get() returns incorrect results on iOS compared to Android or Web

[SoftWyer]

[REQUIRED] Step 1: Describe your environment

• Xcode version: 13.4.1
• Firebase SDK version: (not sure, pulled in by Flutter firebase_database 9.0.18)
• Installation method: CocoaPods
• Firebase Component: Database
• Target platform(s): iOS

[REQUIRED] Step 2: Describe the problem

Note that this is a copy of a bug originally raised in flutterfire firebase_database and is also described on SO here. It has been suggested to raise this bug here for tracking and visibility purposes.

When querying the database with a reference that contains four children, the data returned under iOS returns a snapshot from the first three children, not the fourth (e.g. from the reference's parent). The same code works correctly on Android and the Web.

Replacing get() for once() returns the correct data without any changes to the database reference.

Steps to reproduce:

The following code works correctly on Android and Web platforms:

  final DatabaseReference ref = FirebaseDatabase.instance.ref();
  
  // Get a reference, e.g. "items/-KbRRDWfIKVKPonCNV3-/-Lv4f4B-Of6qtbMB_21M/-LO9Rmgg6qadElqZW_U2"
  final getRef = ref.child('items').child(i.collectionUid!).child(i.parentUid!).child(i.uid);
 
  // Retrieve the data using get()
  final DataSnapshot snapshot = await getRef.get();

  // snapshot.value contains correct data on Android and Web, but is incorrect on iOS

On iOS, snapshot.value contains the data from the last but one child.

If the above code is changed to use once() in place of get(), then it works on all platforms, e.g.

  final DatabaseReference ref = FirebaseDatabase.instance.ref();
  
  // Get a reference, e.g. "items/-KbRRDWfIKVKPonCNV3-/-Lv4f4B-Of6qtbMB_21M/-LO9Rmgg6qadElqZW_U2"
  final getRef = ref.child('items').child(i.collectionUid!).child(i.parentUid!).child(i.uid);
 
  // Retrieve the data using once()
  final DataSnapshot snapshot = (await getRef.once()).snapshot;

  // snapshot.value contains correct data on all platforms

Futhermore there are some strange behaviours observed with the get queries

• putting additional children (with non-existent data paths) onto the reference still returns data from the third child when using get() whereas it should fail to find any data.
• this appears to be time dependent which may indicate cache or data corruption issues. Making the query at the very start of the application returns the correct results, but later on, after the application has loaded other data, it begins to return incorrect results.

Relevant Code:

(see above)

---

Flutter doctor

Flutter doctor

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 3.0.4, on macOS 12.4 21F79 darwin-x64, locale en-GB)
[✗] Android toolchain - develop for Android devices
    ✗ Unable to locate Android SDK.
      Install Android Studio from: https://developer.android.com/studio/index.html
      On first launch it will assist you in installing the Android SDK components.
      (or visit https://flutter.dev/docs/get-started/install/macos#android-setup for detailed instructions).
      If the Android SDK has been installed to a custom location, please use
      `flutter config --android-sdk` to update to that location.

[✓] Xcode - develop for iOS and macOS (Xcode 13.4.1)
[✓] Chrome - develop for the web
[!] Android Studio (not installed)
[✓] VS Code (version 1.69.0)
[✓] VS Code (version 1.51.1)
[✓] Connected device (4 available)
[✓] HTTP Host Availability

! Doctor found issues in 2 categories.

