Django management command to wipe all traces of a django app with models from DB

remove_django_app.py

"""
Completely remove all traces of a django app from the DB.

Suggested workflow:

Step 1: carefully remove dependencies on app from code base

Step 2: run this command to remove all traces of app model instances and content types from DB

Step 3: deploy code changes and this command everywhere (e.g., on stage and production codebase and DB)

At some future date...

Step 4: remove app from settings.INSTALLED_APPS
        remove app code from codebase

Step 5: deploy new codebase everywhere

"""
from django.contrib.contenttypes.models import ContentType
from django.contrib.auth.models import Permission
from django.contrib.admin.models import LogEntry
from django.core.management import call_command
from django.core.management.base import BaseCommand


def confirm(question, default=None):
    result = input("%s (y/n): " % question)
    if not result and default is not None:
        return default
    while len(result) < 1 or result[0].lower() not in "yn":
        result = input("Please answer yes or no: ")
    return result[0].lower() == "y"


class Command(BaseCommand ):
    help = "Completely wipe app from the DB."

    def add_arguments(self, parser):
        parser.add_argument('--quiet', action='store_true', help='suppress verbose output')
        parser.add_argument('app_label', default=None, help='app label of app to remove.')

    def instructions(self):
        self.stdout.write("CAUTION: this command will completely remove all traces of the app from the DB.")
        self.stdout.write(" Before starting...")
        self.stdout.write("    - ensure all dependencies on the app have been removed from code base;")
        self.stdout.write("    - carefully check for any remaining DB relations to the app models;")
        self.stdout.write("    - check for and eliminate any migration dependencies on the app;")
        self.stdout.write("    - otherwise, leave app installed and code intact (at least apps, models, and migrations);")

    def handle(self, *args, **options):
        app_label = options['app_label']
        quiet = options.get('quiet', False)
        if not quiet:
            self.instructions()

        if confirm(f'Proceed with removing {app_label}? ', default='n'):
            self.remove_app(app_label, quiet)
        elif not quiet:
            self.stdout.write(" Operation aborted.  No changes made.")

    def remove_app(self, app_label, quiet=False):
        """ Completely wipe all traces of app_label app from DB """
        # pre-fetch all objects related to the app's content types
        #   perms will cascade, but delete them first so whole op. can be in DB
        content_types = ContentType.objects.filter(app_label=app_label).all()
        permissions = Permission.objects.filter(content_type_id__in=content_types)
        log_entries = LogEntry.objects.filter(content_type_id__in=content_types)

        if not quiet:
            self.stdout.write(f'Removing all traces of {app_label}, including...')
            self.stdout.write(f'  {content_types.count()} ContentType :')
            self.stdout.write(f'     {[c.model for c in content_types]}')
            self.stdout.write(f'  {permissions.count()} Permission :')
            self.stdout.write(f'     {[p.codename for p in permissions]}')
            self.stdout.write(f'  {log_entries.count()} LogEntry :')
            self.stdout.write(f'     {[l.change_message for l in log_entries]}')

        go = confirm(f'run `> migrate {app_label} zero`; and delete related content type data?', default='n')

        if go:
            # reverse migrations to remove model DB tables and migrations entries
            call_command('migrate', app_label, 'zero')
            # delete the content type related data
            log_entries.delete()
            permissions.delete()
            content_types.delete()
            if not quiet:
                self.stdout.write(f'{app_label} successfully removed.')
                self.stdout.write(f'Next steps:  deploy this change everywhere; then remove app code at some future date.')
        elif not quiet:
            self.stdout.write(" Operation aborted.  No changes made.")