Perf: batch guardian permission assignment in bulk-edit

bulk_edit.set_permissions and BulkEditObjectPermissionsView both
looped documents/objects and called set_permissions_for_object per
object, which itself calls guardian's assign_perm/remove_perm once
per (object, user) pair -- ~10-20+ queries per object, scaling with
selection size.

Added set_permissions_for_objects, a bulk equivalent that resolves
existing permission holders once across the whole batch (not once per
object) and applies changes with a small, batch-size-independent
number of queries per action instead of one per (object, user) pair.

Deliberately does not use guardian's queryset-aware assign_perm:
passing a list as the target routes to bulk_assign_perm, which skips
creating a direct permission row for anyone who already has the
permission via ANY group membership (checked via
ObjectPermissionChecker.has_perm, which is group-inheritance-aware) --
unlike the single-object assign_perm this replaces, which always
ensures a direct row via get_or_create. Losing that guarantee would
mean a later revocation of the group's grant silently strips access
an admin explicitly asked to be direct. Bulk-creates rows straight
against UserObjectPermission/GroupObjectPermission instead
(ignore_conflicts=True, relying on the existing (identity, permission,
object_pk) unique constraint), which preserves the original semantics
exactly while still batching every object and identity into one query
per action. Also raises Permission.DoesNotExist for an unrecognized
action name instead of silently no-op-ing, matching the original
per-object path -- BulkEditObjectsSerializer never actually validates
action keys against the raw client-supplied permissions dict, so this
is reachable from client input, not just internal callers.

Verified via CaptureQueriesContext: query count is now identical at 5
vs. 50 documents/objects (was 1,123 queries for 20 documents on the
Document path, 2,806 for 50 tags on the BulkEditObjectPermissionsView
path, both now flat). Full documents test suite green (2,148 passed,
1 skipped).

src/documents/tests/test_api_objects.py

@@ -2,10 +2,15 @@ import datetime
 import json
 from unittest import mock
 
+from django.contrib.auth.models import Group
 from django.contrib.auth.models import Permission
 from django.contrib.auth.models import User
+from django.db import connection
 from django.test import override_settings
+from django.test.utils import CaptureQueriesContext
 from guardian.shortcuts import assign_perm
+from guardian.shortcuts import get_groups_with_perms
+from guardian.shortcuts import get_users_with_perms
 from rest_framework import status
 from rest_framework.test import APITestCase
 
@@ -815,6 +820,59 @@ class TestBulkEditObjects(APITestCase):
         self.assertEqual(response.status_code, status.HTTP_200_OK)
         self.assertEqual(StoragePath.objects.count(), 0)
 
+    def test_bulk_objects_set_permissions_query_count_independent_of_object_count(
+        self,
+    ) -> None:
+        """
+        GIVEN:
+            - Many tags are being bulk-edited to set permissions at once
+        WHEN:
+            - bulk_edit_objects API endpoint is called with set_permissions
+              operation over a small batch vs. a much larger one
+        THEN:
+            - The number of queries issued is the same either way -- each
+              user/group is applied across all tags with one batched call,
+              not one call per (tag, user) pair
+        """
+        group1 = Group.objects.create(name="perm-group")
+        permissions = {
+            "view": {"users": [self.user1.id, self.user2.id], "groups": [group1.id]},
+            "change": {"users": [self.user1.id], "groups": [group1.id]},
+        }
+
+        def run_with_n_tags(n: int) -> int:
+            tags = [Tag.objects.create(name=f"perm-tag-{n}-{i}") for i in range(n)]
+            with CaptureQueriesContext(connection) as ctx:
+                response = self.client.post(
+                    "/api/bulk_edit_objects/",
+                    json.dumps(
+                        {
+                            "objects": [t.id for t in tags],
+                            "object_type": "tags",
+                            "operation": "set_permissions",
+                            "permissions": permissions,
+                            "merge": False,
+                        },
+                    ),
+                    content_type="application/json",
+                )
+            self.assertEqual(response.status_code, status.HTTP_200_OK)
+            for tag in tags:
+                self.assertEqual(get_users_with_perms(tag).count(), 2)
+                self.assertEqual(get_groups_with_perms(tag).count(), 1)
+            return len(ctx.captured_queries)
+
+        small_batch_queries = run_with_n_tags(5)
+        large_batch_queries = run_with_n_tags(50)
+
+        self.assertEqual(
+            small_batch_queries,
+            large_batch_queries,
+            "Expected the same query count regardless of tag count, got "
+            f"{small_batch_queries} queries for 5 tags vs. "
+            f"{large_batch_queries} for 50",
+        )
+
     def test_bulk_objects_delete_all_filtered(self) -> None:
         """
         GIVEN:

src/documents/tests/test_bulk_edit.py

@@ -5,8 +5,11 @@ from unittest import mock
 
 import pikepdf
 from django.contrib.auth.models import Group
+from django.contrib.auth.models import Permission
 from django.contrib.auth.models import User
+from django.db import connection
 from django.test import TestCase
+from django.test.utils import CaptureQueriesContext
 from guardian.shortcuts import assign_perm
 from guardian.shortcuts import get_groups_with_perms
 from guardian.shortcuts import get_users_with_perms
@@ -19,6 +22,7 @@ from documents.models import Document
 from documents.models import DocumentType
 from documents.models import StoragePath
 from documents.models import Tag
+from documents.permissions import set_permissions_for_objects
 from documents.tests.utils import DirectoriesMixin
 
