String ruName = data['ru_name'];
      genres.add(ruName);
    }
  }
  return genres.join(separator);

  /// MODIFY CODE ONLY ABOVE THIS LINE
}