Feature: async default value

CHANGELOG.rst

@@ -16,6 +16,7 @@ Added
 - Enhancement for FastAPI lifespan support (#1371)
 - Add __eq__ method to Q to more easily test dynamically-built queries (#1506)
 - Added PlainToTsQuery function for postgres (#1347)
+- Allow field's default keyword to be async function (#1498)
 
 Fixed
 ^^^^^

tests/test_callable_default.py

@@ -0,0 +1,21 @@
+from tests import testmodels
+from tortoise.contrib import test
+
+
+class TestCallableDefault(test.TestCase):
+    async def test_default_create(self):
+        model = await testmodels.CallableDefault.create()
+        self.assertEqual(model.callable_default, "callable_default")
+        self.assertEqual(model.async_default, "async_callable_default")
+
+    async def test_default_by_save(self):
+        saved_model = testmodels.CallableDefault()
+        await saved_model.save()
+        self.assertEqual(saved_model.callable_default, "callable_default")
+        self.assertEqual(saved_model.async_default, "async_callable_default")
+
+    async def test_async_default_change(self):
+        default_change = testmodels.CallableDefault()
+        default_change.async_default = "changed"
+        await default_change.save()
+        self.assertEqual(default_change.async_default, "changed")

tests/testmodels.py

@@ -892,3 +892,17 @@ class PydanticMeta:
             alias_generator=camelize_var,
             populate_by_name=True,
         )
+
+
+def callable_default() -> str:
+    return "callable_default"
+
+
+async def async_callable_default() -> str:
+    return "async_callable_default"
+
+
+class CallableDefault(Model):
+    id = fields.IntField(pk=True)
+    callable_default = fields.CharField(max_length=32, default=callable_default)
+    async_default = fields.CharField(max_length=32, default=async_callable_default)

tortoise/models.py

@@ -667,15 +667,25 @@ def __init__(self, **kwargs: Any) -> None:
         self._partial = False
         self._saved_in_db = False
         self._custom_generated_pk = False
+        self._await_when_save: Dict[str, Callable[[], Awaitable[Any]]] = {}
 
         # Assign defaults for missing fields
         for key in meta.fields.difference(self._set_kwargs(kwargs)):
             field_object = meta.fields_map[key]
-            if callable(field_object.default):
-                setattr(self, key, field_object.default())
+            field_default = field_object.default
+            if inspect.iscoroutinefunction(field_default):
+                self._await_when_save[key] = field_default
+            elif callable(field_default):
+                setattr(self, key, field_default())
             else:
                 setattr(self, key, deepcopy(field_object.default))
 
+    def __setattr__(self, key, value):
+        # set field value override async default function
+        if hasattr(self, "_await_when_save"):
+            self._await_when_save.pop(key, None)
+        super().__setattr__(key, value)
+
     def _set_kwargs(self, kwargs: dict) -> Set[str]:
         meta = self._meta
 
@@ -719,6 +729,7 @@ def _init_from_db(cls: Type[MODEL], **kwargs: Any) -> MODEL:
         self._partial = False
         self._saved_in_db = True
         self._custom_generated_pk = self._meta.db_pk_column not in self._meta.generated_db_fields
+        self._await_when_save = {}
 
         meta = self._meta
 
@@ -845,6 +856,13 @@ def register_listener(cls, signal: Signals, listener: Callable):
         if listener not in cls_listeners:
             cls_listeners.append(listener)
 
+    async def _set_async_default_field(self) -> None:
+        """retrieve value from field's async default value"""
+        if hasattr(self, "_await_when_save"):
+            for k, v in self._await_when_save.copy().items():
+                setattr(self, k, await v())
+            self._await_when_save = {}
+
     async def _pre_delete(
         self,
         using_db: Optional[BaseDBAsyncClient] = None,
@@ -921,6 +939,7 @@ async def save(
         :raises IncompleteInstanceError: If the model is partial and the fields are not available for persistence.
         :raises IntegrityError: If the model can't be created or updated (specifically if force_create or force_update has been set)
         """
+        await self._set_async_default_field()
         db = using_db or self._choose_db(True)
         executor = db.executor_class(model=self.__class__, db=db)
         if self._partial: