Fix for schedule delete 500 from Gabe (#4290)

awx/main/migrations/0115_v370_schedule_set_null.py

@@ -0,0 +1,24 @@
+# Generated by Django 2.2.11 on 2020-05-04 02:26
+
+import awx.main.utils.polymorphic
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('main', '0114_v370_remove_deprecated_manual_inventory_sources'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='unifiedjob',
+            name='schedule',
+            field=models.ForeignKey(default=None, editable=False, null=True, on_delete=awx.main.utils.polymorphic.SET_NULL, to='main.Schedule'),
+        ),
+        migrations.AlterField(
+            model_name='unifiedjobtemplate',
+            name='next_schedule',
+            field=models.ForeignKey(default=None, editable=False, null=True, on_delete=awx.main.utils.polymorphic.SET_NULL, related_name='unifiedjobtemplate_as_next_schedule+', to='main.Schedule'),
+        ),
+    ]

awx/main/models/unified_jobs.py

@@ -150,7 +150,7 @@ class UnifiedJobTemplate(PolymorphicModel, CommonModelNameNotUnique, Notificatio
         default=None,
         editable=False,
         related_name='%(class)s_as_next_schedule+',
-        on_delete=models.SET_NULL,
+        on_delete=polymorphic.SET_NULL,
     )
     status = models.CharField(
         max_length=32,
@@ -587,7 +587,7 @@ class UnifiedJob(PolymorphicModel, PasswordFieldsModel, CommonModelNameNotUnique
         null=True,
         default=None,
         editable=False,
-        on_delete=models.SET_NULL,
+        on_delete=polymorphic.SET_NULL,
     )
     dependent_jobs = models.ManyToManyField(
         'self',