Resolve primary key name correctly.

docs/changelog.rst

@@ -4,6 +4,7 @@ Changelog
 v4.3.0 (202X-XX-XX)
 -------------------
 
+* Fixed `Resolve primary key name correctly. <https://github.com/jazzband/django-polymorphic/pull/620>`_
 * Implemented `Include get_child_inlines() hook in stacked inline admin forms. <https://github.com/jazzband/django-polymorphic/pull/681>`_
 * Fixed `multi-database support in inheritance accessors. <https://github.com/jazzband/django-polymorphic/pull/550>`_
 * Fixed `Caching in inheritance accessor functions <https://github.com/jazzband/django-polymorphic/pull/510>`_

src/polymorphic/base.py

@@ -79,10 +79,8 @@ def __new__(self, model_name, bases, attrs, **kwargs):
 
         # determine the name of the primary key field and store it into the class variable
         # polymorphic_primary_key_name (it is needed by query.py)
-        for f in new_class._meta.fields:
-            if f.primary_key and type(f) is not models.OneToOneField:
-                new_class.polymorphic_primary_key_name = f.name
-                break
+        if new_class._meta.pk:
+            new_class.polymorphic_primary_key_name = new_class._meta.pk.name
 
         return new_class
 

src/polymorphic/tests/migrations/0001_initial.py

@@ -1,5 +1,6 @@
-# Generated by Django 4.2.26 on 2025-12-05 02:34
+# Generated by Django 4.2.27 on 2025-12-08 15:20
 
+from django.conf import settings
 from django.db import migrations, models
 import django.db.models.deletion
 import django.db.models.manager
@@ -17,6 +18,17 @@ class Migration(migrations.Migration):
     ]
 
     operations = [
+        migrations.CreateModel(
+            name='Account',
+            fields=[
+                ('user', models.OneToOneField(on_delete=django.db.models.deletion.CASCADE, primary_key=True, related_name='account', serialize=False, to=settings.AUTH_USER_MODEL)),
+                ('polymorphic_ctype', models.ForeignKey(editable=False, null=True, on_delete=django.db.models.deletion.CASCADE, related_name='polymorphic_%(app_label)s.%(class)s_set+', to='contenttypes.contenttype')),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+        ),
         migrations.CreateModel(
             name='Base',
             fields=[
@@ -599,6 +611,30 @@ class Migration(migrations.Migration):
             },
             bases=('tests.relationbase',),
         ),
+        migrations.CreateModel(
+            name='SpecialAccount1',
+            fields=[
+                ('account_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.account')),
+                ('extra1', models.IntegerField(blank=True, default=None, null=True)),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+            bases=('tests.account',),
+        ),
+        migrations.CreateModel(
+            name='SpecialAccount2',
+            fields=[
+                ('account_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.account')),
+                ('extra1', models.CharField(blank=True, default='', max_length=30)),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+            bases=('tests.account',),
+        ),
         migrations.CreateModel(
             name='SubclassSelectorAbstractConcreteModel',
             fields=[
@@ -1060,6 +1096,18 @@ class Migration(migrations.Migration):
             },
             bases=('tests.relationb',),
         ),
+        migrations.CreateModel(
+            name='SpecialAccount1_1',
+            fields=[
+                ('specialaccount1_ptr', models.OneToOneField(auto_created=True, on_delete=django.db.models.deletion.CASCADE, parent_link=True, primary_key=True, serialize=False, to='tests.specialaccount1')),
+                ('extra2', models.IntegerField(blank=True, default=None, null=True)),
+            ],
+            options={
+                'abstract': False,
+                'base_manager_name': 'objects',
+            },
+            bases=('tests.specialaccount1',),
+        ),
         migrations.CreateModel(
             name='SubclassSelectorProxyConcreteModel',
             fields=[

src/polymorphic/tests/models.py

@@ -2,6 +2,7 @@
 
 import django
 from django.contrib.auth.models import Group
+from django.contrib.auth import get_user_model
 from django.contrib.contenttypes.models import ContentType
 from django.db import models
 from django.db.models.query import QuerySet
@@ -565,3 +566,21 @@ class Meta:
 class PurpleHeadDuck(HomeDuck, BlueHeadDuck):
     class Meta:
         proxy = True
+
+
+class Account(PolymorphicModel):
+    user = models.OneToOneField(
+        get_user_model(), primary_key=True, on_delete=models.CASCADE, related_name="account"
+    )
+
+
+class SpecialAccount1(Account):
+    extra1 = models.IntegerField(null=True, default=None, blank=True)
+
+
+class SpecialAccount1_1(SpecialAccount1):
+    extra2 = models.IntegerField(null=True, default=None, blank=True)
+
+
+class SpecialAccount2(Account):
+    extra1 = models.CharField(default="", blank=True, max_length=30)

