From b457068cf272bc9912187a2b7aaaa4445110735e Mon Sep 17 00:00:00 2001
From: Fabio Sangiovanni <sjh+github@sanjioh.org>
Date: Mon, 20 Jan 2020 20:50:30 +0100
Subject: [PATCH] Fixed #31187 -- Fixed detecting of existing total ordering in
 admin changelist when using Meta.constraints.

Detection of existing total ordering in admin changelist now takes into
account non-partial unique constraints.
---
 django/contrib/admin/views/main.py | 12 +++-
 tests/admin_changelist/tests.py    | 92 ++++++++++++++++++++++++++++++
 2 files changed, 102 insertions(+), 2 deletions(-)

diff --git a/django/contrib/admin/views/main.py b/django/contrib/admin/views/main.py
index b2d95828df..5bc3f736f1 100644
--- a/django/contrib/admin/views/main.py
+++ b/django/contrib/admin/views/main.py
@@ -367,8 +367,16 @@ class ChangeList:
                     break
                 ordering_fields.add(field.attname)
         else:
-            # No single total ordering field, try unique_together.
-            for field_names in self.lookup_opts.unique_together:
+            # No single total ordering field, try unique_together and total
+            # unique constraints.
+            constraint_field_names = (
+                *self.lookup_opts.unique_together,
+                *(
+                    constraint.fields
+                    for constraint in self.lookup_opts.total_unique_constraints
+                ),
+            )
+            for field_names in constraint_field_names:
                 # Normalize attname references by using get_field().
                 fields = [self.lookup_opts.get_field(field_name) for field_name in field_names]
                 # Composite unique constraints containing a nullable column
diff --git a/tests/admin_changelist/tests.py b/tests/admin_changelist/tests.py
index a4c220cb15..fa29886160 100644
--- a/tests/admin_changelist/tests.py
+++ b/tests/admin_changelist/tests.py
@@ -1058,6 +1058,98 @@ class ChangeListTests(TestCase):
             with self.subTest(ordering=ordering):
                 self.assertEqual(change_list._get_deterministic_ordering(ordering), expected)
 
+    @isolate_apps('admin_changelist')
+    def test_total_ordering_optimization_meta_constraints(self):
+        class Related(models.Model):
+            unique_field = models.BooleanField(unique=True)
+
+            class Meta:
+                ordering = ('unique_field',)
+
+        class Model(models.Model):
+            field_1 = models.BooleanField()
+            field_2 = models.BooleanField()
+            field_3 = models.BooleanField()
+            field_4 = models.BooleanField()
+            field_5 = models.BooleanField()
+            field_6 = models.BooleanField()
+            nullable_1 = models.BooleanField(null=True)
+            nullable_2 = models.BooleanField(null=True)
+            related_1 = models.ForeignKey(Related, models.CASCADE)
+            related_2 = models.ForeignKey(Related, models.CASCADE)
+            related_3 = models.ForeignKey(Related, models.CASCADE)
+            related_4 = models.ForeignKey(Related, models.CASCADE)
+
+            class Meta:
+                constraints = [
+                    *[
+                        models.UniqueConstraint(fields=fields, name=''.join(fields))
+                        for fields in (
+                            ['field_1'],
+                            ['nullable_1'],
+                            ['related_1'],
+                            ['related_2_id'],
+                            ['field_2', 'field_3'],
+                            ['field_2', 'nullable_2'],
+                            ['field_2', 'related_3'],
+                            ['field_3', 'related_4_id'],
+                        )
+                    ],
+                    models.CheckConstraint(check=models.Q(id__gt=0), name='foo'),
+                    models.UniqueConstraint(
+                        fields=['field_5'],
+                        condition=models.Q(id__gt=10),
+                        name='total_ordering_1',
+                    ),
+                    models.UniqueConstraint(
+                        fields=['field_6'],
+                        condition=models.Q(),
+                        name='total_ordering',
+                    ),
+                ]
+
+        class ModelAdmin(admin.ModelAdmin):
+            def get_queryset(self, request):
+                return Model.objects.none()
+
+        request = self._mocked_authenticated_request('/', self.superuser)
+        site = admin.AdminSite(name='admin')
+        model_admin = ModelAdmin(Model, site)
+        change_list = model_admin.get_changelist_instance(request)
+        tests = (
+            # Unique non-nullable field.
+            (['field_1'], ['field_1']),
+            # Unique nullable field.
+            (['nullable_1'], ['nullable_1', '-pk']),
+            # Related attname unique.
+            (['related_1_id'], ['related_1_id']),
+            (['related_2_id'], ['related_2_id']),
+            # Related ordering introspection is not implemented.
+            (['related_1'], ['related_1', '-pk']),
+            # Composite unique.
+            (['-field_2', 'field_3'], ['-field_2', 'field_3']),
+            # Composite unique nullable.
+            (['field_2', '-nullable_2'], ['field_2', '-nullable_2', '-pk']),
+            # Composite unique and nullable.
+            (
+                ['field_2', '-nullable_2', 'field_3'],
+                ['field_2', '-nullable_2', 'field_3'],
+            ),
+            # Composite field and related field name.
+            (['field_2', '-related_3'], ['field_2', '-related_3', '-pk']),
+            (['field_3', 'related_4'], ['field_3', 'related_4', '-pk']),
+            # Composite field and related field attname.
+            (['field_2', 'related_3_id'], ['field_2', 'related_3_id']),
+            (['field_3', '-related_4_id'], ['field_3', '-related_4_id']),
+            # Partial unique constraint is ignored.
+            (['field_5'], ['field_5', '-pk']),
+            # Unique constraint with an empty condition.
+            (['field_6'], ['field_6']),
+        )
+        for ordering, expected in tests:
+            with self.subTest(ordering=ordering):
+                self.assertEqual(change_list._get_deterministic_ordering(ordering), expected)
+
     def test_dynamic_list_filter(self):
         """
         Regression tests for ticket #17646: dynamic list_filter support.