From a77c9a4229cfef790ec18001b2cd18bd9c4aedbc Mon Sep 17 00:00:00 2001
From: Hasan Ramezani <hasan.r67@gmail.com>
Date: Tue, 13 Apr 2021 11:51:19 +0200
Subject: [PATCH] Fixed #32635 -- Fixed system check crash for reverse o2o
 relations in CheckConstraint.check and UniqueConstraint.condition.

Regression in b7b7df5fbcf44e6598396905136cab5a19e9faff.

Thanks Szymon Zmilczak for the report.
---
 django/db/models/base.py                  |  2 ++
 docs/releases/3.2.1.txt                   |  4 +++
 tests/invalid_models_tests/test_models.py | 43 +++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/django/db/models/base.py b/django/db/models/base.py
index 55b1691166..cd5268bed1 100644
--- a/django/db/models/base.py
+++ b/django/db/models/base.py
@@ -2105,6 +2105,8 @@ class Model(metaclass=ModelBase):
                 # JOIN must happen at the first lookup.
                 first_lookup = lookups[0]
                 if (
+                    hasattr(field, 'get_transform') and
+                    hasattr(field, 'get_lookup') and
                     field.get_transform(first_lookup) is None and
                     field.get_lookup(first_lookup) is None
                 ):
diff --git a/docs/releases/3.2.1.txt b/docs/releases/3.2.1.txt
index 376efb0211..cc716782e5 100644
--- a/docs/releases/3.2.1.txt
+++ b/docs/releases/3.2.1.txt
@@ -22,3 +22,7 @@ Bugfixes
 
 * Restored, following a regression in Django 3.2, displaying an exception
   message on the technical 404 debug page (:ticket:`32637`).
+
+* Fixed a bug in Django 3.2 where a system check would crash on a reverse
+  one-to-one relationships in ``CheckConstraint.check`` or
+  ``UniqueConstraint.condition`` (:ticket:`32635`).
diff --git a/tests/invalid_models_tests/test_models.py b/tests/invalid_models_tests/test_models.py
index 6c3017ff47..958ad120ca 100644
--- a/tests/invalid_models_tests/test_models.py
+++ b/tests/invalid_models_tests/test_models.py
@@ -1694,6 +1694,27 @@ class ConstraintsTests(TestCase):
             ),
         ])
 
+    @skipUnlessDBFeature('supports_table_check_constraints')
+    def test_check_constraint_pointing_to_reverse_o2o(self):
+        class Model(models.Model):
+            parent = models.OneToOneField('self', models.CASCADE)
+
+            class Meta:
+                constraints = [
+                    models.CheckConstraint(
+                        name='name',
+                        check=models.Q(model__isnull=True),
+                    ),
+                ]
+
+        self.assertEqual(Model.check(databases=self.databases), [
+            Error(
+                "'constraints' refers to the nonexistent field 'model'.",
+                obj=Model,
+                id='models.E012',
+            ),
+        ])
+
     @skipUnlessDBFeature('supports_table_check_constraints')
     def test_check_constraint_pointing_to_m2m_field(self):
         class Model(models.Model):
@@ -1943,6 +1964,28 @@ class ConstraintsTests(TestCase):
             )
         ] if connection.features.supports_partial_indexes else [])
 
+    def test_unique_constraint_pointing_to_reverse_o2o(self):
+        class Model(models.Model):
+            parent = models.OneToOneField('self', models.CASCADE)
+
+            class Meta:
+                required_db_features = {'supports_partial_indexes'}
+                constraints = [
+                    models.UniqueConstraint(
+                        fields=['parent'],
+                        name='name',
+                        condition=models.Q(model__isnull=True),
+                    ),
+                ]
+
+        self.assertEqual(Model.check(databases=self.databases), [
+            Error(
+                "'constraints' refers to the nonexistent field 'model'.",
+                obj=Model,
+                id='models.E012',
+            ),
+        ] if connection.features.supports_partial_indexes else [])
+
     def test_deferrable_unique_constraint(self):
         class Model(models.Model):
             age = models.IntegerField()