Plugins/web: fix endpoints /…/values/… (#6158)

Following #4709 and #5447, the web plugin used single-quotes (ie. string
litteral) in the SQL query for table columns.

Thus, for instance, the query `GET /item/values/albumartist` would
return the litteral "albumartist" instead of a list of unique album
artists.

This prevents the Mopidy beets integration from working, returning the
single artist "albumartist".

beetsplug/web/__init__.py

@@ -17,9 +17,10 @@
 import base64
 import json
 import os
+import typing as t
 
 import flask
-from flask import g, jsonify
+from flask import jsonify
 from unidecode import unidecode
 from werkzeug.routing import BaseConverter, PathConverter
 
@@ -28,6 +29,17 @@ from beets import ui, util
 from beets.dbcore.query import PathQuery
 from beets.plugins import BeetsPlugin
 
+# Type checking hacks
+
+if t.TYPE_CHECKING:
+
+    class LibraryCtx(flask.ctx._AppCtxGlobals):
+        lib: beets.library.Library
+
+    g = LibraryCtx()
+else:
+    from flask import g
+
 # Utilities.
 
 
@@ -232,7 +244,7 @@ def _get_unique_table_field_values(model, field, sort_field):
         raise KeyError
     with g.lib.transaction() as tx:
         rows = tx.query(
-            f"SELECT DISTINCT '{field}' FROM '{model._table}' ORDER BY '{sort_field}'"
+            f"SELECT DISTINCT {field} FROM {model._table} ORDER BY {sort_field}"
         )
     return [row[0] for row in rows]
 

docs/changelog.rst

@@ -43,6 +43,10 @@ Bug fixes:
   accepted a list of strings). :bug:`5962`
 - Fix a bug introduced in release 2.4.0 where import from any valid
   import-log-file always threw a "none of the paths are importable" error.
+- :doc:`/plugins/web`: repair broken `/item/values/…` and `/albums/values/…`
+  endpoints. Previously, due to single-quotes (ie. string literal) in the SQL
+  query, the query eg. `GET /item/values/albumartist` would return the literal
+  "albumartist" instead of a list of unique album artists.
 
 For plugin developers:
 

test/plugins/test_web.py

@@ -118,6 +118,13 @@ class WebPluginTest(ItemInDBTestCase):
         assert response.status_code == 200
         assert len(res_json["items"]) == 3
 
+    def test_get_unique_item_artist(self):
+        response = self.client.get("/item/values/artist")
+        res_json = json.loads(response.data.decode("utf-8"))
+
+        assert response.status_code == 200
+        assert res_json["values"] == ["", "AAA Singers"]
+
     def test_get_single_item_by_id(self):
         response = self.client.get("/item/1")
         res_json = json.loads(response.data.decode("utf-8"))