如何使用 Flutter 从 Firestore 中的 collectionGroups 查询数据

Question

For an app I'm building in Flutter I'm trying to retrieve a list of reserved timeslots by the logged in user across different days from Firestore. I get to a point where I can retrieve the reserved timeslots on a given day (by hardcoding the day and passing it on to a futurebuilder), but when I try to retrieve data from a collectionGroup the listview stays empty (snapshot doesn't have data). Now, as a Flutter beginner I find understanding how to handle collectionGroup queries quite difficult and therefore any help would be appreciated!

For a quick overview of how my database is structured I have included 2 pictures on github:

Picture 1: https://github.com/winckles/rooster/blob/master/Schermafbeelding%202019-11-10%20om%2020.08.20.png?raw=true

Picture 2: https://github.com/winckles/rooster/blob/master/Schermafbeelding%202019-11-10%20om%2020.08.43.png?raw=true

Below I have included my futurebuilder and listview builder

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

class TimesTest extends StatefulWidget {
  @override
  _TimesTestState createState() => _TimesTestState();
}

class _TimesTestState extends State<TimesTest> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        child: MyFutureBuilder(),
      ),
    );
  }
}

class MyFutureBuilder extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: MyTimes().getMyTimes('${loggedInUser.email}'),
      builder: (context, AsyncSnapshot snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting) {
          return Center(
            child: CircularProgressIndicator(
              backgroundColor: Colors.lightBlueAccent,
            ),
          );
        } else if (snapshot.hasData) {
          return ListView.builder(
              padding: EdgeInsets.symmetric(horizontal: 10.0, vertical: 20.0),
              itemCount: snapshot.data.documents.length,
              itemBuilder: (BuildContext context, int index) {
                DocumentSnapshot user = snapshot.data.documents[index];
                return Padding(
                  padding: EdgeInsets.symmetric(
                    horizontal: 7.0,
                    vertical: 3.0,
                  ),
                  child: Column(
                    crossAxisAlignment: CrossAxisAlignment.start,
                    children: <Widget>[
                      Card(
                        color: Colors.white,
                        child: Container(
                          child: ListTile(
                            onTap: () {},
                            title: Text(
                              user.data['hour'],
                              style: TextStyle(
                                color: Colors.grey[900],
                              ),
                            ),
                            subtitle: Text(
                              user.data['reserved'],
                              style: TextStyle(
                                color: Colors.grey[900],
                              ),
                            ),
                            leading: Icon(
                              Icons.access_time,
                              color: Colors.grey[900],
                            ),
                          ),
                        ),
                      ),
                    ],
                  ),
                );
              });
        } else if (snapshot.connectionState == ConnectionState.done &&
            !snapshot.hasData) {
          return Center(
            child: Text('No times found'),
          );
        } else {
          return Center(
            child: Text('Something else is wrong'),
          );
        }
      },
    );
  }
}

And this is how I get the data from firestore.

import 'package:cloud_firestore/cloud_firestore.dart';

class MyTimes {
  Future getMyTimes(String reserved) async {
    return Firestore.instance
        .collectionGroup('hours')
        .where('reserved', isEqualTo: reserved)
        .getDocuments();
  }
}

I have created an index with collection id 'hours' and with collection range 'collectionGroup', my security rules right now are the following:

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write: if true;
    }

    match /{path=**}/hours/{document}{
    allow read, write;
    }
  }
}

I've spend hours and hours trying to find this out already, so really anything useful would greatly be appreciated!

Answer 1

I found the solution to my problem; First my snapshot could retrieve ALL the data from 'hours' When I removed the .where('reserved', isEqualTo: reserved) , but it didn't work when I included it, so the code worked but only the query didn't. This was due to the index settings of my Firestore database. I read the documentation on indexes for Firestore here: https://firebase.google.com/docs/firestore/query-data/index-overview?authuser=0#automatic_indexing

After I realized I had only made a composite index while I didn't look at the single-field index exemptions . I added two exemptions:

One for the field 'hour' in collectionGroup 'hours' while checking the boxes ascending and descending and one for the field 'reserved' in collectionGroup 'hours' while checking the boxes ascending and descending again. Now it does work!

Answer 2

After I realized I had only made a composite index while I didn't look at the single-field index exemptions

If you are looking for a way of doing this using firebase cli you can do it in this way:

1. create a file called firestore.indexes.json

{
  "indexes": [],
  "fieldOverrides": [
    {
      "collectionGroup": "your_sub_collection",
      "fieldPath": "the_field",
      "indexes": [
        {
          "order": "ASCENDING",
          "queryScope": "COLLECTION"
        },
        {
          "order": "DESCENDING",
          "queryScope": "COLLECTION"
        },
        {
          "arrayConfig": "CONTAINS",
          "queryScope": "COLLECTION"
        },
        {
          "order": "ASCENDING",
          "queryScope": "COLLECTION_GROUP"
        }
      ]
    }
  ]
}

In this way, you are preserving the default for the collection scope and enabling the ASCENDING one for the collection group scope instead.

1. In your firebase.json :

  "firestore": {
    "indexes": "indexes/firestore.indexes.json"
  },

3. run firebase deploy --only firestore:indexes

This will do the job and finally, your collectionGroup query will work as expected.

Hope it helps to save some time.

Answer 3

In your example, you are not using a collectionGroup query. You need to do something like Firestore.instance.collectionGroup('hours').where('reserved', isEqualTo: '').getDocuments(); for non-reserved slots.

So, what do you store in your 002 document when that slot ís reserved? And why don't you use an explicit type like a boolean for the status? That makes it easier too.