---

Flutter dependencies

Flutter dependencies

Dart SDK 2.17.5
Flutter SDK 3.0.4
collections 2.4.2+200

dependencies:
- archive 3.3.0 [crypto path]
- async 2.8.2 [collection meta]
- badges 2.0.3 [flutter]
- cached_network_image 3.2.1 [flutter flutter_cache_manager octo_image cached_network_image_platform_interface cached_network_image_web]
- charcode 1.3.1
- cloud_firestore 3.2.1 [cloud_firestore_platform_interface cloud_firestore_web collection firebase_core firebase_core_platform_interface flutter meta]
- collection 1.16.0
- connectivity 3.0.6 [flutter meta connectivity_platform_interface connectivity_macos connectivity_for_web]
- csv 5.0.1
- dynamic_theme 2.0.0 [flutter shared_preferences]
- email_validator 2.0.1
- file_picker 4.6.1 [flutter flutter_web_plugins flutter_plugin_android_lifecycle plugin_platform_interface ffi path win32]
- firebase_auth 3.4.1 [firebase_auth_platform_interface firebase_auth_web firebase_core firebase_core_platform_interface flutter meta]
- firebase_core 1.19.1 [firebase_core_platform_interface firebase_core_web flutter meta]
- firebase_crashlytics 2.8.4 [firebase_core firebase_core_platform_interface firebase_crashlytics_platform_interface flutter stack_trace]
- firebase_database 9.0.18 [firebase_core firebase_core_platform_interface firebase_database_platform_interface firebase_database_web flutter]
- firebase_storage 10.3.1 [firebase_core firebase_core_platform_interface firebase_storage_platform_interface firebase_storage_web flutter]
- firebase_ui 1.0.10 [flutter_localizations crypto device_info firebase_auth google_sign_in http sn_progress_dialog sign_in_with_apple]
- flutter 0.0.0 [characters collection material_color_utilities meta vector_math sky_engine]
- flutter_colorpicker 1.0.3 [flutter]
- flutter_html 2.2.1 [html csslib flutter_layout_grid video_player chewie webview_flutter chewie_audio flutter_svg flutter_math_fork collection numerus flutter]
- flutter_localizations 0.0.0 [flutter intl characters clock collection material_color_utilities meta path vector_math]
- flutter_markdown 0.6.10+2 [flutter markdown meta path]
- flutter_speed_dial 6.0.0 [flutter]
- flutter_svg 1.1.1+1 [flutter meta path_drawing vector_math xml]
- google_mobile_ads 1.3.0 [meta flutter]
- hive 2.2.3 [meta crypto]
- hive_flutter 1.1.0 [flutter hive path_provider path]
- html 0.15.0 [csslib source_span]
- i18n_extension 5.0.0 [sprintf args analyzer gettext_parser equatable intl flutter]
- image 3.2.0 [archive meta xml]
- image_cropper 2.0.3 [flutter image_cropper_platform_interface image_cropper_for_web]
- image_picker 0.8.5+3 [flutter image_picker_android image_picker_for_web image_picker_ios image_picker_platform_interface]
- in_app_purchase 3.0.6 [flutter in_app_purchase_android in_app_purchase_platform_interface in_app_purchase_storekit]
- in_app_purchase_android 0.2.3 [collection flutter in_app_purchase_platform_interface json_annotation]
- intl 0.17.0 [clock path]
- json_annotation 4.6.0 [meta]
- markdown 5.0.0 [args charcode meta]
- package_info_plus 1.4.2 [flutter package_info_plus_platform_interface package_info_plus_linux package_info_plus_macos package_info_plus_windows package_info_plus_web]
- path 1.8.1
- path_provider 2.0.11 [flutter path_provider_android path_provider_ios path_provider_linux path_provider_macos path_provider_platform_interface path_provider_windows]
- pdf 3.8.1 [archive barcode crypto image meta path_parsing vector_math xml]
- permission_handler 10.0.0 [flutter meta permission_handler_android permission_handler_apple permission_handler_windows permission_handler_platform_interface]
- photo_view 0.14.0 [flutter]
- printing 5.9.1 [ffi flutter flutter_web_plugins http image js meta pdf plugin_platform_interface]
- provider 6.0.3 [collection flutter nested]
- providerscope 1.0.2 [flutter flutter_image]
- qr_mobile_vision 3.0.1 [flutter native_device_orientation]
- rxdart 0.27.4
- scrollable_positioned_list 0.3.2 [flutter collection]
- share 2.0.4 [meta mime flutter]
- shared_preferences 2.0.15 [flutter shared_preferences_android shared_preferences_ios shared_preferences_linux shared_preferences_macos shared_preferences_platform_interface shared_preferences_web shared_preferences_windows]
- sliver_tools 0.2.7 [flutter]
- sn_progress_dialog 1.0.8 [flutter]
- sprintf 6.0.0
- timeago 3.2.2
- url_launcher 6.1.4 [flutter url_launcher_android url_launcher_ios url_launcher_linux url_launcher_macos url_launcher_platform_interface url_launcher_web url_launcher_windows]

dev dependencies:
- build_runner 2.1.11 [args async analyzer build build_config build_daemon build_resolvers build_runner_core code_builder collection crypto dart_style frontend_server_client glob graphs http_multi_server io js logging meta mime package_config path pool pub_semver pubspec_parse shelf shelf_web_socket stack_trace stream_transform timing watcher web_socket_channel yaml]
- flutter_test 0.0.0 [flutter test_api path fake_async clock stack_trace vector_math async boolean_selector characters charcode collection matcher material_color_utilities meta source_span stream_channel string_scanner term_glyph]
- hive_generator 1.1.3 [build source_gen hive analyzer source_helper]
- json_serializable 6.3.1 [analyzer async build build_config collection json_annotation meta path pub_semver pubspec_parse source_gen source_helper]
- lint 1.8.2

