From 4417fea0abfe074b869c018933633c997f9e9bdd Mon Sep 17 00:00:00 2001
From: Vincent Gao <gaobing1230@gmail.com>
Date: Sat, 27 Jun 2026 10:52:09 +0200
Subject: [PATCH] Fix storing flex media fields during update

---
 beets/dbcore/db.py              |  2 +-
 docs/changelog.rst              |  2 ++
 test/test_dbcore.py             |  9 +++++++++
 test/ui/commands/test_update.py | 25 +++++++++++++++++++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/beets/dbcore/db.py b/beets/dbcore/db.py
index ca42eb2b10..517368abf5 100755
--- a/beets/dbcore/db.py
+++ b/beets/dbcore/db.py
@@ -599,7 +599,7 @@ def store(self, fields: Iterable[str] | None = None):
         assignments = []
         subvars: list[SQLiteType] = []
         for key in fields:
-            if key != "id" and key in self._dirty:
+            if key != "id" and key in self._fields and key in self._dirty:
                 self._dirty.remove(key)
                 assignments.append(f"{key}=?")
                 value = self._type(key).to_sql(self[key])
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 2609ce8fa9..caabfb249e 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -34,6 +34,8 @@ Bug fixes
   example a multi-disc album whose cover lives in the album root rather than a
   per-disc directory); the missing art is skipped instead. :bug:`4692`
 - :doc:`plugins/tidal`: Normalize Tidal album types to lowercase.
+- ``beet update`` no longer crashes when a plugin-added media field is stored as
+  a flexible attribute. :bug:`5580`
 
 ..
     For plugin developers
diff --git a/test/test_dbcore.py b/test/test_dbcore.py
index 283a3c6c2a..e8833b0e5f 100644
--- a/test/test_dbcore.py
+++ b/test/test_dbcore.py
@@ -325,6 +325,15 @@ def test_store_and_retrieve_flexattr(self):
         other_model = self.db._get(ModelFixture1, model.id)
         assert other_model.foo == "bar"
 
+    def test_store_flexattr_in_fields(self):
+        model = ModelFixture1()
+        model.add(self.db)
+        model.foo = "bar"
+        model.store(fields=["foo"])
+
+        other_model = self.db._get(ModelFixture1, model.id)
+        assert other_model.foo == "bar"
+
     def test_delete_flexattr(self):
         model = ModelFixture1()
         model["foo"] = "bar"
diff --git a/test/ui/commands/test_update.py b/test/ui/commands/test_update.py
index 937ded10cb..003ef71b9e 100644
--- a/test/ui/commands/test_update.py
+++ b/test/ui/commands/test_update.py
@@ -1,8 +1,10 @@
 import os
 
+import mediafile
 from mediafile import MediaFile
 
 from beets import library
+from beets.plugins import BeetsPlugin
 from beets.test import _common
 from beets.test.helper import BeetsTestCase, IOMixin
 from beets.ui.commands.update import update_items
@@ -84,6 +86,29 @@ def test_modified_metadata_detected(self):
         item = self.lib.items().get()
         assert item.title == "differentTitle"
 
+    def test_modified_plugin_media_field_detected(self):
+        plugin = BeetsPlugin()
+        plugin.add_media_field(
+            "customtag",
+            mediafile.MediaField(
+                mediafile.MP3DescStorageStyle("customtag"),
+                mediafile.StorageStyle("customtag"),
+            ),
+        )
+
+        try:
+            mf = MediaFile(syspath(self.i.path))
+            mf.customtag = "F#"
+            mf.save()
+
+            self._update()
+
+            item = self.lib.get_item(self.i.id)
+            assert item["customtag"] == "F#"
+        finally:
+            delattr(mediafile.MediaFile, "customtag")
+            library.Item._media_fields.remove("customtag")
+
     def test_modified_metadata_moved(self):
         mf = MediaFile(syspath(self.i.path))
         mf.title = "differentTitle"