Error on unsupported unique constraint conditions

CREATE INDEX in SQL Server only supports AND conditions (not OR) as part
of its WHERE syntax. This change handles that situation by raising an
error from the schema editor class. This change adds unit tests to
confirm this happens against a SQL Server database.

Previously opened at ESSolutions/django-mssql-backend#97

Author: davidjb

mssql/schema.py

@@ -17,8 +17,9 @@
     Table,
 )
 from django import VERSION as django_version
-from django.db.models import Index
+from django.db.models import Index, UniqueConstraint
 from django.db.models.fields import AutoField, BigAutoField
+from django.db.models.sql.where import AND
 from django.db.transaction import TransactionManagementError
 from django.utils.encoding import force_str
 
@@ -955,3 +956,9 @@ def remove_field(self, model, field):
         for sql in list(self.deferred_sql):
             if isinstance(sql, Statement) and sql.references_column(model._meta.db_table, field.column):
                 self.deferred_sql.remove(sql)
+
+    def add_constraint(self, model, constraint):
+        if isinstance(constraint, UniqueConstraint) and constraint.condition and constraint.condition.connector != AND:
+            raise NotImplementedError("The backend does not support %s conditions on unique constraint %s." %
+                                      (constraint.condition.connector, constraint.name))
+        super().add_constraint(model, constraint)

testapp/migrations/0010_test_unique_constraints.py

@@ -0,0 +1,68 @@
+# Generated by Django 3.1.5 on 2021-01-18 00:05
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('testapp', '0009_test_drop_table_with_foreign_key_reference_part2'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='TestUnsupportableUniqueConstraint',
+            fields=[
+                (
+                    'id',
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name='ID',
+                    ),
+                ),
+                ('_type', models.CharField(max_length=50)),
+                ('status', models.CharField(max_length=50)),
+            ],
+            options={
+                'managed': False,
+            },
+        ),
+        migrations.CreateModel(
+            name='TestSupportableUniqueConstraint',
+            fields=[
+                (
+                    'id',
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name='ID',
+                    ),
+                ),
+                ('_type', models.CharField(max_length=50)),
+                ('status', models.CharField(max_length=50)),
+            ],
+        ),
+        migrations.AddConstraint(
+            model_name='testsupportableuniqueconstraint',
+            constraint=models.UniqueConstraint(
+                condition=models.Q(
+                    ('status', 'in_progress'),
+                    ('status', 'needs_changes'),
+                    ('status', 'published'),
+                ),
+                fields=('_type',),
+                name='and_constraint',
+            ),
+        ),
+        migrations.AddConstraint(
+            model_name='testsupportableuniqueconstraint',
+            constraint=models.UniqueConstraint(
+                condition=models.Q(status__in=['in_progress', 'needs_changes']),
+                fields=('_type',),
+                name='in_constraint',
+            ),
+        ),
+    ]

testapp/models.py

@@ -4,6 +4,7 @@
 import uuid
 
 from django.db import models
+from django.db.models import Q
 from django.utils import timezone
 
 
@@ -74,3 +75,39 @@ class TestRemoveOneToOneFieldModel(models.Model):
     # thats already is removed.
     # b = models.OneToOneField('self', on_delete=models.SET_NULL, null=True)
     a = models.CharField(max_length=50)
+
+
+class TestUnsupportableUniqueConstraint(models.Model):
+    class Meta:
+        managed = False
+        constraints = [
+            models.UniqueConstraint(
+                name='or_constraint',
+                fields=['_type'],
+                condition=(Q(status='in_progress') | Q(status='needs_changes')),
+            ),
+        ]
+
+    _type = models.CharField(max_length=50)
+    status = models.CharField(max_length=50)
+
+
+class TestSupportableUniqueConstraint(models.Model):
+    class Meta:
+        constraints = [
+            models.UniqueConstraint(
+                name='and_constraint',
+                fields=['_type'],
+                condition=(
+                    Q(status='in_progress') & Q(status='needs_changes') & Q(status='published')
+                ),
+            ),
+            models.UniqueConstraint(
+                name='in_constraint',
+                fields=['_type'],
+                condition=(Q(status__in=['in_progress', 'needs_changes'])),
+            ),
+        ]
+
+    _type = models.CharField(max_length=50)
+    status = models.CharField(max_length=50)

testapp/tests/test_constraints.py

@@ -1,12 +1,18 @@
 # Copyright (c) Microsoft Corporation.
 # Licensed under the MIT license.
 
+from django.db import connections, migrations, models
+from django.db.migrations.state import ProjectState
 from django.db.utils import IntegrityError
-from django.test import TestCase, skipUnlessDBFeature
+from django.test import TestCase, TransactionTestCase, skipUnlessDBFeature
 
+from mssql.base import DatabaseWrapper
 from ..models import (
-    Author, Editor, Post,
-    TestUniqueNullableModel, TestNullableUniqueTogetherModel,
+    Author,
+    Editor,
+    Post,
+    TestUniqueNullableModel,
+    TestNullableUniqueTogetherModel,
 )
 
 
@@ -55,3 +61,52 @@ def test_after_type_change(self):
         TestNullableUniqueTogetherModel.objects.create(a='aaa', b='bbb', c='ccc')
         with self.assertRaises(IntegrityError):
             TestNullableUniqueTogetherModel.objects.create(a='aaa', b='bbb', c='ccc')
+
+
+class TestUniqueConstraints(TransactionTestCase):
+    def test_unsupportable_unique_constraint(self):
+        # Only execute tests when running against SQL Server
+        connection = connections['default']
+        if isinstance(connection, DatabaseWrapper):
+
+            class TestMigration(migrations.Migration):
+                initial = True
+
+                operations = [
+                    migrations.CreateModel(
+                        name='TestUnsupportableUniqueConstraint',
+                        fields=[
+                            (
+                                'id',
+                                models.AutoField(
+                                    auto_created=True,
+                                    primary_key=True,
+                                    serialize=False,
+                                    verbose_name='ID',
+                                ),
+                            ),
+                            ('_type', models.CharField(max_length=50)),
+                            ('status', models.CharField(max_length=50)),
+                        ],
+                    ),
+                    migrations.AddConstraint(
+                        model_name='testunsupportableuniqueconstraint',
+                        constraint=models.UniqueConstraint(
+                            condition=models.Q(
+                                ('status', 'in_progress'),
+                                ('status', 'needs_changes'),
+                                _connector='OR',
+                            ),
+                            fields=('_type',),
+                            name='or_constraint',
+                        ),
+                    ),
+                ]
+
+            migration = TestMigration('testapp', 'test_unsupportable_unique_constraint')
+
+            with connection.schema_editor(atomic=True) as editor:
+                with self.assertRaisesRegex(
+                    NotImplementedError, "does not support OR conditions"
+                ):
+                    return migration.apply(ProjectState(), editor)