Replace backfillchannels with a data migration

hc/api/management/commands/backfillchannels.py

@@ -1,24 +0,0 @@
-from django.core.management.base import BaseCommand
-
-from hc.api.models import Channel, Notification
-
-
-class Command(BaseCommand):
-    help = "Backfill Channel.last_notify and Channel.last_error"
-
-    def handle(self, *args, **options):
-        total = 0
-
-        for channel in Channel.objects.all():
-            q = Channel.objects.filter(id=channel.id)
-
-            try:
-                n = Notification.objects.filter(channel=channel).latest()
-                q.update(last_notify=n.created, last_error=n.error)
-                total += 1
-            except Notification.DoesNotExist:
-                if channel.last_error:
-                    q.update(last_error="")
-                    total += 1
-
-        return "Done! Updated %d channels." % total

hc/api/migrations/0082_fill_last_notify.py

@@ -0,0 +1,24 @@
+# Generated by Django 3.2.8 on 2021-10-21 09:30
+
+from django.db import migrations
+
+
+def fill_last_notify(apps, schema_editor):
+    Channel = apps.get_model("api", "Channel")
+    Notification = apps.get_model("api", "Notification")
+    for channel in Channel.objects.filter(last_notify=None):
+        try:
+            n = Notification.objects.filter(channel=channel).latest()
+            channel.last_notify = n.created
+            channel.save()
+        except Notification.DoesNotExist:
+            pass
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("api", "0081_channel_last_notify"),
+    ]
+
+    operations = [migrations.RunPython(fill_last_notify, migrations.RunPython.noop)]