pre_delete signal not working in specific directory - django

Question

i want remove file from storage when a File instance removed.trying to use django signal. here is my model File:
class File(models.Model):
orig_name = models.CharField(_('Original Name'), max_length=255)
conversation = models.ForeignKey('conversation.Conversation', on_delete=models.CASCADE)
the architecture of every app are same.means all of app have own signals directory and in signals's directory we have __init__.py and handlers.py files .here is a brief tree of my app with some detail for file's app:
apps
├── conversation
├── post
└── file
├── admin.py
├── apps.py
├── __init__.py
├── models.py
├── signals
│   ├── handlers.py
│   └── __init__.py
├── tests.py
├── urls.py
└── views.py
here is apps/file/apps.py:
from django.apps import AppConfig
class FileConfig(AppConfig):
name = 'apps.file' # exact as INSTALLED_APP in setting.py
def ready(self):
import apps.file.signals.handers
here is apps/file/signals/handlers.py :
from django.db.models.signals import pre_delete
from django.dispatch import receiver
from apps.file.models import File
#receiver(pre_delete, sender=File)
def remove_file_from_storage(sender, instance, *args, **kwargs):
print('pre_delete signal for File working')
# some code is here
and app/file/signals/__init__.py file is empty. in this project we are using multiple signals and all of them working fine but i don't know why this signal not working.other signal are from custom and build-in signal both. please notice when i moving def remove_file_from_storage function into other app into related app_name/signals/handlers.py it's working fine.the process of deleting is a simple generics.DestroyAPIView of DRF. where is the problem with my architect of using signal?thank you

Answer 1

The problem is because you use receiver decorator to register signals. With that you have to place your code inside ready function of your Django application. This document does mention about that:
In practice, signal handlers are usually defined in a signals submodule of the application they relate to. Signal receivers are connected in the ready() method of your application configuration class. If you’re using the receiver() decorator, simply import the signals submodule inside ready().
But in real practice, we won't put all signals code inside ready method, that might make our code harder to read and harder to maintain. So like you did, we will put the signals inside signals.py and then load it into your app via ready method, like so:
from django.apps import AppConfig
class FileConfig(AppConfig):
label = 'file'
name = 'file'
def ready(self):
from apps.file import signals # NOQA
# add # NOQA to ignore error message from Python linter when we just import but never used
and set this to __init__.py so that Django could discover your app:
apps
├── conversation
├── post
└── file
├── admin.py
├── apps.py
├── __init__.py # Add to this file
├── models.py
├── signals
│ ├── handlers.py
│ └── __init__.py
├── tests.py
├── urls.py
└── views.py
default_app_config = 'apps.file.apps.FileConfig'
You could also take a look at this article to gain more details about Django signals
Hope that helps!