Flutter应用如何从Firebase实时数据库查询匹配当前日期的数据

核心实现逻辑 #

你要筛选和指定日期匹配的记录，只需要在现有排序查询的基础上追加equalTo匹配条件即可，具体实现如下：

1. 修改查询逻辑 #

在initState方法中，已经生成了和数据库date字段格式一致的today字符串，直接将其作为匹配条件传入查询即可：

@override
void initState() {
  super.initState();
  String today = formatter.format(now);
  _ref = FirebaseDatabase.instance
      .reference()
      .child('Daily Verse')
      .orderByChild('date')
      // 新增匹配条件，只返回date等于今日的记录
      .equalTo(today);
}

2. （可选）适配指定日期查询 #

如果需要查询非今日的其他日期，只需要给页面新增一个入参接收指定的DateTime，替换掉代码中的now变量即可：

class ReadPromise extends StatefulWidget {
  // 新增可选参数，不传默认查今日
  final DateTime? targetDate;
  const ReadPromise({super.key, this.targetDate});

  @override
  _ReadPromiseState createState() => _ReadPromiseState();
}

class _ReadPromiseState extends State<ReadPromise> {
  // 替换原来的now变量
  late final DateTime now = widget.targetDate ?? DateTime.now();
  // 剩余代码保持不变
}

3. 配置数据库索引提升查询性能 #

当数据量较大时，为了避免查询报错、提升查询效率，需要在Firebase实时数据库的规则中为date字段配置索引：

{
  "rules": {
    "Daily Verse": {
      ".indexOn": "date",
      // 剩余原有规则保持不变
    }
  }
}

注意事项 #

• 必须保证DateFormat的输出格式和数据库中date字段的存储格式完全一致，包括月份拼写、大小写、空格、日期位数等，否则会出现匹配不到数据的问题
• 原代码中存在语法错误：build方法结束后多了一个多余的闭合大括号，需要删除避免编译报错

修改后完整代码 #

import 'package:firebase_database/firebase_database.dart';
import 'package:firebase_database/ui/firebase_animated_list.dart';
import 'package:flutter/material.dart';
import 'package:intl/intl.dart';

class ReadPromise extends StatefulWidget {
  final DateTime? targetDate;
  const ReadPromise({super.key, this.targetDate});

  @override
  _ReadPromiseState createState() => _ReadPromiseState();
}

class _ReadPromiseState extends State<ReadPromise> {
  late Query _ref;
  DatabaseReference reference =
  FirebaseDatabase.instance.reference().child('Daily Verse');
  late final DateTime now = widget.targetDate ?? DateTime.now();
  final DateFormat formatter = DateFormat("dd MMMM yyyy");

  @override
  void initState() {
    super.initState();
    String today = formatter.format(now);
    _ref = FirebaseDatabase.instance
        .reference()
        .child('Daily Verse')
        .orderByChild('date')
        .equalTo(today);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.indigo[900],
        title: const Text('Daily Promise Archive', textAlign: TextAlign.center,),
      ),
      body:Container(
        height: double.infinity,
        child: FirebaseAnimatedList(
           query: _ref,
          itemBuilder: (BuildContext context, DataSnapshot snapshot,
              Animation<double> animation, int index) {
              Map readVerse = snapshot.value as Map;
              readVerse['key'] = snapshot.key;
               return _buildContactItem(readPromise: readVerse);
              })
    )
    );
  }

  Widget _buildContactItem({required Map readPromise}) {
       return Container(
          margin: const EdgeInsets.symmetric(vertical: 10),
          padding: const EdgeInsets.all(10),
          height: 130,
          color: Colors.white,
          child: Container(
              child: Card(
                  color: Colors.indigo,
                  shadowColor: Colors.black,
                  child: Column(
                      mainAxisAlignment: MainAxisAlignment.center,
                      crossAxisAlignment: CrossAxisAlignment.start,
                      children: [
                        Row(
                          children: const [
                            SizedBox(
                              width: 6,
                            ),
                            Text(
                              '内容',
                              style: TextStyle(
                                  fontSize: 16,
                                  color: Colors.white,
                                  fontWeight: FontWeight.bold),
                            ),
                          ],
                        ),
                        const SizedBox(
                          height: 20,
                        ),
                        Row(
                          children: [
                            const SizedBox(
                              width: 6,
                            ),
                            Text(
                              readPromise['verse'],
                              style: const TextStyle(
                                  fontSize: 16,
                                  color: Colors.white,
                                  fontWeight: FontWeight.bold),
                            ),
                            const SizedBox(
                              width: 140,
                            ),
                            Text(
                              readPromise['date'],
                              style: const TextStyle(
                                  fontSize: 16,
                                  color: Colors.white,
                                  fontWeight: FontWeight.bold),
                            ),
                          ],
                        )
                      ]
                  )
              )));
  }
}

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