How to handle the result/s of Supabase queries in Flutter

Question

Related to my previous posting here about Flutter and Supabase, how can I handle the results of my queries using Supabase? It is not clear in the Supabase documentation about handling the returned results including error checking. I need a code snippet of the querying and handling the result/storing it in a variable/class. In my code, I am trying to check the credentials of a respondent logging in. I have tried to use Microsoft Bing/Copilot/ChatGPT, but it showed deprecated solutions, like queries with a .execute() and some response.data. My incomplete code snippet:

ElevatedButton(
   onPressed: () async {
      final supabase = Supabase.instance.client;
      final response = await supabase
              .from('respondents')
              .select()
              .eq('household_number', _householdNumberController.text)
              .eq('pin_password', _pinPasswordController.text)
              .maybeSingle();

              // Need to overhaul this part
              print(response);
              if (response != null) {
                 print('Ok');
              } else {
                      print('Not ok');
              }
             //
           },
   child: const Text('Login'),
),

If the result is just one entry, I need to save the details and pass/redirect to a new page, let's say SurveyForm. I also need to handle if the result is null or have multiple entries, since both will generate an error message.

The answers I have seen have used the Supabase auth. As I have mentioned in my previous posting, I need a different authentication method, which is just a simple check if a query will return something. Unfortunately, I have not seen a sample code yet or have not been using the right words to query it in the web.

[Update] This is the code snippet Microsoft Bing/ChatGPT answered but it does not work since .execute() is deprecated and response.data is not existing anymore. I need an updated version of this code.

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

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: LoginPage(),
    );
  }
}

class LoginPage extends StatefulWidget {
  @override
  _LoginPageState createState() => _LoginPageState();
}

class _LoginPageState extends State<LoginPage> {
  final _householdNumberController = TextEditingController();
  final _pinController = TextEditingController();

  Future<void> _login() async {
    final householdNumber = _householdNumberController.text;
    final pin = _pinController.text;

    final client = SupabaseClient('supabaseUrl', 'supabaseKey');

    final response = await client
        .from('Respondents')
        .select()
        .eq('household_number', householdNumber)
        .eq('pin', pin)
        .execute();

    if (response.data != null && response.data.isNotEmpty) {
      Navigator.push(
        context,
        MaterialPageRoute(builder: (context) => SurveyForm()),
      );
    } else {
      // Handle login failure...
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Column(
          children: <Widget>[
            TextField(
              controller: _householdNumberController,
              decoration: InputDecoration(labelText: 'Household Number'),
            ),
            TextField(
              controller: _pinController,
              decoration: InputDecoration(labelText: 'PIN'),
            ),
            ElevatedButton(
              onPressed: _login,
              child: Text('Login'),
            ),
          ],
        ),
      ),
    );
  }
}

class SurveyForm extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Build your survey form here...
    return Scaffold(
      body: Center(
        child: Text('Survey Form'),
      ),
    );
  }
}

Answer 1

You can get the count for this data using the following way -

To get the count of users

this.supabase.from('respondents').select('count', { count: 'exact' });

Then you can get a number of respondents fulfilling your requirements.

Let me give you a simple example: -

var users = await supabase.from('user_table').select();  //You will get an array here.
var isAuthenticated = users.length > 0 && users.length <=1; // Here true will conclude that the user is single and authenticated.


//And to find multiple users info is the following question.
for (var i = 0; i < users.length; i++) {
  print("Name : " + users[i]['name']);
  print("Last name : " + users[i]['lastName']);
}