Accept None in the migrations_folder_path argument

piccolo/apps/migrations/commands/base.py

@@ -31,7 +31,7 @@ async def create_migration_table(self) -> bool:
         return False
 
     def get_migration_modules(
-        self, folder_path: str
+        self, folder_path: Optional[str] = None
     ) -> dict[str, MigrationModule]:
         """
         Imports the migration modules in the given folder path, and returns
@@ -40,7 +40,8 @@ def get_migration_modules(
         """
         migration_modules = {}
 
-        sys.path.insert(0, folder_path)
+        if folder_path is not None:
+            sys.path.insert(0, folder_path)
 
         folder_contents = os.listdir(folder_path)
         excluded = ("__init__.py",)

piccolo/apps/migrations/commands/new.py

@@ -98,9 +98,10 @@ def _generate_migration_meta(app_config: AppConfig) -> NewMigrationMeta:
 
     filename = f"{cleaned_app_name}_{cleaned_id}"
 
-    path = os.path.join(
-        app_config.resolved_migrations_folder_path, f"{filename}.py"
-    )
+    if app_config.resolved_migrations_folder_path is not None:
+        path = os.path.join(
+            app_config.resolved_migrations_folder_path, f"{filename}.py"
+        )
 
     return NewMigrationMeta(
         migration_id=_id, migration_filename=filename, migration_path=path
@@ -257,7 +258,10 @@ async def new(
 
         app_config = Finder().get_app_config(app_name=app_name)
 
-        _create_migrations_folder(app_config.resolved_migrations_folder_path)
+        if app_config.resolved_migrations_folder_path:
+            _create_migrations_folder(
+                app_config.resolved_migrations_folder_path
+            )
 
         try:
             await _create_new_migration(

piccolo/conf/apps.py

@@ -182,13 +182,13 @@ class AppConfig:
     """
 
     app_name: str
-    migrations_folder_path: Union[str, pathlib.Path]
+    migrations_folder_path: Union[str, pathlib.Path, None]
     table_classes: list[type[Table]] = field(default_factory=list)
     migration_dependencies: list[str] = field(default_factory=list)
     commands: list[Union[Callable, Command]] = field(default_factory=list)
 
     @property
-    def resolved_migrations_folder_path(self) -> str:
+    def resolved_migrations_folder_path(self) -> Union[str, None]:
         return (
             str(self.migrations_folder_path)
             if isinstance(self.migrations_folder_path, pathlib.Path)

tests/apps/migrations/auto/integration/test_migrations.py

@@ -148,10 +148,11 @@ def _test_migrations(
 
         migrations_folder_path = app_config.resolved_migrations_folder_path
 
-        if os.path.exists(migrations_folder_path):
-            shutil.rmtree(migrations_folder_path)
+        if migrations_folder_path is not None:
+            if os.path.exists(migrations_folder_path):
+                shutil.rmtree(migrations_folder_path)
 
-        _create_migrations_folder(migrations_folder_path)
+            _create_migrations_folder(migrations_folder_path)
 
         for table_snapshot in table_snapshots:
             app_config.table_classes = table_snapshot

tests/conf/test_apps.py

@@ -84,6 +84,13 @@ def test_get_table_with_name(self):
 
 
 class TestAppConfig(TestCase):
+    def test_migrations_folder_path_is_none(self):
+        """
+        Make sure that ``migrations_folder_path`` argument can be ``None``.
+        """
+        config = AppConfig(app_name="music", migrations_folder_path=None)
+        self.assertEqual(config.resolved_migrations_folder_path, None)
+
     def test_pathlib(self):
         """
         Make sure a ``pathlib.Path`` instance can be passed in as a