Support Django 5.0 db_default attribute.

A DB default is not considered backward incompatible, as the default value is kept on DB-level.
See https://docs.djangoproject.com/en/dev/releases/5.0/#database-computed-default-values

CHANGELOG.md

@@ -1,5 +1,8 @@
 ## 5.x.y
 
+Feature:
+- Support Django 5.0 `db_default` attribute (issue #275)
+
 Bug:
 - Don't detect 'IS NOT NULL' as backward incompatible changes (issue #263)
 

docs/incompatibilities.md

@@ -71,7 +71,7 @@ Only rolling back the code will make all new insertions crash because Django doe
 One would think that adding a default value in Django will prevent these errors.
 
 A common misconception is that the Django default value is translated to a database default.
-But Django actually uses the default value to fill new new column on existing rows and to set an unspecified column value to its default.
+But Django actually uses the default value to fill the new column on existing rows and to set an unspecified column value to its default.
 The latter is done at the application level, by Django and not by the database because the default value was dropped during migration.
 You can read more about this in the [Django and its default values blog post](https://medium.com/botify-labs/django-and-its-default-values-c21a13cff9f).
 
@@ -90,6 +90,7 @@ You can read more about this in the [Django and its default values blog post](ht
 
 :white_check_mark: **Solutions**:
 - Make the column nullable
+- Set a database default using the Django 5.0 attribute `db_default`. See the [Django docs](https://docs.djangoproject.com/en/dev/releases/5.0/#database-computed-default-values)
 - Set a database default using Django's [RunSQL](https://docs.djangoproject.com/en/dev/ref/migration-operations/#django.db.migrations.operations.RunSQL)
 - Set a database default using [django-add-default-value](https://github.com/3YOURMIND/django-add-default-value/)
 

src/django_migration_linter/sql_analyser/base.py

@@ -32,20 +32,22 @@ def update_migration_checks(
 
 def has_not_null_column(sql_statements: list[str], **kwargs) -> bool:
     # TODO: improve to detect that the same column is concerned
-    ends_with_default = False
+    not_null_column = False
+    has_default_value = False
+
     for sql in sql_statements:
+        if re.search("(?<!DROP )(?<!IS )NOT NULL", sql) and not (
+            sql.startswith("CREATE TABLE") or sql.startswith("CREATE INDEX")
+        ):
+            not_null_column = True
+        if re.search("DEFAULT.*NOT NULL", sql):
+            has_default_value = True
         if "SET DEFAULT" in sql:
-            ends_with_default = True
-        elif "DROP DEFAULT" in sql:
-            ends_with_default = False
-    return (
-        any(
-            re.search("(?<!DROP )(?<!IS )NOT NULL", sql)
-            and not (sql.startswith("CREATE TABLE") or sql.startswith("CREATE INDEX"))
-            for sql in sql_statements
-        )
-        and ends_with_default is False
-    )
+            has_default_value = True
+        if "DROP DEFAULT" in sql:
+            has_default_value = False
+
+    return not_null_column and not has_default_value
 
 
 def has_add_unique(sql_statements: list[str], **kwargs) -> bool:

tests/fixtures.py

@@ -8,6 +8,9 @@ RENAME_COLUMN = "app_rename_column"
 RENAME_TABLE = "app_rename_table"
 IGNORE_MIGRATION = "app_ignore_migration"
 ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DEFAULT = "app_add_not_null_column_followed_by_default"
+ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DB_DEFAULT = (
+    "app_add_not_null_column_followed_by_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

@@ -2,7 +2,9 @@ from __future__ import annotations
 
 import os
 import unittest
+from unittest import skipIf
 
+import django
 from django.conf import settings
 from django.core.management import call_command
 
@@ -88,6 +90,11 @@ class BaseBackwardCompatibilityDetection:
         app = fixtures.ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DEFAULT
         self._test_linter_finds_no_errors(app)
 
+    @skipIf(django.VERSION[0] < 5, "db_default was implemented in Django 5.0")
+    def test_accept_not_null_column_followed_by_adding_db_default(self):
+        app = fixtures.ADD_NOT_NULL_COLUMN_FOLLOWED_BY_DB_DEFAULT
+        self._test_linter_finds_no_errors(app)
+
     def test_detect_alter_column(self):
         app = fixtures.ALTER_COLUMN
         self._test_linter_finds_no_errors(app)
@@ -128,6 +135,11 @@ class SqliteBackwardCompatibilityDetectionTestCase(
         app = fixtures.MAKE_NOT_NULL_WITH_DJANGO_DEFAULT
         self._test_linter_finds_errors(app)
 
