Musicbrainz genres deleted using `mbsync` after https://github.com/beetbox/beets/pull/6401

[aereaux]

Problem

Running this command in verbose (-vv) mode:

$ beet -vvv mbsync Copland
user configuration: /home/user/.config/beets/config.yaml
data directory: /home/user/.config/beets
plugin paths: ['/home/user/.config/beets/plugins']
Loading plugins: chroma, convert, edit, fetchart, fish, info, inline, listenbrainz, m3ufixer, mbcollection, mbsync, musicbrainz, parentwork, play, scrub, smartplaylist
/home/user/.local/share/uv/tools/beets/lib/python3.14/site-packages/requests/__init__.py:113: RequestsDependencyWarning: urllib3 (2.6.3) or chardet (6.0.0.post1)/charset_normalizer (3.4.4) doesn't match a supported version!
  warnings.warn(
inline: adding item field mpd_path
inline: adding album field mb_albumurl
fetchart: google: Disabling art source due to missing key
fetchart: lastfm: Disabling art source due to missing key
Sending event: pluginload
library database: /home/user/.config/beets/library.db
library directory: /home/user/music/beets
Sending event: library_opened
Parsed query: AndQuery([OrQuery([SubstringQuery('artist', 'Copland', fast=True), SubstringQuery('title', 'Copland', fast=True), SubstringQuery('comments', 'Copland', fast=True), SubstringQuery('album', 'Copland', fast=True), SubstringQuery('albumartist', 'Copland', fast=True), SubstringQuery('genres', 'Copland', fast=True)]), NoneQuery('album_id', True)])
Parsed sort: NullSort()
Parsed query: AndQuery([OrQuery([SubstringQuery('album', 'Copland', fast=True), SubstringQuery('albumartist', 'Copland', fast=True), SubstringQuery('genres', 'Copland', fast=True)])])
Parsed sort: NullSort()
musicbrainz: Requesting MusicBrainz release 192a76ff-b05a-4988-9f0a-bc095d44fcd3
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_album_extract
Sending event: albuminfo_received
mbsync: applying changes to Samuel Barber, Charles Ives, Aaron Copland; Academy of St Martin in the Fields, Sir Neville Marriner - Barber: Adagio for Strings / Ives: Symphony no. 3 / Copland: Quiet City
musicbrainz: Requesting MusicBrainz release a881c055-6d9a-4abb-8e5f-63107797e7d4
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_album_extract
Sending event: albuminfo_received
mbsync: applying changes to Béla Bartók, Leonard Bernstein, Aaron Copland, Morton Gould, Игорь Фёдорович Стравинский; Benny Goodman - Benny Goodman Collector's Edition: Compositions & Collaborations
Béla Bartók - Benny Goodman Collector's Edition: Compositions & Collaborations - Contrasts: I. Verbunkos (Recruiting Dance)
  genres:
    - classical
    - jazz
Parsed query: AndQuery([NoneQuery('album_id', True)])
Parsed sort: NullSort()
Parsed query: AndQuery([BooleanQuery('comp', 1, fast=True)])
Parsed sort: NullSort()
Sending event: before_item_moved
Sending event: item_moved
m3ufixer: Building m3u cache...
Sending event: database_change
Sending event: write
Sending event: after_write
Sending event: database_change
Béla Bartók - Benny Goodman Collector's Edition: Compositions & Collaborations - Contrasts: II. Pihenö (Relaxation)
  genres:
    - classical
    - jazz
[...]

Led to this problem:

The genres are being removed

Here's a link to the music files that trigger the bug (if relevant):

Setup

• OS: Arch Linux
• Python version: 3.14.3
• beets version: 573dca6
• Turning off plugins made problem go away (yes/no): N/A (needs musicbrainz plugin)

My configuration (output of beet config) is:

[...]
musicbrainz:
    genres: yes
[...]

