Detect NULL default value as no default value.

This can happen when using `db_default=None` with `null=False` on a Django model field.

CHANGELOG.md

@@ -4,6 +4,9 @@ Feature:
 - **Breaking change**: Handle custom Django app label when gathering migrations from git reference. (#262)
 This means that, an app that was previously referenced by its folder name, will now be referenced by its Django app label.
 
+Bug:
+- Consider `DEFAULT NULL` as no default value being defined (#302)
+
 Miscellaneous:
 - Add py.typed file (#303)
 - Add support for Django 5.2 (#304)

src/django_migration_linter/sql_analyser/base.py

@@ -42,9 +42,9 @@ def has_not_null_column(sql_statements: list[str], **kwargs) -> bool:
             or sql.startswith("CREATE UNIQUE INDEX")
         ):
             not_null_column = True
-        if re.search("DEFAULT.*NOT NULL", sql):
+        if re.search("DEFAULT (?!NULL).*NOT NULL", sql):
             has_default_value = True
-        if "SET DEFAULT" in sql:
+        if "SET DEFAULT" in sql and "SET DEFAULT NULL" not in sql:
             has_default_value = True
         if "DROP DEFAULT" in sql:
             has_default_value = False

tests/fixtures.py

@@ -11,6 +11,9 @@ ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DEFAULT = "app_add_not_null_column_followed_by_d
 ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DB_DEFAULT = (
     "app_add_not_null_column_followed_by_db_default"
 )
+ADD_NOT_NULL_COLUMN_WITH_NULL_DB_DEFAULT = (
+    "app_add_not_null_column_with_null_db_default"
+)
 ALTER_COLUMN = "app_alter_column"
 ALTER_COLUMN_DROP_NOT_NULL = "app_alter_column_drop_not_null"
 DROP_UNIQUE_TOGETHER = "app_unique_together"

tests/functional/test_migration_linter.py

@@ -7,6 +7,7 @@ from unittest import skipIf
 import django
 from django.conf import settings
 from django.core.management import call_command
+from django.test import override_settings
 
 from django_migration_linter import MigrationLinter
 from tests import fixtures
@@ -166,6 +167,15 @@ class SqliteBackwardCompatibilityDetectionTestCase(
         app = fixtures.ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DB_DEFAULT
         self._test_linter_finds_errors(app)
 
+    @skipIf(django.VERSION[0] < 5, "db_default was implemented in Django 5.0")
+    @override_settings(
+        INSTALLED_APPS=settings.INSTALLED_APPS
+        + ["tests.test_project.app_add_not_null_column_with_null_db_default"]
+    )
+    def test_detected_not_null_column_with_null_db_default(self):
+        app = fixtures.ADD_NOT_NULL_COLUMN_WITH_NULL_DB_DEFAULT
+        self._test_linter_finds_errors(app)
+
     def test_detect_make_column_not_null_with_lib_default(self):
         # The 'django-add-default-value' doesn't handle sqlite correctly
         app = fixtures.MAKE_NOT_NULL_WITH_LIB_DEFAULT
@@ -177,6 +187,9 @@ class MySqlBackwardCompatibilityDetectionTestCase(
 ):
     databases = ["mysql"]
 
+    # test_detected_not_null_column_with_null_db_default is not included for mysql, because the setup raises
+    # django.db.utils.OperationalError: (1067, "Invalid default value for 'not_null_field_db_default_null'")
+
 
 class PostgresqlBackwardCompatibilityDetectionTestCase(
     BaseBackwardCompatibilityDetection, unittest.TestCase
@@ -191,3 +204,12 @@ class PostgresqlBackwardCompatibilityDetectionTestCase(
         linter = self._launch_linter(fixtures.CREATE_INDEX_EXCLUSIVE)
         self.assertFalse(linter.has_errors)
         self.assertTrue(linter.nb_warnings)
+
+    @skipIf(django.VERSION[0] < 5, "db_default was implemented in Django 5.0")
+    @override_settings(
+        INSTALLED_APPS=settings.INSTALLED_APPS
+        + ["tests.test_project.app_add_not_null_column_with_null_db_default"]
+    )
+    def test_detected_not_null_column_with_null_db_default(self):
+        app = fixtures.ADD_NOT_NULL_COLUMN_WITH_NULL_DB_DEFAULT
+        self._test_linter_finds_errors(app)

tests/test_project/app_add_not_null_column_with_null_db_default/migrations/0001_initial.py

@@ -0,0 +1,30 @@
+# Generated by Django 5.0.1 on 2024-02-04 20:07
+
+from __future__ import annotations
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = []
+
+    operations = [
+        migrations.CreateModel(
+            name="A",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("field", models.IntegerField()),
+            ],
+        ),
+    ]

tests/test_project/app_add_not_null_column_with_null_db_default/migrations/0002_a_not_null_field_with_null_db_default.py

@@ -0,0 +1,21 @@
+# Generated by Django 5.0.1 on 2024-02-04 20:07
+
+from __future__ import annotations
+
+import django.db.models.functions.math
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("app_add_not_null_column_with_null_db_default", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="a",
+            name="not_null_field_db_default_null",
+            field=models.IntegerField(db_default=None, default=None, null=False),
+        ),
+    ]

tests/test_project/app_add_not_null_column_with_null_db_default/models.py

@@ -0,0 +1,9 @@
+from __future__ import annotations
+
+from django.db import models
+from django.db.models.functions import Pi
+
+
+class A(models.Model):
+    field = models.IntegerField()
+    not_null_field_db_default_null = models.IntegerField(null=False, db_default=None)