MA-1036 Make CourseOverviews handle malformed grading policies

openedx/core/djangoapps/content/course_overviews/migrations/0004_default_lowest_passing_grade_to_None.py

+# -*- coding: utf-8 -*-
+from south.utils import datetime_utils as datetime
+from south.db import db
+from south.v2 import SchemaMigration
+from django.db import models
+
+
+class Migration(SchemaMigration):
+
+    def forwards(self, orm):
+
+        # Changing field 'CourseOverview.lowest_passing_grade'
+        db.alter_column('course_overviews_courseoverview', 'lowest_passing_grade', self.gf('django.db.models.fields.DecimalField')(null=True, max_digits=5, decimal_places=2))
+
+    def backwards(self, orm):
+
+        # Changing field 'CourseOverview.lowest_passing_grade'
+        db.alter_column('course_overviews_courseoverview', 'lowest_passing_grade', self.gf('django.db.models.fields.DecimalField')(default=0.5, max_digits=5, decimal_places=2))
+
+    models = {
+        'course_overviews.courseoverview': {
+            'Meta': {'object_name': 'CourseOverview'},
+            '_location': ('xmodule_django.models.UsageKeyField', [], {'max_length': '255'}),
+            '_pre_requisite_courses_json': ('django.db.models.fields.TextField', [], {}),
+            'advertised_start': ('django.db.models.fields.TextField', [], {'null': 'True'}),
+            'cert_html_view_enabled': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'cert_name_long': ('django.db.models.fields.TextField', [], {}),
+            'cert_name_short': ('django.db.models.fields.TextField', [], {}),
+            'certificates_display_behavior': ('django.db.models.fields.TextField', [], {'null': 'True'}),
+            'certificates_show_before_end': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'course_image_url': ('django.db.models.fields.TextField', [], {}),
+            'days_early_for_beta': ('django.db.models.fields.FloatField', [], {'null': 'True'}),
+            'display_name': ('django.db.models.fields.TextField', [], {'null': 'True'}),
+            'display_number_with_default': ('django.db.models.fields.TextField', [], {}),
+            'display_org_with_default': ('django.db.models.fields.TextField', [], {}),
+            'end': ('django.db.models.fields.DateTimeField', [], {'null': 'True'}),
+            'end_of_course_survey_url': ('django.db.models.fields.TextField', [], {'null': 'True'}),
+            'facebook_url': ('django.db.models.fields.TextField', [], {'null': 'True'}),
+            'has_any_active_web_certificate': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'id': ('xmodule_django.models.CourseKeyField', [], {'max_length': '255', 'primary_key': 'True', 'db_index': 'True'}),
+            'lowest_passing_grade': ('django.db.models.fields.DecimalField', [], {'null': 'True', 'max_digits': '5', 'decimal_places': '2'}),
+            'mobile_available': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'social_sharing_url': ('django.db.models.fields.TextField', [], {'null': 'True'}),
+            'start': ('django.db.models.fields.DateTimeField', [], {'null': 'True'}),
+            'visible_to_staff_only': ('django.db.models.fields.BooleanField', [], {'default': 'False'})
+        }
+    }
+
+    complete_apps = ['course_overviews']
\ No newline at end of file

openedx/core/djangoapps/content/course_overviews/models.py

@@ -52,7 +52,7 @@ class CourseOverview(django.db.models.Model):
     cert_name_long = TextField()
 
     # Grading
-    lowest_passing_grade = DecimalField(max_digits=5, decimal_places=2)
+    lowest_passing_grade = DecimalField(max_digits=5, decimal_places=2, null=True)
 
     # Access parameters
     days_early_for_beta = FloatField(null=True)
@@ -77,6 +77,16 @@ class CourseOverview(django.db.models.Model):
         from lms.djangoapps.certificates.api import get_active_web_certificate
         from lms.djangoapps.courseware.courses import course_image_url
 
+        # Workaround for a problem discovered in https://openedx.atlassian.net/browse/TNL-2806.
+        # If the course has a malformed grading policy such that
+        # course._grading_policy['GRADE_CUTOFFS'] = {}, then
+        # course.lowest_passing_grade will raise a ValueError.
+        # Work around this for now by defaulting to None.
+        try:
+            lowest_passing_grade = course.lowest_passing_grade
+        except ValueError:
+            lowest_passing_grade = None
+
         return CourseOverview(
             id=course.id,
             _location=course.location,
@@ -98,7 +108,7 @@ class CourseOverview(django.db.models.Model):
             has_any_active_web_certificate=(get_active_web_certificate(course) is not None),
             cert_name_short=course.cert_name_short,
             cert_name_long=course.cert_name_long,
-            lowest_passing_grade=course.lowest_passing_grade,
+            lowest_passing_grade=lowest_passing_grade,
             end_of_course_survey_url=course.end_of_course_survey_url,
 
             days_early_for_beta=course.days_early_for_beta,

openedx/core/djangoapps/content/course_overviews/tests.py

@@ -294,3 +294,18 @@ class CourseOverviewTestCase(ModuleStoreTestCase):
             # which causes get_from_id to raise an IOError.
             with self.assertRaises(IOError):
                 CourseOverview.get_from_id(course.id)
+
+    def test_malformed_grading_policy(self):
+        """
+        Test that CourseOverview handles courses with a malformed grading policy
+        such that course._grading_policy['GRADE_CUTOFFS'] = {} by defaulting
+        .lowest_passing_grade to None.
+
+        Created in response to https://openedx.atlassian.net/browse/TNL-2806.
+        """
+        course = CourseFactory.create()
+        course._grading_policy['GRADE_CUTOFFS'] = {}  # pylint: disable=protected-access
+        with self.assertRaises(ValueError):
+            __ = course.lowest_passing_grade
+        course_overview = CourseOverview._create_from_course(course)  # pylint: disable=protected-access
+        self.assertEqual(course_overview.lowest_passing_grade, None)