Make user enrollment more robust

ECOM-1730

common/djangoapps/student/models.py

@@ -1030,32 +1030,14 @@ class CourseEnrollment(models.Model):
         if user.id is None:
             user.save()
 
-        try:
-            enrollment, created = cls.objects.get_or_create(
-                user=user,
-                course_id=course_key,
-            )
-
-            # If we *did* just create a new enrollment, set some defaults
-            if created:
-                enrollment.mode = CourseMode.DEFAULT_MODE_SLUG
-                enrollment.is_active = False
-                enrollment.save()
-
-        except IntegrityError:
-            log.info(
-                (
-                    "An integrity error occurred while getting-or-creating the enrollment"
-                    "for course key %s and student %s. This can occur if two processes try to get-or-create "
-                    "the enrollment at the same time and the database is set to REPEATABLE READ. We will try "
-                    "committing the transaction and retrying."
-                ),
-                course_key, user
-            )
-            enrollment = cls.objects.get(
-                user=user,
-                course_id=course_key,
-            )
+        enrollment, __ = cls.objects.get_or_create(
+            user=user,
+            course_id=course_key,
+            defaults={
+                'mode': CourseMode.DEFAULT_MODE_SLUG,
+                'is_active': False
+            }
+        )
 
         return enrollment
 

common/djangoapps/student/tests/test_enrollment.py

@@ -8,7 +8,6 @@ from nose.plugins.attrib import attr
 
 from django.conf import settings
 from django.core.urlresolvers import reverse
-from django.db import IntegrityError
 from course_modes.models import CourseMode
 from xmodule.modulestore.tests.django_utils import SharedModuleStoreTestCase
 from xmodule.modulestore.tests.factories import CourseFactory
@@ -282,18 +281,3 @@ class EnrollmentTest(UrlResetMixin, SharedModuleStoreTestCase):
             params['email_opt_in'] = email_opt_in
 
         return self.client.post(reverse('change_enrollment'), params)
-
-    def test_get_or_create_integrity_error(self):
-        """Verify that get_or_create_enrollment handles IntegrityError."""
-
-        CourseEnrollmentFactory.create(user=self.user, course_id=self.course.id)
-
-        with patch.object(CourseEnrollment.objects, "get_or_create") as mock_get_or_create:
-            mock_get_or_create.side_effect = IntegrityError
-            enrollment = CourseEnrollment.get_or_create_enrollment(
-                self.user,
-                self.course.id
-            )
-
-        self.assertEqual(enrollment.user, self.user)
-        self.assertEqual(enrollment.course.id, self.course.id)