dependency overrides:
- flutter_svg 1.1.1+1 [flutter meta path_drawing vector_math xml]

transitive dependencies:
- _fe_analyzer_shared 38.0.0 [meta]
- analyzer 3.4.1 [_fe_analyzer_shared collection convert crypto glob meta package_config path pub_semver source_span watcher yaml]
- args 2.3.1
- barcode 2.2.1 [meta qr]
- boolean_selector 2.1.0 [source_span string_scanner]
- build 2.3.0 [analyzer async convert crypto glob logging meta path]
- build_config 1.0.0 [checked_yaml json_annotation path pubspec_parse yaml]
- build_daemon 3.1.0 [built_collection built_value http_multi_server logging path pool shelf shelf_web_socket stream_transform watcher web_socket_channel]
- build_resolvers 2.0.9 [analyzer async build crypto graphs logging path package_config pool pub_semver stream_transform yaml]
- build_runner_core 7.2.3 [async build build_config build_resolvers collection convert crypto glob graphs json_annotation logging meta path package_config pool timing watcher yaml]
- built_collection 5.1.1
- built_value 8.3.3 [built_collection collection fixnum meta]
- cached_network_image_platform_interface 1.0.0 [flutter flutter_cache_manager]
- cached_network_image_web 1.0.1 [flutter flutter_cache_manager cached_network_image_platform_interface]
- characters 1.2.0
- checked_yaml 2.0.1 [json_annotation source_span yaml]
- chewie 1.3.4 [cupertino_icons flutter provider video_player wakelock]
- chewie_audio 1.3.0 [cupertino_icons flutter video_player]
- clock 1.1.0
- cloud_firestore_platform_interface 5.5.10 [collection firebase_core flutter meta plugin_platform_interface]
- cloud_firestore_web 2.6.19 [cloud_firestore_platform_interface collection firebase_core firebase_core_web flutter flutter_web_plugins js]
- code_builder 4.1.0 [built_collection built_value collection matcher meta]
- connectivity_for_web 0.4.0+1 [connectivity_platform_interface flutter_web_plugins flutter]
- connectivity_macos 0.2.1+2 [flutter connectivity_platform_interface]
- connectivity_platform_interface 2.0.1 [flutter meta plugin_platform_interface]
- convert 3.0.2 [typed_data]
- cross_file 0.3.3+1 [js meta]
- crypto 3.0.2 [typed_data]
- csslib 0.17.2 [source_span]
- cupertino_icons 1.0.5
- dart_style 2.2.3 [analyzer args path pub_semver source_span]
- device_info 2.0.3 [flutter device_info_platform_interface]
- device_info_platform_interface 2.0.1 [flutter meta plugin_platform_interface]
- equatable 2.0.3 [collection meta]
- fake_async 1.3.0 [clock collection]
- ffi 1.2.1
- file 6.1.2 [meta path]
- firebase_auth_platform_interface 6.3.1 [firebase_core flutter meta plugin_platform_interface]
- firebase_auth_web 3.3.19 [firebase_auth_platform_interface firebase_core firebase_core_web flutter flutter_web_plugins http_parser intl js meta]
- firebase_core_platform_interface 4.4.3 [collection flutter flutter_test meta plugin_platform_interface]
- firebase_core_web 1.6.6 [firebase_core_platform_interface flutter flutter_web_plugins js meta]
- firebase_crashlytics_platform_interface 3.2.10 [collection firebase_core flutter meta plugin_platform_interface]
- firebase_database_platform_interface 0.2.1+10 [collection firebase_core flutter meta plugin_platform_interface]
- firebase_database_web 0.2.0+17 [firebase_core firebase_core_web firebase_database_platform_interface flutter flutter_web_plugins js]
- firebase_storage_platform_interface 4.1.10 [collection firebase_core flutter meta plugin_platform_interface]
- firebase_storage_web 3.2.19 [async firebase_core firebase_core_web firebase_storage_platform_interface flutter flutter_web_plugins http js meta]
- fixnum 1.0.1
- flutter_blurhash 0.7.0 [flutter]
- flutter_cache_manager 3.3.0 [clock collection file flutter http path path_provider pedantic rxdart sqflite uuid]
- flutter_image 1.0.0 [flutter]
- flutter_layout_grid 1.0.6 [flutter collection meta quiver]
- flutter_math_fork 0.6.3+1 [flutter flutter_svg provider meta collection tuple]
- flutter_plugin_android_lifecycle 2.0.6 [flutter]
- flutter_web_plugins 0.0.0 [flutter js characters collection material_color_utilities meta vector_math]
- frontend_server_client 2.1.3 [async path]
