#35869: Add explicit warning when AppConfig.create() can't choose from multiple
subclasses of AppConfig
-------------------------------------+-------------------------------------
Reporter: narasux | Type:
| Cleanup/optimization
Status: new | Component: Core
| (Other)
Version: 5.0 | Severity: Normal
Keywords: AppConfig | Triage Stage:
| Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
When I upgraded my Django project from 3.2 to 4.2, I found that the
`ready` method in my custom AppConfig was never executed.
Example Code:
{{{
# apps/demo/__init__.py
default_app_config = "apps.demo.CustomAppConfig"
}}}
{{{
# apps/demo/apps.py
from django.apps import AppConfig
class PlugableAppConfig(AppConfig):
def ready(self):
# do something...
class CustomAppConfig(PlugableAppConfig):
name = "apps.demo"
def ready(self):
super().ready()
# do something...
}}}
After debugging, reading
[https://docs.djangoproject.com/en/4.2/ref/applications/#configuring-
applications documentation], and comparing version code, I determined that
the reason was that Django 3.2 added support for
[https://github.com/django/django/commit/3f2821af6bc48fa8e7970c1ce27bc54c3172545e
automatic detection for AppConfig] to replace `default_app_config`, and
support for the latter was
[https://github.com/django/django/commit/75d6c4ae6df93c4c4d8621aced3a180afa18a6cb
completely removed in version 4.1].
This is a great new feature, but if there are **multiple subclasses** of
AppConfig in apps.py and none of them specify `default` as `True` (legacy
code), `AppConfig.create()` will default to using the Base AppConfig
[https://github.com/django/django/blob/43287cbb87bc5e99a2fd384082a719d8b4d253c6/django/apps/config.py#L155
without any explicit warning].
This could lead to additional troubleshooting costs for developers.
Therefore, I suggest that when `AppConfig.create()` cannot choose among
multiple subclasses of AppConfig and defaults to using the Base AppConfig,
a warning should be raised to alert developers.
--
Ticket URL: <https://code.djangoproject.com/ticket/35869>
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