[Bug]: DateTime & TimeZone, invalid date returned

[tanukijs]

What happened?

Since i migrated to Realm, i saw a problem with my dates everywhere. It seems that all the date have been shifted to another TimeZone.

My phone has TimeZone set to Paris, it's 07:30 AM and realm return me 05:30 AM.

I found out that i can convert the date .toUtc() before inserting it to realm & convert it back to .toLocal() but as i didn't see any informations anywhere else than #569 i didn't expect DateTime field to work like that.

Repro steps

1. Define an entity that contain a DateTime field
2. Insert an entity with a DateTime
3. Compare the value of DateTime.now() & the value returned by our newly created entity

Version

3.3.0

What Realm SDK flavor are you using?

Local Database only

What type of application is this?

Flutter Application

Client OS and version

Realm Dart 0.4.0+beta

Code snippets

Here is a snippet, we only need an entity with a DateTime field to reproduce the problem.

final createdAt = DateTime.now(); // 07:30 AM
realm.write(() {
  entity.createdAt = createdAt;
  print('1 ${message.createdAt}');  // 05:30 AM
  print('2 $createdAt'); // 07:30 AM
});

Stacktrace of the exception/crash you're getting

No response

Relevant log output

[+16808 ms] flutter: 1 2022-09-14 05:51:00.831907Z
[   +1 ms] flutter: 2 2022-09-14 07:51:00.831907

[blagoev]

Hi,
DateTimes are persisted as UTC DateTimes in Realm. You need to convert it back to what timezone you need or the timezone of the device when you read the values.

[desistefanova]

Hi @tanukijs,
thanks for noticing this!
We will check the documentation.

[nielsenko]

Here is an example of how you can handle timezone data:

import 'package:realm_dart/realm.dart';
import 'package:timezone/timezone.dart' as tz;
import 'package:timezone/data/latest.dart' as tz;

part 'realm_datetime_with_timezone.g.dart';

@RealmModel()
class _Data {
  late DateTime dateTimeUtc;
  late String locationName; // tz database/Olson name

  tz.TZDateTime get dateTime => tz.TZDateTime.from(
        dateTimeUtc,
        tz.getLocation(locationName),
      );
}

Data createData(tz.TZDateTime value) => Data(
      DateTime.fromMillisecondsSinceEpoch(value.millisecondsSinceEpoch), // value.toUtc() won't work
      value.location.name,
    );

void main(List<String> arguments) {
  tz.initializeTimeZones();

  final paris = tz.getLocation('Europe/Paris');
  var year = 1789;

  final r = Realm(Configuration.inMemory([Data.schema]));
  r.write(() {
    while (year < 2023) {
      final bastilleDay = tz.TZDateTime(paris, year++, 7, 14);
      r.add(createData(bastilleDay));
    }
  });

  for (final data in r.all<Data>()) {
    final x = data.dateTime;
    print(
      'iso6801: ${x.toIso8601String()}, '
      'weekday: ${x.weekday}, ' // 1 based, ie. 1 is monday
      'location: ${x.location}, '
      'timezone: ${x.timeZone}, '
      'timezoneOffset: ${x.timeZoneOffset}',
    );
  }

  Realm.shutdown();
}

[desistefanova]

Hi @tanukijs,
We will add a note to our documentation about storing dates in UTC.
This issue will be resolved once the documentation is ready.
Thank you for your contribution!

[tanukijs]

Hello, this is way clearer to me. Thank you for your fast replies !
Edit: I let you manage the closing of the issue

[desistefanova]

Hi @tanukijs ,
Here is the section of the updated document in relation to storing UTC DateTame to Realm.
https://www.mongodb.com/docs/realm/sdk/flutter/realm-database/data-types/#datetime
Thanks! I'm closing the issue.

[sync-by-unito]

➤ Desislava Stefanova commented:

Updated documentation.