Fix Model.store() crash when fields= contains a flexible attribute

[e4779]

Summary

Model.store(fields=...) filters the requested field set to fixed columns before building the main-table UPDATE, so a flexible attribute passed via fields= is routed through the existing _flex_table INSERT path instead of crashing.

Fixes #5580.

Root cause

A plugin can register the same field name two ways:

​```python
class FooPlugin(BeetsPlugin):
item_types = {"foo": types.Float()} # typed flex attribute

def __init__(self):
    super().__init__()
    self.add_media_field("foo", mediafile.MediaField(...))  # adds to Item._media_fields

​```

item_types keeps the field as a flexible attribute (no schema column). add_media_field adds the name to library.Item._media_fields. When beet update is called without --fields, update_items falls back to library.Item._media_fields, which now contains the flex attribute name. It is then forwarded to Model.store(fields=...), whose store loop built UPDATE <table> SET <flex_field>=? for every dirty field without checking whether the field had a real column. For flex attributes the column does not exist, so:

​ sqlite3.OperationalError: no such column: foo File ".../beets/dbcore/db.py", line 608, in store tx.mutate(query, subvars) ​

This matches the trace in #5580 (originally reported for beets 2.2.0; still reproducible on current master).

Fix

In Model.store(), partition the incoming fields:

​python column_fields = [f for f in fields if f in self._fields] ​

and use column_fields for the main-table UPDATE. Flexible attributes are already persisted just below via the _values_flex INSERT path, so they keep round-tripping correctly — no behaviour change for the common case (no plugin, or plugin that only uses item_types). The previous code already iterated self._values_flex separately, so the only missing piece was the filter.

The fields=None default path (fields = self._fields) is already all-columns, so it is unaffected.

How I validated

• Added a regression test in test/dbcore/test_db.py::ModelTest::test_store_with_flex_field_in_fields_argument that stores a typed flex attribute (some_float_field, declared in ModelFixture1._types) through store(fields=[...]) and asserts the value survives a fresh load. The test fails on master with OperationalError: no such column: some_float_field and passes with this change.
• Full test suite (poe test, deselecting the two known root-in-container / poe docs expected failures documented in the dev guide): 2572 passed, 156 skipped — one more than the clean-HEAD baseline of 2571 (the new test), with no regressions.
• poe lint, poe format, and poe check-types . all clean.

Why not roll back commit acff509 (the alternative proposed in the issue)

The issue author suggests reverting acff509 so that update_items falls back to Item._fields.keys() instead of Item._media_fields. That treats the symptom in one caller; this fix treats the root cause in Model.store() so any future caller that forwards a flex attribute through fields= is also safe. The change is also strictly narrower: existing fixed-column behaviour is byte-identical (the filter is a no-op when every entry of fields is a column).

Checklist

• Tests added
• Changelog entry added under "Bug fixes"
• poe test, poe lint, poe format, poe check-types all pass

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.62%. Comparing base (4e3884a) to head (bae9665).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6859      +/-   ##
==========================================
- Coverage   75.63%   75.62%   -0.01%     
==========================================
  Files         163      163              
  Lines       21312    21313       +1     
  Branches     3360     3360              
==========================================
- Hits        16119    16118       -1     
- Misses       4401     4402       +1     
- Partials      792      793       +1     

Files with missing lines	Coverage Δ
beets/dbcore/db.py	94.42% <100.00%> (+<0.01%)	⬆️

... and 1 file with indirect coverage changes

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