Fix auto_now field not updated with save(update_fields=[...])

tests/test_update.py

@@ -165,6 +165,28 @@ async def test_update_auto_now(db):
     assert obj1.updated_at.date() == updated_at.date()
 
 
+@pytest.mark.asyncio
+async def test_update_auto_now_with_update_fields(db):
+    tournament = await Tournament.create(name="1")
+    event = await Event.create(name="original", tournament=tournament)
+    original_modified = event.modified
+
+    # Set modified to the past so we can detect if it gets updated
+    past = timezone.now() - timedelta(days=1)
+    await Event.filter(pk=event.pk).update(modified=past)
+
+    event = await Event.get(pk=event.pk)
+    assert event.modified.date() == past.date()
+
+    # Update only name with update_fields; auto_now field should also be updated
+    event.name = "updated"
+    await event.save(update_fields=["name"])
+
+    event = await Event.get(pk=event.pk)
+    assert event.name == "updated"
+    assert event.modified.date() == timezone.now().date()
+
+
 @pytest.mark.asyncio
 async def test_update_relation(db):
     tournament_first = await Tournament.create(name="1")

tortoise/models.py

@@ -1149,6 +1149,12 @@ async def save(
                 raise IncompleteInstanceError(
                     f"{self.__class__.__name__} is a partial model, can only be saved with the relevant update_field provided"
                 )
+        if update_fields:
+            update_fields = list(update_fields)
+            for field_name, field_obj in self._meta.fields_map.items():
+                if field_name not in update_fields and getattr(field_obj, "auto_now", False):
+                    update_fields.append(field_name)
+
         await self._pre_save(db, update_fields)
 
         if force_create: