Fixed #30368 -- Fixed prefetch_related() for GenericForeignKey when PK is also a FK.

AUTHORS

@@ -880,6 +880,7 @@ answer newbie questions, and generally made Django that much better:
     Vinay Karanam <https://github.com/vinayinvicible>
     Vinay Sajip <vinay_sajip@yahoo.co.uk>
     Vincent Foley <vfoleybourgon@yahoo.ca>
+    Vinny Do <vdo.code@gmail.com>
     Vitaly Babiy <vbabiy86@gmail.com>
     Vladimir Kuzma <vladimirkuzma.ch@gmail.com>
     Vlado <vlado@labath.org>

django/db/models/fields/related.py

@@ -939,6 +939,9 @@ class ForeignKey(ForeignObject):
     def get_db_prep_value(self, value, connection, prepared=False):
         return self.target_field.get_db_prep_value(value, connection, prepared)
 
+    def get_prep_value(self, value):
+        return self.target_field.get_prep_value(value)
+
     def contribute_to_related_class(self, cls, related):
         super().contribute_to_related_class(cls, related)
         if self.remote_field.field_name is None:

tests/prefetch_related/tests.py

@@ -891,6 +891,13 @@ class GenericRelationTests(TestCase):
         qs = Comment.objects.prefetch_related('content_object_uuid')
         self.assertEqual([c.content_object_uuid for c in qs], [article])
 
+    def test_prefetch_GFK_fk_pk(self):
+        book = Book.objects.create(title='Poems')
+        book_with_year = BookWithYear.objects.create(book=book, published_year=2019)
+        Comment.objects.create(comment='awesome', content_object=book_with_year)
+        qs = Comment.objects.prefetch_related('content_object')
+        self.assertEqual([c.content_object for c in qs], [book_with_year])
+
     def test_traverse_GFK(self):
         """
         A 'content_object' can be traversed with prefetch_related() and