src/polymorphic/tests/test_orm.py

@@ -2,6 +2,7 @@
 import re
 import uuid
 
+from django.contrib.auth import get_user_model
 from django.contrib.contenttypes.models import ContentType
 from django.db import models, connection
 from django.db.models import Case, Count, FilteredRelation, Q, Sum, When, Exists, OuterRef
@@ -94,6 +95,10 @@
     UUIDResearchProject,
     Duck,
     PurpleHeadDuck,
+    Account,
+    SpecialAccount1,
+    SpecialAccount1_1,
+    SpecialAccount2,
 )
 
 
@@ -1521,3 +1526,94 @@ def test_subqueries(self):
         InlineParent.objects.all().delete()
         InlineModelA.objects.all().delete()
         InlineModelB.objects.all().delete()
+
+    def test_one_to_one_primary_key(self):
+        # check pk name resolution
+        for mdl in [Account, SpecialAccount1, SpecialAccount1_1, SpecialAccount2]:
+            assert mdl.polymorphic_primary_key_name == mdl._meta.pk.name
+
+        user1 = get_user_model().objects.create(
+            username="user1", email="user1@example.com", password="password"
+        )
+        user2 = get_user_model().objects.create(
+            username="user2", email="user2@example.com", password="password"
+        )
+        user3 = get_user_model().objects.create(
+            username="user3", email="user3@example.com", password="password"
+        )
+        user4 = get_user_model().objects.create(
+            username="user4", email="user4@example.com", password="password"
+        )
+
+        user1_profile = SpecialAccount1_1.objects.create(user=user1, extra1=5, extra2=6)
+
+        user2_profile = SpecialAccount1.objects.create(user=user2, extra1=5)
+
+        user3_profile = SpecialAccount2.objects.create(user=user3, extra1="test")
+
+        user4_profile = SpecialAccount1_1.objects.create(user=user4, extra1=7, extra2=8)
+
+        user1.refresh_from_db()
+        assert user1.account.__class__ is SpecialAccount1_1
+        assert user1.account.extra1 == 5
+        assert user1.account.extra2 == 6
+        assert user1_profile.pk == user1.account.pk
+
+        user2.refresh_from_db()
+        assert user2.account.__class__ is SpecialAccount1
+        assert user2.account.extra1 == 5
+        assert user2_profile.pk == user2.account.pk
+        assert not hasattr(user2.account, "extra2")
+
+        user3.refresh_from_db()
+        assert user3.account.__class__ is SpecialAccount2
+        assert user3.account.extra1 == "test"
+        assert user3_profile.pk == user3.account.pk
+        assert not hasattr(user3.account, "extra2")
+
+        user4.refresh_from_db()
+        assert user4.account.__class__ is SpecialAccount1_1
+        assert user4.account.extra1 == 7
+        assert user4.account.extra2 == 8
+        assert user4_profile.pk == user4.account.pk
+
+        assert get_user_model().objects.filter(pk=user2.pk).delete() == (
+            3,
+            {"tests.SpecialAccount1": 1, "tests.Account": 1, "auth.User": 1},
+        )
+
+        assert SpecialAccount1.objects.count() == 2
+        assert Account.objects.count() == 3
+
+        remaining = get_user_model().objects.filter(
+            pk__in=[user1.pk, user2.pk, user3.pk, user4.pk]
+        )
+        assert remaining.count() == 3
+        for usr, expected in zip(
+            remaining.order_by("pk"), (user1_profile, user3_profile, user4_profile)
+        ):
+            assert usr.account == expected
+
+        assert get_user_model().objects.filter(pk__in=[user3.pk]).delete() == (
+            3,
+            {"tests.SpecialAccount2": 1, "tests.Account": 1, "auth.User": 1},
+        )
+
+        assert Account.objects.count() == 2
+
+        assert SpecialAccount1_1.objects.all().delete() == (
+            6,
+            {"tests.SpecialAccount1_1": 2, "tests.SpecialAccount1": 2, "tests.Account": 2},
+        )
+
+        assert Account.objects.count() == 0
+
+        remaining = get_user_model().objects.filter(pk__gte=user1.pk)
+        assert remaining.count() == 2
+        for usr in remaining:
+            assert not hasattr(usr, "account")
+
+        assert get_user_model().objects.filter(pk__in=[user1.pk, user4.pk]).delete() == (
+            2,
+            {"auth.User": 2},
+        )