Fix certificates API for old deleted XML course certificates.

Certificates API is retuning 500 error for old XML courses in which learners
have a valid certificate.

PROD-1247

lms/djangoapps/certificates/apis/v0/tests/test_views.py

@@ -384,3 +384,29 @@ class CertificatesListRestApiTest(AuthAndScopesTestMixin, SharedModuleStoreTestC
         kwargs = {"certificate_uuid": self.cert.verify_uuid}
         expected_download_url = reverse('certificates:render_cert_by_uuid', kwargs=kwargs)
         self.assert_success_response_for_student(response, download_url=expected_download_url)
+
+    @patch('lms.djangoapps.certificates.apis.v0.views.get_course_run_details')
+    def test_certificate_without_course(self, mock_get_course_run_details):
+        """
+        Verify that certificates are returned for deleted XML courses.
+        """
+        expected_course_name = 'Test Course Title'
+        mock_get_course_run_details.return_value = {'title': expected_course_name}
+        xml_course_key = self.store.make_course_key('edX', 'testDeletedCourse', '2020')
+        cert_for_deleted_course = GeneratedCertificateFactory.create(
+            user=self.student,
+            course_id=xml_course_key,
+            status=CertificateStatuses.downloadable,
+            mode='honor',
+            download_url='www.edx.org/honor-cert-for-deleted-course.pdf',
+            grade="0.88"
+        )
+
+        response = self.get_response(
+            AuthType.jwt,
+            requesting_user=self.student,
+            requested_user=self.student,
+        )
+        self.assertEqual(response.status_code, status.HTTP_200_OK)
+        self.assertContains(response, cert_for_deleted_course.download_url)
+        self.assertContains(response, expected_course_name)

lms/djangoapps/certificates/apis/v0/views.py

@@ -18,6 +18,7 @@ from rest_framework.permissions import IsAuthenticated
 from rest_framework.response import Response
 
 from lms.djangoapps.certificates.api import get_certificate_for_user, get_certificates_for_user
+from openedx.core.djangoapps.catalog.utils import get_course_run_details
 from openedx.core.djangoapps.certificates.api import certificates_viewable_for_course
 from openedx.core.djangoapps.content.course_overviews.models import CourseOverview
 from openedx.core.djangoapps.user_api.accounts.api import visible_fields
@@ -270,14 +271,32 @@ class CertificatesListView(APIView):
         for course_key, course_overview in CourseOverview.get_from_ids(
             list(passing_certificates.keys())
         ).items():
+            if not course_overview:
+                # For deleted XML courses in which learners have a valid certificate.
+                # i.e. MITx/7.00x/2013_Spring
+                course_overview = self._get_pseudo_course_overview(course_key)
             if certificates_viewable_for_course(course_overview):
                 course_certificate = passing_certificates[course_key]
                 # add certificate into viewable certificate list only if it's a PDF certificate
                 # or there is an active certificate configuration.
                 if course_certificate['is_pdf_certificate'] or course_overview.has_any_active_web_certificate:
-                    course_certificate['course_display_name'] = course_overview.display_name_with_default
+                    course_display_name = course_overview.display_name
+                    if not course_overview.pk:
+                        course_display_name = course_overview.display_name_with_default
+                    course_certificate['course_display_name'] = course_display_name
                     course_certificate['course_organization'] = course_overview.display_org_with_default
                     viewable_certificates.append(course_certificate)
 
         viewable_certificates.sort(key=lambda certificate: certificate['created'])
         return viewable_certificates
+
+    def _get_pseudo_course_overview(self, course_key):
+        """
+        Returns a pseudo course overview object for deleted courses.
+        """
+        course_run = get_course_run_details(course_key, ['title'])
+        return CourseOverview(
+            display_name=course_run.get('title'),
+            display_org_with_default=course_key.org,
+            certificates_show_before_end=True
+        )