Backport fixes from django-mssql-backend

README.md

@@ -135,10 +135,12 @@ Dictionary. Current available keys are:
    definition present in the ``freetds.conf`` FreeTDS configuration file
    instead of a hostname or an IP address.
 
-   But if this option is present and it's value is ``True``, this
-   special behavior is turned off.
+   But if this option is present and its value is ``True``, this
+   special behavior is turned off. Instead, connections to the database
+   server will be established using ``HOST`` and ``PORT`` options, without
+   requiring ``freetds.conf`` to be configured.
 
-   See http://www.freetds.org/userguide/dsnless.htm for more information.
+   See https://www.freetds.org/userguide/dsnless.html for more information.
 
 -  unicode_results
 

manage.py

@@ -1,7 +1,8 @@
+#!/usr/bin/env python
+
 # Copyright (c) Microsoft Corporation.
 # Licensed under the MIT license.
 
-#!/usr/bin/env python
 import os
 import sys
 

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
 
@@ -689,7 +690,7 @@ def add_field(self, model, field):
             self.connection.close()
 
     def _create_unique_sql(self, model, columns, name=None, condition=None, deferrable=None):
-        if (deferrable and not self.connection.features.supports_deferrable_unique_constraints):
+        if (deferrable and not getattr(self.connection.features, 'supports_deferrable_unique_constraints', False)):
             return None
 
         def create_unique_name(*args, **kwargs):
@@ -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)