Fix cascading special coverage deletion

bulbs/special_coverage/migrations/0003_auto_20150423_2007.py

@@ -0,0 +1,21 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import models, migrations
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('special_coverage', '0002_auto_20150318_2110'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='specialcoverage',
+            name='campaign',
+            field=models.ForeignKey(on_delete=django.db.models.deletion.SET_NULL, default=None, blank=True, to='campaigns.Campaign', null=True),
+            preserve_default=True,
+        ),
+    ]

bulbs/special_coverage/models.py

@@ -21,7 +21,8 @@ class SpecialCoverage(models.Model):
     videos = JSONField(default=[], blank=True)
     active = models.BooleanField(default=False)
     promoted = models.BooleanField(default=False)
-    campaign = models.ForeignKey(Campaign, null=True, default=None, blank=True)
+    campaign = models.ForeignKey(
+        Campaign, null=True, default=None, blank=True, on_delete=models.SET_NULL)
 
     def __unicode__(self):
         return self.name