+    @skipIf(django.VERSION[0] < 5, "db_default was implemented in Django 5.0")
+    def test_accept_not_null_column_followed_by_adding_db_default(self):
+        app = fixtures.ADD_NOT_NULL_COLUMN_FOLLOWED_BY_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

tests/test_project/app_add_not_null_column_followed_by_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_followed_by_db_default/migrations/0002_a_not_null_field_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_followed_by_db_default", "0001_initial"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="a",
+            name="not_null_field_db_default",
+            field=models.IntegerField(db_default=django.db.models.functions.math.Pi()),
+        ),
+    ]

tests/test_project/app_add_not_null_column_followed_by_db_default/models.py

@@ -0,0 +1,12 @@
+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 = models.IntegerField(
+        null=False,
+        db_default=Pi(),
+    )

tests/test_project/settings.py

@@ -14,6 +14,8 @@ from __future__ import annotations
 
 import os
 
+import django
+
 # Build paths inside the project like this: os.path.join(BASE_DIR, ...)
 BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
 
@@ -59,6 +61,12 @@ INSTALLED_APPS = [
     "tests.test_project.app_create_index_exclusive",
 ]
 
+if django.VERSION[0] >= 5:
+    # db_default attribute was only added in Django 5.0
+    INSTALLED_APPS.append(
+        "tests.test_project.app_add_not_null_column_followed_by_db_default"
+    )
+
 MIDDLEWARE = [
     "django.middleware.security.SecurityMiddleware",
     "django.contrib.sessions.middleware.SessionMiddleware",

tests/unit/test_sql_analyser.py

@@ -66,6 +66,15 @@ class MySqlAnalyserTestCase(SqlAnalyserTestCase):
         ]
         self.assertBackwardIncompatibleSql(sql)
 
+    def test_add_not_null_without_dropping_default(self):
+        sql = (
+            "ALTER TABLE `app_add_not_null_column_a` ADD COLUMN `new_not_null_field` integer DEFAULT 1 NOT NULL;",
+        )
+        self.assertValidSql(sql)
+
+        sql = "ALTER TABLE `app_add_not_null_column_followed_by_default_a` ADD COLUMN `not_null_field_db_default` integer DEFAULT (PI()) NOT NULL;"
+        self.assertValidSql(sql)
+
     def test_add_not_null_followed_by_default(self):
         sql = [
             "ALTER TABLE `app_add_not_null_column_followed_by_default_a` ADD COLUMN `new_not_null_field` integer DEFAULT 1 NOT NULL;",
@@ -147,6 +156,15 @@ class SqliteAnalyserTestCase(SqlAnalyserTestCase):
         ]
         self.assertBackwardIncompatibleSql(sql)
 
+    def test_add_not_null_without_dropping_default(self):
+        sql = [
+            'CREATE TABLE "new__app_add_not_null_column_followed_by_default_a" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "not_null_field_db_default" integer DEFAULT (PI()) NOT NULL, "field" integer NOT NULL, "not_null_field" integer NOT NULL);',
+            'INSERT INTO "new__app_add_not_null_column_followed_by_default_a" ("id", "field", "not_null_field") SELECT "id", "field", "not_null_field" FROM "app_add_not_null_column_followed_by_default_a";',
+            'DROP TABLE "app_add_not_null_column_followed_by_default_a";',
+            'ALTER TABLE "new__app_add_not_null_column_followed_by_default_a" RENAME TO "app_add_not_null_column_followed_by_default_a";',
+        ]
+        self.assertBackwardIncompatibleSql(sql)
+
     def test_create_table_with_not_null(self):
         sql = 'CREATE TABLE "app_create_table_with_not_null_column_a" ("id" integer NOT NULL PRIMARY KEY AUTOINCREMENT, "field" varchar(150) NOT NULL);'
         self.assertValidSql(sql)
@@ -207,6 +225,10 @@ class PostgresqlAnalyserTestCase(SqlAnalyserTestCase):
         sql = 'ALTER TABLE "app_alter_column_a" ALTER COLUMN "field" TYPE varchar(10) USING "field"::varchar(10);'
         self.assertBackwardIncompatibleSql(sql)
 
+    def test_add_not_null_without_dropping_default(self):
+        sql = 'ALTER TABLE "app_add_not_null_column_followed_by_default_a" ADD COLUMN "not_null_field_db_default" integer DEFAULT (PI()) NOT NULL;'
+        self.assertValidSql(sql)
+
     def test_not_null_followed_by_default(self):
         sql = [
             'ALTER TABLE "app_add_not_null_column_followed_by_default_a" ADD COLUMN "not_null_field" integer DEFAULT 1 NOT NULL;',