From 1c64b8be32a6ba4db5cd3da33ec5f7aad5e67784 Mon Sep 17 00:00:00 2001
From: Maxr1998 <max.rumpf1998@gmail.com>
Date: Sat, 29 Mar 2025 13:07:41 +0100
Subject: [PATCH 1/3] Convert flexible field values to SQL before storing them

This is required to support multivalued fields as flexible fields.
---
 beets/dbcore/db.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/beets/dbcore/db.py b/beets/dbcore/db.py
index b780c5756..a569feba7 100755
--- a/beets/dbcore/db.py
+++ b/beets/dbcore/db.py
@@ -607,6 +607,7 @@ class Model(ABC, Generic[D]):
             for key, value in self._values_flex.items():
                 if key in self._dirty:
                     self._dirty.remove(key)
+                    value = self._type(key).to_sql(value)
                     tx.mutate(
                         "INSERT INTO {} "
                         "(entity_id, key, value) "

From 55ef006b3e6908d05a1c158550c7b273008e3ea8 Mon Sep 17 00:00:00 2001
From: Maxr1998 <max.rumpf1998@gmail.com>
Date: Sun, 29 Jun 2025 12:45:15 +0200
Subject: [PATCH 2/3] Add changelog entry

---
 docs/changelog.rst | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 7fb81237e..c2b0c0ca5 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -76,7 +76,11 @@ For plugin developers:
         ``album_for_id``, ``candidates``, ``item_candidates``, ``album_distance``, ``track_distance`` methods,
         please update your plugin to inherit from the new baseclass, as otherwise your plugin will
         stop working with the next major release.
-        
+* Flexible fields, which can be used by plugins to store additional metadata,
+  now also support list values. Previously, beets would throw an error while
+  storing the data in the SQL database due to missing type conversion.
+  :bug:`5698`
+
 Other changes:
 
 * Refactor: Split responsibilities of Plugins into MetaDataPlugins and general Plugins.

From 8db661b115044ccdd9ccb51c8662a8f7f8b1d513 Mon Sep 17 00:00:00 2001
From: Maxr1998 <max.rumpf1998@gmail.com>
Date: Wed, 16 Jul 2025 21:41:29 +0200
Subject: [PATCH 3/3] Add test

---
 test/test_plugins.py | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/test/test_plugins.py b/test/test_plugins.py
index 207522430..d9da17e61 100644
--- a/test/test_plugins.py
+++ b/test/test_plugins.py
@@ -94,6 +94,20 @@ class ItemTypesTest(PluginLoaderTestCase):
         out = self.run_with_output("ls", "rating:3..5")
         assert "aaa" not in out
 
+    def test_multi_value_flex_field_type(self):
+        class MultiValuePlugin(plugins.BeetsPlugin):
+            item_types = {"multi_value": types.MULTI_VALUE_DSV}
+
+        self.register_plugin(MultiValuePlugin)
+
+        item = Item(path="apath", artist="aaa")
+        item.multi_value = ["one", "two", "three"]
+        item.add(self.lib)
+
+        out = self.run_with_output("ls", "-f", "$multi_value")
+        delimiter = types.MULTI_VALUE_DSV.delimiter
+        assert out == f"one{delimiter}two{delimiter}three\n"
+
 
 class ItemWriteTest(PluginLoaderTestCase):
     def setUp(self):