It looks like the genres are still being received in the musicbrainz plugin, and being set in info.genres, but something might be happening after this.

[aereaux]

I tried to bisect, but there are some revisions that error:

/home/user/.local/share/uv/tools/beets/lib/python3.14/site-packages/requests/__init__.py:113: RequestsDependencyWarning: urllib3 (2.6.3) or chardet (6.0.0.post1)/charset_normalizer (3.4.4) doesn't match a supported version!
  warnings.warn(
Traceback (most recent call last):
  File "/home/user/.local/bin/beet", line 10, in <module>
    sys.exit(main())
             ~~~~^^
  File "/home/user/.local/lib/beets/beets/ui/__init__.py", line 1633, in main
    _raw_main(args)
    ~~~~~~~~~^^^^^^
  File "/home/user/.local/lib/beets/beets/ui/__init__.py", line 1608, in _raw_main
    subcommands, lib = _setup(options, lib)
                       ~~~~~~^^^^^^^^^^^^^^
  File "/home/user/.local/lib/beets/beets/ui/__init__.py", line 1445, in _setup
    lib = _open_library(config)
  File "/home/user/.local/lib/beets/beets/ui/__init__.py", line 1505, in _open_library
    lib = library.Library(
        dbpath,
    ...<2 lines>...
        get_replacements(),
    )
  File "/home/user/.local/lib/beets/beets/library/library.py", line 33, in __init__
    super().__init__(path, timeout=timeout)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/beets/beets/dbcore/db.py", line 1130, in __init__
    self._migrate()
    ~~~~~~~~~~~~~^^
  File "/home/user/.local/lib/beets/beets/dbcore/db.py", line 1348, in _migrate
    migration.migrate_table(model_cls._table)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/beets/beets/dbcore/db.py", line 1060, in migrate_table
    if not self.db.migration_exists(self.name, table):
           ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/home/user/.local/lib/beets/beets/dbcore/db.py", line 1353, in migration_exists
    return tx.execute(
           ^^^^^^^^^^
AttributeError: 'Transaction' object has no attribute 'execute'
$ git bisect skip
There are only 'skip'ped commits left to test.
The first bad commit could be any of:
4dda8e3e49489f0b1b6e83dbc9a35d9fbc85e0a4
cf36ed07546d78c27df6d1d4d57ebda0d1750be6
2ecbe59f48ddc07bc9ba31c8c16102442ef7870f
b8f1b9d174afb353b93e7ee3f04c31cb40fdd796
5d7fb4e1586c5fa5c4e79a6010dd65ca37e3c37b
We cannot bisect more!

[snejus]

I can reproduce, see

It seems like the behaviour is not limited to genres field only, mbsync also clears my album tags too.

[snejus]

Apologies regarding bisect - seems like I wasn't too careful regarding my commits and there are several broken commits where execute method was not present which I later removed.

[aereaux]

Yeah, I'm stumped here, I'm not sure what in the diff between the good and bad commits could be causing this. Could it be related to the dbcore changes?

[aereaux]

I did a bit more debugging, and it looks like with the old code it sets the genre field in the track info items in MBSyncPlugin.items(), but it doesn't with the new code. I'm not sure why that is though.

[snejus]

Seems like the plugin only applies track-level fields:

            track_index = defaultdict(list)
            print(album_info.genres)
            for track_info in album_info.tracks:
                print(track_info.genres)

$ beet mbsync data_source:brainz eminem
['hip hop', 'conscious hip hop', 'pop rap', 'hardcore hip hop', 'gangsta rap']
[]
[]
[]
57430 | 2002 / Lose Yourself: Eminem - Lose Yourself
  album: Lose Yourself -> 
  genres:
    - conscious hip hop
    - gangsta rap
    - hardcore hip hop
    - pop rap
    - rap rock

[snejus]