 
@@ -510,6 +514,131 @@ class TestBulkEdit(DirectoriesMixin, TestCase):
         )
         self.assertEqual(groups_with_perms.count(), 2)
 
+    @mock.patch("documents.tasks.bulk_update_documents.apply_async")
+    def test_set_permissions_query_count_independent_of_document_count(
+        self,
+        m,
+    ) -> None:
+        """
+        GIVEN:
+            - Many documents are being bulk-edited to set permissions at once
+        WHEN:
+            - set_permissions runs over a small batch vs. a much larger one
+        THEN:
+            - The number of queries issued is the same either way -- each
+              user/group is applied across all documents with one batched
+              call, not one call per (document, user) pair
+        """
+        permissions = {
+            "view": {
+                "users": [self.user1.id, self.user2.id],
+                "groups": [self.group2.id],
+            },
+            "change": {
+                "users": [self.user1.id],
+                "groups": [self.group2.id],
+            },
+        }
+
+        def run_with_n_documents(n: int) -> int:
+            docs = [
+                Document.objects.create(checksum=f"perm-{n}-{i}", title=f"perm-{n}-{i}")
+                for i in range(n)
+            ]
+            with CaptureQueriesContext(connection) as ctx:
+                bulk_edit.set_permissions(
+                    [doc.id for doc in docs],
+                    set_permissions=permissions,
+                    owner=self.owner,
+                    merge=False,
+                )
+            for doc in docs:
+                self.assertEqual(get_users_with_perms(doc).count(), 2)
+                self.assertEqual(get_groups_with_perms(doc).count(), 1)
+            return len(ctx.captured_queries)
+
+        small_batch_queries = run_with_n_documents(5)
+        large_batch_queries = run_with_n_documents(50)
+
+        self.assertEqual(
+            small_batch_queries,
+            large_batch_queries,
+            "Expected the same query count regardless of document count, got "
+            f"{small_batch_queries} queries for 5 documents vs. "
+            f"{large_batch_queries} for 50",
+        )
+
+    @mock.patch("documents.tasks.bulk_update_documents.apply_async")
+    def test_set_permissions_grants_direct_perm_even_if_already_granted_via_group(
+        self,
+        m,
+    ) -> None:
+        """
+        GIVEN:
+            - A user already has view access to a document via group
+              membership, with no direct grant of their own
+        WHEN:
+            - set_permissions explicitly grants that same user direct view
+              access via bulk_edit
+        THEN:
+            - A direct permission grant is created for the user, not skipped
+              because they already have equivalent access via the group
+
+        Regression test: guardian's queryset-aware assign_perm() (routed to
+        when the target is a list/queryset) skips creating a direct row for
+        anyone whose ObjectPermissionChecker.has_perm() already returns True
+        -- which includes group-derived access. The single-object assign_perm
+        this bulk path replaces has no such check; it always ensures a
+        direct row via get_or_create. Losing that guarantee would mean
+        revoking the group's grant later silently strips access that was
+        supposed to be explicit.
+        """
+        self.doc1.owner = self.user1
+        self.doc1.save()
+        self.user1.groups.add(self.group1)
+        assign_perm("view_document", self.group1, self.doc1)
+
+        bulk_edit.set_permissions(
+            [self.doc1.id],
+            set_permissions={
+                "view": {"users": [self.user1.id], "groups": []},
+            },
+            merge=True,
+        )
+
+        direct_users = get_users_with_perms(
+            self.doc1,
+            only_with_perms_in=["view_document"],
+            with_group_users=False,
+        )
+        self.assertIn(self.user1, direct_users)
+
+    def test_set_permissions_for_objects_raises_for_unknown_action(self) -> None:
+        """
+        GIVEN:
+            - An unrecognized permission action name with users to grant it
+              to
+        WHEN:
+            - set_permissions_for_objects is called
+        THEN:
+            - Permission.DoesNotExist is raised, not a silent no-op
+
+        Regression test: the endpoint that calls this
+        (BulkEditObjectPermissionsView) never actually validates action
+        names against the raw client-supplied permissions dict --
+        BulkEditObjectsSerializer._validate_permissions calls
+        validate_set_permissions() only for its side-effecting user/group id
+        checks and discards the filtered dict it returns -- so a bogus
+        action key reaches this function as-is. Resolving the Permission via
+        a bare `.filter()` (which returns empty instead of raising) would
+        silently drop the grant and report success.
+        """
+        with self.assertRaises(Permission.DoesNotExist):
+            set_permissions_for_objects(
+                {"not_a_real_action": {"users": [self.user1.id], "groups": []}},
+                [self.doc1],
+            )
+
     @mock.patch("documents.models.Document.delete")
     def test_delete_documents_old_uuid_field(self, m) -> None:
         m.side_effect = Exception("Data too long for column 'transaction_id' at row 1")