Cover boolean/non-numeric/non-list tag id rejection; fix overflow comment that maybe triggered Copilot

src/documents/serialisers.py

@@ -775,14 +775,9 @@ class _BatchingManyRelatedField(serializers.ManyRelatedField):
         item_pks = [(item, self._normalize_pk(item)) for item in data]
         candidate_pks = {pk for _, pk in item_pks if pk is not None}
 
-        # Django's IntegerFieldOverflow guard (-> EmptyResultSet, i.e. no
-        # match) only covers exact/gt/gte/lt/lte lookups, not `in` -- an
-        # out-of-range int in `pk__in=` reaches the DB driver as-is and
-        # raises OverflowError (SQLite) / DataError (Postgres) instead of
-        # cleanly matching nothing. The per-item `exact`-lookup fallback
-        # below IS covered, so on that failure just skip the batch and let
-        # every item resolve individually -- each still costs one query,
-        # but reports the normal validation error instead of a raw 500.
+        # Django's overflow guard covers exact/gt/gte/lt/lte, not `in` -- an
+        # out-of-range pk in `pk__in=` can hit the driver raw (OverflowError
+        # on SQLite). Fall back to per-item resolution, which is guarded.
         try:
             resolved_by_pk = {
                 obj.pk: obj

src/documents/tests/test_api_documents.py

@@ -331,6 +331,84 @@ class TestDocumentApi(DirectoriesMixin, ConsumeTaskMixin, APITestCase):
 
         self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
 
+    def test_document_update_tags_rejects_boolean_id(self) -> None:
+        """
+        GIVEN:
+            - A document is being updated with a boolean submitted as a tag id
+            - A tag exists with id 1
+        WHEN:
+            - API PATCH request is made setting the document's tags to [true]
+        THEN:
+            - A normal 400 validation error is returned
+            - The document is not silently given tag id 1 (`True == 1`)
+        """
+        # Explicit pk, not TagFactory()'s auto-assigned id: Postgres sequences
+        # aren't rolled back between tests in the same TestCase (only the
+        # rows are), so relying on this being the first tag created would be
+        # order-dependent.
+        Tag.objects.create(name="t", pk=1)
+        doc = Document.objects.create(
+            title="none",
+            checksum="123",
+            mime_type="application/pdf",
+        )
+
+        response = self.client.patch(
+            f"/api/documents/{doc.pk}/",
+            {"tags": [True]},
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+        doc.refresh_from_db()
+        self.assertEqual(doc.tags.count(), 0)
+
+    def test_document_update_tags_rejects_non_numeric_id(self) -> None:
+        """
+        GIVEN:
+            - A document is being updated with a non-numeric tag id
+        WHEN:
+            - API PATCH request is made setting the document's tags
+        THEN:
+            - A normal 400 validation error is returned
+        """
+        doc = Document.objects.create(
+            title="none",
+            checksum="123",
+            mime_type="application/pdf",
+        )
+
+        response = self.client.patch(
+            f"/api/documents/{doc.pk}/",
+            {"tags": ["not-a-number"]},
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+
+    def test_document_update_tags_rejects_non_list(self) -> None:
+        """
+        GIVEN:
+            - A document is being updated
+        WHEN:
+            - API PATCH request is made with a non-list value for tags
+        THEN:
+            - A normal 400 validation error is returned
+        """
+        doc = Document.objects.create(
+            title="none",
+            checksum="123",
+            mime_type="application/pdf",
+        )
+
+        response = self.client.patch(
+            f"/api/documents/{doc.pk}/",
+            {"tags": "not-a-list"},
+            format="json",
+        )
+
+        self.assertEqual(response.status_code, status.HTTP_400_BAD_REQUEST)
+
     def test_document_update_legacy_created_format(self) -> None:
         """
         GIVEN: