Flutter中如何通过Firestore的bookmark集合文档ID查询question集合文档

方案1：嵌套StreamBuilder（实现简单，适合书签数量少的场景） #

你可以直接在列表项中嵌套StreamBuilder实现需求，外层StreamBuilder拉取当前用户的所有书签记录，拿到每条书签的文档ID后，在列表项内部监听对应question文档的变化即可。
核心修改部分为ListView.builder的itemBuilder逻辑，完整修改后的代码如下：

// 其余代码保持不变
child: ListView.builder(
  shrinkWrap: true,
  itemCount: snapshot.data!.docs.length,
  itemBuilder: (context, int index) {
    final DocumentSnapshot bookmarkDoc = snapshot.data!.docs[index];
    // 书签文档ID与对应问题ID完全一致
    final String questionId = bookmarkDoc.id;
    // 嵌套StreamBuilder拉取对应问题数据
    return StreamBuilder<DocumentSnapshot>(
      stream: FirebaseFirestore.instance.collection('question').doc(questionId).snapshots(),
      builder: (context, questionSnapshot) {
        if (questionSnapshot.connectionState == ConnectionState.waiting) {
          return const Padding(
            padding: EdgeInsets.symmetric(vertical: 16),
            child: CupertinoActivityIndicator(),
          );
        }
        if (questionSnapshot.hasError || !questionSnapshot.hasData || !questionSnapshot.data!.exists) {
          // 对应问题已删除，可按需展示占位或者自动清理无效书签
          return const SizedBox.shrink();
        }
        final questionData = questionSnapshot.data!.data() as Map<String, dynamic>;
        // 按需渲染问题字段，替换为你question集合的实际字段名
        return ListTile(
          title: Text(questionData['title']),
          subtitle: Text(questionData['content']),
          onTap: () => Navigator.push(
            context,
            MaterialPageRoute(builder: (context) => DetailsPage(questionData: questionData)),
          ),
        );
      },
    );
  },
)

方案2：批量关联查询（性能更优，适合书签数量多的场景） #

嵌套StreamBuilder会为每个列表项发起独立请求，书签数量较多时性能较差，你可以提前对数据做关联转换，仅用两次请求即可拿到所有关联的问题数据，无需嵌套。
完整实现代码如下：

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:devcom/screens/detailsPage.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

class Bookmark extends StatefulWidget {
  final User user;
  const Bookmark({Key? key, required this.user}) : super(key: key);

  @override
  State<Bookmark> createState() => _BookmarkState();
}

class _BookmarkState extends State<Bookmark> {
  late User _currentUser;
  late final Stream<List<DocumentSnapshot>> _questionStream;

  @override
  void initState() {
    _currentUser = widget.user;
    // 对流做转换，先拉书签ID再批量查对应问题
    _questionStream = FirebaseFirestore.instance
        .collection('bookmark')
        .where("uid", isEqualTo: _currentUser.uid)
        .snapshots()
        .asyncMap((bookmarkSnapshot) async {
          final questionIds = bookmarkSnapshot.docs.map((doc) => doc.id).toList();
          if (questionIds.isEmpty) return <DocumentSnapshot>[];
          // 注意：whereIn单次最多支持30个ID，超过30个需要拆分分批查询
          final questionSnapshot = await FirebaseFirestore.instance
              .collection('question')
              .where(FieldPath.documentId, whereIn: questionIds)
              .get();
          return questionSnapshot.docs;
        });
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<List<DocumentSnapshot>>(
      stream: _questionStream,
      builder: (BuildContext context, AsyncSnapshot<List<DocumentSnapshot>> snapshot) {
        if (snapshot.hasError) {
          return const Text('Something went wrong');
        }
        if (!snapshot.hasData) {
          return Text('Howdy ${_currentUser.displayName}!!, 404 clever: you havent posted in a while');
        }
        if (snapshot.connectionState == ConnectionState.waiting) {
          return const Text("Loading");
        }
        final questionList = snapshot.data!;
        return Scaffold(
          appBar: AppBar(
            title: const Text('My Questions'),
            leading: IconButton(
              onPressed: () => Navigator.pop(context),
              icon: const Icon(Icons.arrow_back_ios_new_rounded),
            ),
          ),
          backgroundColor: Colors.white,
          body: Padding(
            padding: const EdgeInsets.all(40),
            child: ListView.builder(
              shrinkWrap: true,
              itemCount: questionList.length,
              itemBuilder: (context, int index) {
                final questionData = questionList[index].data() as Map<String, dynamic>;
                return ListTile(
                  title: Text(questionData['title']),
                  subtitle: Text(questionData['content']),
                  onTap: () => Navigator.push(
                    context,
                    MaterialPageRoute(builder: (context) => DetailsPage(questionData: questionData)),
                  ),
                );
              },
            ),
          ),
        );
      },
    );
  }
}

注意事项 #

• 如果书签数量超过30，需要将ID数组拆分为多个长度为30的子数组，分别查询后合并结果
• 若对应问题被删除，可在检测到无效数据时自动删除对应的书签记录，避免脏数据

内容的提问来源于stack exchange，提问作者Mithson