Fixed #32635 -- Fixed system check crash for reverse o2o relations in CheckConstraint.check and UniqueConstraint.condition.

Regression in b7b7df5fbc.

Thanks Szymon Zmilczak for the report.

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
                 ):

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`).

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()