From 6f524ce2239ee40eac41b066adc9c4dc3febe542 Mon Sep 17 00:00:00 2001
From: Guruprasad Lakshmi Narayanan <guruprasad@opencraft.com>
Date: Fri, 19 Jul 2019 18:43:17 +0530
Subject: [PATCH] Use a callable as the default value for CourseEnrollment.mode

The previous behaviour of using a variable causes Django to complain
about changes not reflected in a migration when the default course
mode slug is changed.
---
 common/djangoapps/course_modes/models.py      |  8 ++++++
 ..._courseenrollment_mode_callable_default.py | 26 +++++++++++++++++++
 common/djangoapps/student/models.py           |  2 +-
 3 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 common/djangoapps/student/migrations/0027_courseenrollment_mode_callable_default.py

diff --git a/common/djangoapps/course_modes/models.py b/common/djangoapps/course_modes/models.py
index e967fe3f16..0bd8a1f6d6 100644
--- a/common/djangoapps/course_modes/models.py
+++ b/common/djangoapps/course_modes/models.py
@@ -255,6 +255,14 @@ class CourseMode(models.Model):
             self.expiration_datetime_is_explicit = True
         self._expiration_datetime = new_datetime
 
+    @classmethod
+    def get_default_mode_slug(cls):
+        """
+        Returns the default mode slug to be used in the CourseEnrollment model mode field
+        as the default value.
+        """
+        return cls.DEFAULT_MODE_SLUG
+
     @classmethod
     def all_modes_for_courses(cls, course_id_list):
         """Find all modes for a list of course IDs, including expired modes.
diff --git a/common/djangoapps/student/migrations/0027_courseenrollment_mode_callable_default.py b/common/djangoapps/student/migrations/0027_courseenrollment_mode_callable_default.py
new file mode 100644
index 0000000000..77caab9e59
--- /dev/null
+++ b/common/djangoapps/student/migrations/0027_courseenrollment_mode_callable_default.py
@@ -0,0 +1,26 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.22 on 2019-07-19 13:06
+from __future__ import unicode_literals
+
+import course_modes.models
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('student', '0026_allowedauthuser'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='courseenrollment',
+            name='mode',
+            field=models.CharField(default=course_modes.models.CourseMode.get_default_mode_slug, max_length=100),
+        ),
+        migrations.AlterField(
+            model_name='historicalcourseenrollment',
+            name='mode',
+            field=models.CharField(default=course_modes.models.CourseMode.get_default_mode_slug, max_length=100),
+        ),
+    ]
diff --git a/common/djangoapps/student/models.py b/common/djangoapps/student/models.py
index 58bd592bb0..1795d1f127 100644
--- a/common/djangoapps/student/models.py
+++ b/common/djangoapps/student/models.py
@@ -1101,7 +1101,7 @@ class CourseEnrollment(models.Model):
 
     # Represents the modes that are possible. We'll update this later with a
     # list of possible values.
-    mode = models.CharField(default=CourseMode.DEFAULT_MODE_SLUG, max_length=100)
+    mode = models.CharField(default=CourseMode.get_default_mode_slug, max_length=100)
 
     # An audit row will be created for every change to a CourseEnrollment. This
     # will create a new model behind the scenes - HistoricalCourseEnrollment and a