- gettext_parser 0.2.0
- glob 2.1.0 [async collection file path string_scanner]
- google_sign_in 5.4.0 [flutter google_sign_in_android google_sign_in_ios google_sign_in_platform_interface google_sign_in_web]
- google_sign_in_android 6.0.1 [flutter google_sign_in_platform_interface]
- google_sign_in_ios 5.4.0 [flutter google_sign_in_platform_interface]
- google_sign_in_platform_interface 2.2.0 [flutter quiver]
- google_sign_in_web 0.10.2 [flutter flutter_web_plugins google_sign_in_platform_interface js]
- graphs 2.1.0 [collection]
- http 0.13.4 [async http_parser meta path]
- http_multi_server 3.2.1 [async]
- http_parser 4.0.1 [collection source_span string_scanner typed_data]
- image_cropper_for_web 0.0.4 [flutter flutter_web_plugins image_cropper_platform_interface js]
- image_cropper_platform_interface 2.0.0 [flutter plugin_platform_interface http]
- image_picker_android 0.8.5+1 [flutter flutter_plugin_android_lifecycle image_picker_platform_interface]
- image_picker_for_web 2.1.8 [flutter flutter_web_plugins image_picker_platform_interface]
- image_picker_ios 0.8.5+6 [flutter image_picker_platform_interface]
- image_picker_platform_interface 2.5.0 [cross_file flutter http plugin_platform_interface]
- in_app_purchase_platform_interface 1.3.1 [flutter plugin_platform_interface]
- in_app_purchase_storekit 0.3.1 [collection flutter in_app_purchase_platform_interface json_annotation]
- io 1.0.3 [meta path string_scanner]
- js 0.6.4
- logging 1.0.2
- matcher 0.12.11 [stack_trace]
- material_color_utilities 0.1.4
- meta 1.7.0
- mime 1.0.2
- native_device_orientation 1.1.4 [flutter meta]
- nested 1.0.0 [flutter]
- numerus 1.1.1
- octo_image 1.0.2 [flutter flutter_blurhash]
- package_config 2.1.0 [path]
- package_info_plus_linux 1.0.5 [package_info_plus_platform_interface flutter path]
- package_info_plus_macos 1.3.0 [flutter]
- package_info_plus_platform_interface 1.0.2 [flutter meta plugin_platform_interface]
- package_info_plus_web 1.0.5 [flutter flutter_web_plugins http meta package_info_plus_platform_interface]
- package_info_plus_windows 1.0.5 [package_info_plus_platform_interface ffi flutter win32]
- path_drawing 1.0.0 [vector_math meta path_parsing flutter]
- path_parsing 1.0.0 [vector_math meta]
- path_provider_android 2.0.16 [flutter path_provider_platform_interface]
- path_provider_ios 2.0.10 [flutter path_provider_platform_interface]
- path_provider_linux 2.1.7 [ffi flutter path path_provider_platform_interface xdg_directories]
- path_provider_macos 2.0.6 [flutter path_provider_platform_interface]
- path_provider_platform_interface 2.0.4 [flutter platform plugin_platform_interface]
- path_provider_windows 2.0.7 [ffi flutter path path_provider_platform_interface win32]
- pedantic 1.11.1
- permission_handler_android 10.0.0 [flutter permission_handler_platform_interface]
- permission_handler_apple 9.0.4 [flutter permission_handler_platform_interface]
- permission_handler_platform_interface 3.7.0 [flutter meta plugin_platform_interface]
- permission_handler_windows 0.1.0 [flutter permission_handler_platform_interface]
- petitparser 5.0.0 [meta]
- platform 3.1.0
- plugin_platform_interface 2.1.2 [meta]
- pool 1.5.1 [async stack_trace]
- process 4.2.4 [file path platform]
- pub_semver 2.1.1 [collection meta]
- pubspec_parse 1.2.0 [checked_yaml collection json_annotation pub_semver yaml]
- qr 3.0.1 [meta]
- quiver 3.1.0 [matcher]
- shared_preferences_android 2.0.12 [flutter shared_preferences_platform_interface]
- shared_preferences_ios 2.1.1 [flutter shared_preferences_platform_interface]
- shared_preferences_linux 2.1.1 [file flutter path path_provider_linux path_provider_platform_interface shared_preferences_platform_interface]
- shared_preferences_macos 2.0.4 [flutter shared_preferences_platform_interface]
- shared_preferences_platform_interface 2.0.0 [flutter]
- shared_preferences_web 2.0.4 [flutter flutter_web_plugins shared_preferences_platform_interface]
- shared_preferences_windows 2.1.1 [file flutter path path_provider_platform_interface path_provider_windows shared_preferences_platform_interface]