Actually, the issue is in _apply_metadata function which did not take into account empty multi-valued fields. The fix:

diff --git a/beets/autotag/__init__.py b/beets/autotag/__init__.py
index feeefbf28..e6be9d1a1 100644
--- a/beets/autotag/__init__.py
+++ b/beets/autotag/__init__.py
@@ -127,7 +127,7 @@ def _apply_metadata
 
         # Don't overwrite fields with empty values unless the
         # field is explicitly allowed to be overwritten.
-        if value is None and field not in nullable_fields:
+        if (value is None or value == []) and field not in nullable_fields:
             continue
 
         db_obj[field] = value

[snejus]

Now need to figure out where does the album field get lost

[snejus]

Ah, album was NULLed on my end because I had

overwrite_null:
  track:
    - album

in my configuration.

[djl]

This still seems to be happening for me:

$ bq ls -a -f '$album - $genres' tryra
Tryra - deep techno
$ bq -vvv mbsync -p tryra
user configuration: /home/djl/.config/beets/config.yaml
data directory: /home/djl/.config/beets
plugin paths: ['/home/djl/.config/beets/plugins']
Loading plugins: artwork, catalog, checkcredits, checkdirs, checkflacs, checkmpd, checkpaths, checks, convert, copyartifacts, downsampler, dupes, fetchart, findreplace, fuzzy, genres, headphones, importfeeds, info, inline, limit, mbcollections, mbopenurl, mborphans, mbsync, mbtpg, mbtrackutils, missing, missingfiles, missingreleases, musicbrainz, orphans, querystore, scrub, templateutils, timedelta, types, upgrades, wipe, zero
fetchart: google: Disabling art source due to missing key
fetchart: lastfm: Disabling art source due to missing key
genres: Skipping disabled fetcher: lastfm
inline: adding item field multidisc
inline: adding item field disc_unpadded
inline: adding item field disc_smartpadded
inline: adding item field added_simple
inline: adding album field bitrate
inline: adding album field bitdepth
inline: adding album field date
inline: adding album field all_formats
inline: adding album field all_media
inline: adding album field filesize
inline: adding album field mburl
inline: adding album field mbgurl
inline: adding album field disambigs
inline: adding album field years
inline: adding album field brlabel
Sending event: pluginload
library database: /home/djl/var/beets/library.db
library directory: /data/media/audio/music
Sending event: library_opened
Parsed query: AndQuery([OrQuery([SubstringQuery('artist', 'tryra', fast=True), SubstringQuery('title', 'tryra', fast=True), SubstringQuery('comments', 'tryra', fast=True), SubstringQuery('album', 'tryra', fast=True), SubstringQuery('albumartist', 'tryra', fast=True), SubstringQuery('genres', 'tryra', fast=True)]), NoneQuery('album_id', True)])
Parsed sort: NullSort()
Parsed query: AndQuery([OrQuery([SubstringQuery('album', 'tryra', fast=True), SubstringQuery('albumartist', 'tryra', fast=True), SubstringQuery('genres', 'tryra', fast=True)])])
Parsed sort: NullSort()
musicbrainz: Requesting MusicBrainz release 7121ed80-d6b6-4f85-baf8-6035dd334209
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_track_extract
Sending event: mb_album_extract
Sending event: albuminfo_received
mbsync: applying changes to Daniel[i] - Tryra
Sending event: album_matched
Daniel[i] - Tryra - Hegrei
  genres:
    - deep techno
Daniel[i] - Tryra - Prahi
  genres:
    - deep techno
Daniel[i] - Tryra - Sgyro
  genres:
    - deep techno
Daniel[i] - Tryra - Tryra
  genres:
    - deep techno
Sending event: cli_exit
Sending event: artifacts_copied

I'm definitely up to date with beets also:

prj/beets@master% git rev-parse HEAD
72b4c771612df3dbaee56c4460fe76297ddf9a87

[aereaux]

This still seems to be happening for me:

What is your config? And this happens with other albums in your library?