Custom one-to-one field for ref to custom id field

lms/djangoapps/coursewarehistoryextended/fields.py

@@ -3,6 +3,7 @@ Custom fields for use in the coursewarehistoryextended django app.
 """
 
 from django.db.models.fields import AutoField
+from django.db.models.fields.related import OneToOneField
 
 
 class UnsignedBigIntAutoField(AutoField):
@@ -24,6 +25,7 @@ class UnsignedBigIntAutoField(AutoField):
         else:
             return None
 
+    # rel_db_type was added in Django 1.10. For versions before, use UnsignedBigIntOneToOneField.
     def rel_db_type(self, connection):
         if connection.settings_dict['ENGINE'] == 'django.db.backends.mysql':
             return "bigint UNSIGNED"
@@ -33,3 +35,20 @@ class UnsignedBigIntAutoField(AutoField):
             return "BIGSERIAL"
         else:
             return None
+
+
+class UnsignedBigIntOneToOneField(OneToOneField):
+    """
+    An unsigned 8-byte integer one-to-one foreign key to a unsigned 8-byte integer id field.
+
+    Should only be necessary for versions of Django < 1.10.
+    """
+    def db_type(self, connection):
+        if connection.settings_dict['ENGINE'] == 'django.db.backends.mysql':
+            return "bigint UNSIGNED"
+        elif connection.settings_dict['ENGINE'] == 'django.db.backends.sqlite3':
+            return "integer"
+        elif connection.settings_dict['ENGINE'] == 'django.db.backends.postgresql_psycopg2':
+            return "BIGSERIAL"
+        else:
+            return None

lms/djangoapps/grades/migrations/0013_persistentsubsectiongradeoverride.py

@@ -3,6 +3,8 @@ from __future__ import unicode_literals
 
 from django.db import migrations, models
 
+from coursewarehistoryextended.fields import UnsignedBigIntOneToOneField
+
 
 class Migration(migrations.Migration):
 
@@ -21,7 +23,7 @@ class Migration(migrations.Migration):
                 ('possible_all_override', models.FloatField(null=True, blank=True)),
                 ('earned_graded_override', models.FloatField(null=True, blank=True)),
                 ('possible_graded_override', models.FloatField(null=True, blank=True)),
-                ('grade', models.OneToOneField(related_name='override', to='grades.PersistentSubsectionGrade')),
+                ('grade', UnsignedBigIntOneToOneField(related_name='override', to='grades.PersistentSubsectionGrade')),
             ],
         ),
     ]

lms/djangoapps/grades/models.py

@@ -20,7 +20,7 @@ from lazy import lazy
 from model_utils.models import TimeStampedModel
 from opaque_keys.edx.keys import CourseKey, UsageKey
 
-from coursewarehistoryextended.fields import UnsignedBigIntAutoField
+from coursewarehistoryextended.fields import UnsignedBigIntAutoField, UnsignedBigIntOneToOneField
 from eventtracking import tracker
 from openedx.core.djangoapps.xmodule_django.models import CourseKeyField, UsageKeyField
 from request_cache import get_cache
@@ -693,7 +693,7 @@ class PersistentSubsectionGradeOverride(models.Model):
     class Meta(object):
         app_label = "grades"
 
-    grade = models.OneToOneField(PersistentSubsectionGrade, related_name='override')
+    grade = UnsignedBigIntOneToOneField(PersistentSubsectionGrade, related_name='override')
 
     # Created/modified timestamps prevent race-conditions when using with async rescoring tasks
     created = models.DateTimeField(auto_now_add=True, db_index=True)