From 60a17fccf4f2fa31b823b0f938005897f2f3ef16 Mon Sep 17 00:00:00 2001
From: Yassin Bahri <131185064+yassinbahri@users.noreply.github.com>
Date: Wed, 26 Aug 2026 10:34:57 +0200
Subject: [PATCH 1/2] Fixed #37300 -- Preserved parent instance hints on custom
 Prefetch querysets.

Regression in 821619aa8771ef211c4c4922001efdf914201ca3.

Thanks Norbert Kwizera for the report.
---
 .../db/models/fields/related_descriptors.py   |  2 ++
 docs/releases/6.1.1.txt                       |  5 +++
 tests/prefetch_related/tests.py               | 32 +++++++++++++++++++
 3 files changed, 39 insertions(+)

diff --git a/django/db/models/fields/related_descriptors.py b/django/db/models/fields/related_descriptors.py
index eafcb63ceb7c..32bc8d56c5c9 100644
--- a/django/db/models/fields/related_descriptors.py
+++ b/django/db/models/fields/related_descriptors.py
@@ -180,6 +180,7 @@ def get_prefetch_querysets(self, instances, querysets=None):
                     "length of 1."
                 )
             queryset = querysets[0]
+            queryset._add_hints(instance=instances[0])
         else:
             _cloning_disabled = True
             queryset = self.get_queryset(instance=instances[0])._disable_cloning()
@@ -480,6 +481,7 @@ def get_prefetch_querysets(self, instances, querysets=None):
                     "length of 1."
                 )
             queryset = querysets[0]
+            queryset._add_hints(instance=instances[0])
         else:
             _cloning_disabled = True
             queryset = self.get_queryset(instance=instances[0])._disable_cloning()
diff --git a/docs/releases/6.1.1.txt b/docs/releases/6.1.1.txt
index cfffb5fe5056..940c815c9b24 100644
--- a/docs/releases/6.1.1.txt
+++ b/docs/releases/6.1.1.txt
@@ -21,6 +21,11 @@ Bugfixes
   detect mixed ``on_delete`` variants for auto-created intermediate models for
   ``ManyToManyField``\s (:ticket:`37254`).
 
+* Fixed a regression in Django 6.1 where custom querysets used with
+  :class:`~django.db.models.Prefetch` for forward foreign key or reverse
+  one-to-one relationships were not routed using the parent queryset's
+  database (:ticket:`37300`).
+
 * Fixed a regression in Django 6.1 where HTML-safe strings, such as those
   created with :func:`~django.utils.safestring.mark_safe`, used as form media
   assets were treated as asset paths rather than being rendered verbatim
diff --git a/tests/prefetch_related/tests.py b/tests/prefetch_related/tests.py
index bda187a92a0a..eac01f8d6c54 100644
--- a/tests/prefetch_related/tests.py
+++ b/tests/prefetch_related/tests.py
@@ -1747,6 +1747,38 @@ def test_using_is_honored_custom_qs(self):
             )
         self.assertEqual(books, "Poems ()\n" "Sense and Sensibility ()\n")
 
+    def test_forward_fk_prefetch_custom_queryset_uses_parent_database(self):
+        book1 = Book.objects.using("default").create(title="Dive into Python")
+        Author.objects.using("default").create(name="Mark", first_book=book1)
+        book2 = Book.objects.using("other").create(title="Dive into Rust")
+        Author.objects.using("other").create(name="Mark", first_book=book2)
+
+        author = (
+            Author.objects.using("other")
+            .prefetch_related(Prefetch("first_book", queryset=Book.objects.all()))
+            .get(name="Mark")
+        )
+
+        self.assertEqual(author._state.db, "other")
+        self.assertEqual(author.first_book._state.db, "other")
+        self.assertEqual(author.first_book.title, "Dive into Rust")
+
+    def test_reverse_o2o_prefetch_custom_queryset_uses_parent_database(self):
+        BookWithYear.objects.using("default").create(title="Poems", published_year=2000)
+        BookWithYear.objects.using("other").create(title="Poems", published_year=2001)
+
+        book = (
+            Book.objects.using("other")
+            .prefetch_related(
+                Prefetch("bookwithyear", queryset=BookWithYear.objects.all())
+            )
+            .get(title="Poems")
+        )
+
+        self.assertEqual(book._state.db, "other")
+        self.assertEqual(book.bookwithyear._state.db, "other")
+        self.assertEqual(book.bookwithyear.published_year, 2001)
+
 
 class Ticket19607Tests(TestCase):
     @classmethod

From 5babd2e21ac0877d66c5452da17b97608b337fba Mon Sep 17 00:00:00 2001
From: Mariano Baragiola <mbaragiola@linux.com>
Date: Fri, 31 Jul 2026 23:34:30 -0300
Subject: [PATCH 2/2] Fixed #37237 -- Improved RelatedIn lookup preparation
 performance.

Thanks Simon Charette for the implementation idea.
---
 django/db/models/fields/related_lookups.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/django/db/models/fields/related_lookups.py b/django/db/models/fields/related_lookups.py
index 639c29d7ba4c..47a411125da7 100644
--- a/django/db/models/fields/related_lookups.py
+++ b/django/db/models/fields/related_lookups.py
@@ -66,6 +66,7 @@ def get_prep_lookup(self):
                         -1
                     ]
                     self.rhs = [target_field.get_prep_value(v) for v in self.rhs]
+                    self.prepare_rhs = False
             elif not getattr(self.rhs, "has_select_fields", True) and not getattr(
                 self.lhs.field.target_field, "primary_key", False
             ):