I needed to bulk-delete a large number of objects today. Django deletions are relatively inefficient by default, because Django implements its own version of cascading deletions and fires signals for each deleted object.
\nI knew that I wanted to avoid both of these and run a bulk DELETE SQL operation.
Django has an undocumented queryset._raw_delete(db_connection) method that can do this:
reports_qs = Report.objects.filter(public_id__in=report_ids)\nreports_qs._raw_delete(reports_qs.db)But this failed for me, because my Report object has a many-to-many relationship with another table - and those records were not deleted.
I could have hand-crafted a PostgreSQL cascading delete here, but I instead decided to manually delete those many-to-many records first. Here's what that looked like:
\nreport_availability_tag_qs = (\n Report.availability_tags.through.objects.filter(\n report__public_id__in=report_ids\n )\n)\nreport_availability_tag_qs._raw_delete(report_availability_tag_qs.db)This didn't quite work either, because I have another model Location with foreign key references to those reports. So I added this:
Location.objects.filter(latest_report__public_id__in=report_ids).update(\n latest_report=None\n)That combination worked! The Django debug toolbar confirmed that this executed one UPDATE followed by two efficient bulk DELETE operations.