added migration

edx_proctoring/migrations/0004_auto_20160201_0523.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('edx_proctoring', '0003_auto_20160101_0525'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='proctoredexamsoftwaresecurereview',
+            name='attempt_code',
+            field=models.CharField(unique=True, max_length=255, db_index=True),
+        ),
+    ]

edx_proctoring/models.py

@@ -857,7 +857,7 @@ class ProctoredExamSoftwareSecureReview(TimeStampedModel):
     """
 
     # which student attempt is this feedback for?
-    attempt_code = models.CharField(max_length=255, db_index=True)
+    attempt_code = models.CharField(max_length=255, db_index=True, unique=True)
 
     # overall status of the review
     review_status = models.CharField(max_length=255)