How to run a function at startup before requests are handled in Django?

Question

I want to run some code when my Django server starts-up in order to clean up from the previous end of the server. How can I run some code once and only once at startup before the server processes any requests. I need to access the database during this time.

I've read a couple of things online that seem a bit outdated and are also not guaranteed to run only once.

Update

I've looked at the suggested answer by looking into the ready function. That appears to work, but it is documented that you should not access the database there (https://docs.djangoproject.com/en/dev/ref/applications/#django.apps.AppConfig.ready)

There are many suggestions at Execute code when Django starts ONCE only?, but since that post is a few years old, I thought there might be some additional solutions.

This looks promising

from django.dispatch import receiver
from django.db.backends.signals import connection_created

@receiver(connection_created)
def my_receiver(connection, **kwargs):
    with connection.cursor() as cursor:
        # do something to the database

    connection_created.disconnect(my_receiver)

Any other thoughts?

Answer 1

This is often done with the .ready() method ^[Django-doc] of any of the AppConfig classes ^[Django-doc] of an installed app. So if you have an app named app_name, you can work with:

# app_name/apps.py

from django.apps import AppConfig


class MyAppConfig(AppConfig):
    # …

    def ready(self):
        # my management command
        # …

This will run after the models of all INSTALLED_APPS are loaded, so you can do management commands. This is also often used to hook signals to models.