added option to generate empty migration file

aerich/__init__.py

@@ -123,8 +123,8 @@ class Command:
         inspect = cls(connection, tables)
         return await inspect.inspect()
 
-    async def migrate(self, name: str = "update"):
+    async def migrate(self, name: str = "update", empty: bool = False) -> str:
-        return await Migrate.migrate(name)
+        return await Migrate.migrate(name, empty)
 
     async def init_db(self, safe: bool):
         location = self.location

aerich/migrate.py

@@ -130,12 +130,16 @@ class Migrate:
         return version
 
     @classmethod
-    async def migrate(cls, name) -> str:
+    async def migrate(cls, name: str, empty: bool) -> str:
         """
         diff old models and new models to generate diff content
-        :param name:
+        :param name: str name for migration
+        :param empty: bool if True generates empty migration
         :return:
         """
+        if empty:
+            return await cls._generate_diff_py(name)
+
         new_version_content = get_models_describe(cls.app)
         cls.diff_models(cls._last_version_content, new_version_content)
         cls.diff_models(new_version_content, cls._last_version_content, False)

tests/test_migrate.py

@@ -1,3 +1,6 @@
+import tempfile
+from pathlib import Path
+
 import pytest
 from pytest_mock import MockerFixture
 
@@ -5,7 +8,7 @@ from aerich.ddl.mysql import MysqlDDL
 from aerich.ddl.postgres import PostgresDDL
 from aerich.ddl.sqlite import SqliteDDL
 from aerich.exceptions import NotSupportError
-from aerich.migrate import Migrate
+from aerich.migrate import MIGRATE_TEMPLATE, Migrate
 from aerich.utils import get_models_describe
 
 old_models_describe = {
@@ -966,3 +969,15 @@ def test_sort_all_version_files(mocker):
         "10_datetime_update.py",
         "11_datetime_update.py",
     ]
+
+async def test_empty_migration(mocker) -> None:
+    mocker.patch("os.listdir", return_value=[])
+    Migrate.app = "foo"
+    expected_content = MIGRATE_TEMPLATE.format(upgrade_sql=";", downgrade_sql=";")
+    with tempfile.TemporaryDirectory() as temp_dir:
+        Migrate.migrate_location = temp_dir
+
+        migration_file = await Migrate.migrate("update", True)
+
+        with open(Path(temp_dir, migration_file), "r") as f:
+            assert f.read() == expected_content