- shelf 1.3.1 [async collection http_parser path stack_trace stream_channel]
- shelf_web_socket 1.0.2 [shelf stream_channel web_socket_channel]
- sign_in_with_apple 3.3.0 [flutter meta sign_in_with_apple_platform_interface sign_in_with_apple_web]
- sign_in_with_apple_platform_interface 1.0.0 [flutter plugin_platform_interface meta]
- sign_in_with_apple_web 1.0.1 [flutter flutter_web_plugins sign_in_with_apple_platform_interface js]
- sky_engine 0.0.99
- source_gen 1.2.2 [analyzer async build dart_style glob meta path source_span yaml]
- source_helper 1.3.2 [analyzer collection source_gen]
- source_span 1.8.2 [collection path term_glyph]
- sqflite 2.0.3 [flutter sqflite_common path]
- sqflite_common 2.2.1+1 [synchronized path meta]
- stack_trace 1.10.0 [path]
- stream_channel 2.1.0 [async]
- stream_transform 2.0.0
- string_scanner 1.1.0 [charcode source_span]
- synchronized 3.0.0+2
- term_glyph 1.2.0
- test_api 0.4.9 [async boolean_selector collection meta source_span stack_trace stream_channel string_scanner term_glyph matcher]
- timing 1.0.0 [json_annotation]
- tuple 2.0.0 [quiver]
- typed_data 1.3.1 [collection]
- url_launcher_android 6.0.17 [flutter url_launcher_platform_interface]
- url_launcher_ios 6.0.17 [flutter url_launcher_platform_interface]
- url_launcher_linux 3.0.1 [flutter url_launcher_platform_interface]
- url_launcher_macos 3.0.1 [flutter url_launcher_platform_interface]
- url_launcher_platform_interface 2.1.0 [flutter plugin_platform_interface]
- url_launcher_web 2.0.12 [flutter flutter_web_plugins url_launcher_platform_interface]
- url_launcher_windows 3.0.1 [flutter url_launcher_platform_interface]
- uuid 3.0.6 [crypto]
- vector_math 2.1.2
- video_player 2.4.5 [flutter html video_player_android video_player_avfoundation video_player_platform_interface video_player_web]
- video_player_android 2.3.6 [flutter video_player_platform_interface]
- video_player_avfoundation 2.3.5 [flutter video_player_platform_interface]
- video_player_platform_interface 5.1.3 [flutter plugin_platform_interface]
- video_player_web 2.0.10 [flutter flutter_web_plugins video_player_platform_interface]
- wakelock 0.6.2 [flutter meta wakelock_macos wakelock_platform_interface wakelock_web wakelock_windows]
- wakelock_macos 0.4.0 [flutter flutter_web_plugins wakelock_platform_interface]
- wakelock_platform_interface 0.3.0 [flutter meta]
- wakelock_web 0.4.0 [flutter flutter_web_plugins js wakelock_platform_interface]
- wakelock_windows 0.2.0 [flutter wakelock_platform_interface win32]
- watcher 1.0.1 [async path]
- web_socket_channel 2.2.0 [async crypto stream_channel]
- webview_flutter 2.8.0 [flutter webview_flutter_android webview_flutter_platform_interface webview_flutter_wkwebview]
- webview_flutter_android 2.8.14 [flutter webview_flutter_platform_interface]
- webview_flutter_platform_interface 1.9.1 [flutter meta plugin_platform_interface]
- webview_flutter_wkwebview 2.8.1 [flutter path webview_flutter_platform_interface]
- win32 2.6.1 [ffi]
- xdg_directories 0.2.0+1 [meta path process]
- xml 6.1.0 [collection meta petitparser]
- yaml 3.1.1 [collection source_span string_scanner]

---

[paulb777]

We'll likely need a Swift or Objective C repro to help here. While there may be a bug in the native SDK, there could also be a bug in the flutter binding. Otherwise, I'd recommend reopening the flutter issue.

[SoftWyer]

@paulb777 appreciate the problem with being able to identify the underlying cause and narrowing it done to specific components. I'm not able to easily create a test case beyond the Flutter code I work with as I'm unfamiliar with iOS/XCode/Swift in any context other than Flutter builds.

If there's a straightforward example the team here has of using the ios-sdk that uses the same underlying code that the Flutter get call uses, please point me at it and I'll see if I can hook it into my firebase instance and try and replicate the issue.

I'm happy for the Flutter issue to be reopened, but that decision needs to come from both firebase teams, rather than have me bouncing around teams :-)

[paulb777]

@SoftWyer Sorry about the bounce. I reopened firebase/flutterfire#9067