zulip/zerver/migrations/0074_fix_duplicate_attachme...

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# -*- coding: utf-8 -*-
# Generated by Django 1.10.5 on 2017-04-13 22:12
from django.db import migrations
from django.db.backends.postgresql_psycopg2.schema import DatabaseSchemaEditor
from django.db.migrations.state import StateApps
from django.db.models import Count
def fix_duplicate_attachments(apps, schema_editor):
# type: (StateApps, DatabaseSchemaEditor) -> None
"""Migration 0041 had a bug, where if multiple messages referenced the
same attachment, rather than creating a single attachment object
for all of them, we would incorrectly create one for each message.
This results in exceptions looking up the Attachment object
corresponding to a file that was used in multiple messages that
predate migration 0041.
This migration fixes this by removing the duplicates, moving their
messages onto a single canonical Attachment object (per path_id).
"""
Attachment = apps.get_model('zerver', 'Attachment')
# Loop through all groups of Attachment objects with the same `path_id`
for group in Attachment.objects.values('path_id').annotate(Count('id')).order_by().filter(id__count__gt=1):
# Sort by the minimum message ID, to find the first attachment
attachments = sorted(list(Attachment.objects.filter(path_id=group['path_id']).order_by("id")),
key = lambda x: min(x.messages.all().values_list('id')[0]))
surviving = attachments[0]
to_cleanup = attachments[1:]
for a in to_cleanup:
# For each duplicate attachment, we transfer its messages
# to the canonical attachment object for that path, and
# then delete the original attachment.
for msg in a.messages.all():
surviving.messages.add(msg)
surviving.is_realm_public = surviving.is_realm_public or a.is_realm_public
surviving.save()
a.delete()
class Migration(migrations.Migration):
dependencies = [
('zerver', '0073_custom_profile_fields'),
]
operations = [
migrations.RunPython(fix_duplicate_attachments)
]