Fixed #32466 -- Corrected autocomplete to_field resolution for complex cases.

In MTI or ForeignKey as primary key cases, it is required to fetch the attname
from the field instance on the remote model in order to reliably resolve the
to_field_name.

Co-authored-by: Johannes Maron <info@johanneshoppe.com>
Co-authored-by: Mariusz Felisiak <felisiak.mariusz@gmail.com>
Co-authored-by: Carlton Gibson <carlton.gibson@noumenal.es>

tests/admin_views/models.py

@@ -338,6 +338,24 @@ class Child(models.Model):
             raise ValidationError('invalid')
 
 
+class PKChild(models.Model):
+    """
+    Used to check autocomplete to_field resolution when ForeignKey is PK.
+    """
+    parent = models.ForeignKey(Parent, models.CASCADE, primary_key=True)
+    name = models.CharField(max_length=128)
+
+    class Meta:
+        ordering = ['parent']
+
+    def __str__(self):
+        return self.name
+
+
+class Toy(models.Model):
+    child = models.ForeignKey(PKChild, models.CASCADE)
+
+
 class EmptyModel(models.Model):
     def __str__(self):
         return "Primary key = %s" % self.id
@@ -615,12 +633,26 @@ class Song(models.Model):
 class Employee(Person):
     code = models.CharField(max_length=20)
 
+    class Meta:
+        ordering = ['name']
+
 
 class WorkHour(models.Model):
     datum = models.DateField()
     employee = models.ForeignKey(Employee, models.CASCADE)
 
 
+class Manager(Employee):
+    """
+    A multi-layer MTI child.
+    """
+    pass
+
+
+class Bonus(models.Model):
+    recipient = models.ForeignKey(Manager, on_delete=models.CASCADE)
+
+
 class Question(models.Model):
     big_id = models.BigAutoField(primary_key=True)
     question = models.CharField(max_length=20)

tests/admin_views/test_autocomplete_view.py

@@ -12,7 +12,10 @@ from django.test import RequestFactory, override_settings
 from django.urls import reverse, reverse_lazy
 
 from .admin import AnswerAdmin, QuestionAdmin
-from .models import Answer, Author, Authorship, Book, Question
+from .models import (
+    Answer, Author, Authorship, Bonus, Book, Employee, Manager, Parent,
+    PKChild, Question, Toy, WorkHour,
+)
 from .tests import AdminViewBasicTestCase
 
 PAGINATOR_SIZE = AutocompleteJsonView.paginate_by
@@ -37,6 +40,12 @@ site.register(Question, QuestionAdmin)
 site.register(Answer, AnswerAdmin)
 site.register(Author, AuthorAdmin)
 site.register(Book, BookAdmin)
+site.register(Employee, search_fields=['name'])
+site.register(WorkHour, autocomplete_fields=['employee'])
+site.register(Manager, search_fields=['name'])
+site.register(Bonus, autocomplete_fields=['recipient'])
+site.register(PKChild, search_fields=['name'])
+site.register(Toy, autocomplete_fields=['child'])
 
 
 @contextmanager
@@ -118,6 +127,51 @@ class AutocompleteJsonViewTests(AdminViewBasicTestCase):
             'pagination': {'more': False},
         })
 
+    def test_to_field_resolution_with_mti(self):
+        """
+        to_field resolution should correctly resolve for target models using
+        MTI. Tests for single and multi-level cases.
+        """
+        tests = [
+            (Employee, WorkHour, 'employee'),
+            (Manager, Bonus, 'recipient'),
+        ]
+        for Target, Remote, related_name in tests:
+            with self.subTest(target_model=Target, remote_model=Remote, related_name=related_name):
+                o = Target.objects.create(name="Frida Kahlo", gender=2, code="painter", alive=False)
+                opts = {
+                    'app_label': Remote._meta.app_label,
+                    'model_name': Remote._meta.model_name,
+                    'field_name': related_name,
+                }
+                request = self.factory.get(self.url, {'term': 'frida', **opts})
+                request.user = self.superuser
+                response = AutocompleteJsonView.as_view(**self.as_view_args)(request)
+                self.assertEqual(response.status_code, 200)
+                data = json.loads(response.content.decode('utf-8'))
+                self.assertEqual(data, {
+                    'results': [{'id': str(o.pk), 'text': o.name}],
+                    'pagination': {'more': False},
+                })
+
+    def test_to_field_resolution_with_fk_pk(self):
+        p = Parent.objects.create(name="Bertie")
+        c = PKChild.objects.create(parent=p, name="Anna")
+        opts = {
+            'app_label': Toy._meta.app_label,
+            'model_name': Toy._meta.model_name,
+            'field_name': 'child',
+        }
+        request = self.factory.get(self.url, {'term': 'anna', **opts})
+        request.user = self.superuser
+        response = AutocompleteJsonView.as_view(**self.as_view_args)(request)
+        self.assertEqual(response.status_code, 200)
+        data = json.loads(response.content.decode('utf-8'))
+        self.assertEqual(data, {
+            'results': [{'id': str(c.pk), 'text': c.name}],
+            'pagination': {'more': False},
+        })
+
     def test_field_does_not_exist(self):
         request = self.factory.get(self.url, {'term': 'is', **self.opts, 'field_name': 'does_not_exist'})
         request.user = self.superuser