fix: allow non-Elasticsearch search engines when reindexing courses [FC-0062] (openedx#35743)

(cherry picked from commit 689feba)

Author: pomegranited

cms/djangoapps/contentstore/courseware_index.py

@@ -256,7 +256,8 @@ def prepare_item_index(item, skip_index=False, groups_usage_info=None):
                 # Now index the content
                 for item in structure.get_children():
                     prepare_item_index(item, groups_usage_info=groups_usage_info)
-                searcher.index(items_index, request_timeout=timeout)
+                if items_index:
+                    searcher.index(items_index, request_timeout=timeout)
                 cls.remove_deleted_items(searcher, structure_key, indexed_items)
         except Exception as err:  # pylint: disable=broad-except
             # broad exception so that index operation does not prevent the rest of the application from working

cms/djangoapps/contentstore/management/commands/reindex_course.py

@@ -97,14 +97,16 @@ def handle(self, *args, **options):  # pylint: disable=too-many-statements
                         logging.exception('Search Engine error - %s', exc)
                         return
 
-                    index_exists = searcher._es.indices.exists(index=index_name)  # pylint: disable=protected-access
+                    # Legacy Elasticsearch engine
+                    if hasattr(searcher, '_es'):  # pylint: disable=protected-access
+                        index_exists = searcher._es.indices.exists(index=index_name)  # pylint: disable=protected-access
 
-                    index_mapping = searcher._es.indices.get_mapping(  # pylint: disable=protected-access
-                        index=index_name,
-                    ) if index_exists else {}
+                        index_mapping = searcher._es.indices.get_mapping(  # pylint: disable=protected-access
+                            index=index_name,
+                        ) if index_exists else {}
 
-                    if index_exists and index_mapping:
-                        return
+                        if index_exists and index_mapping:
+                            return
 
             # if reindexing is done during devstack setup step, don't prompt the user
             if setup_option or query_yes_no(self.CONFIRMATION_PROMPT, default="no"):

cms/djangoapps/contentstore/tests/test_courseware_index.py

@@ -504,6 +504,11 @@ def test_delete_course_from_search_index_after_course_deletion(self):
         """ Test for removing course from CourseAboutSearchIndexer """
         self._test_delete_course_from_search_index_after_course_deletion(self.store)
 
+    def test_empty_course(self):
+        empty_course = CourseFactory.create(modulestore=self.store, start=datetime(2015, 3, 1, tzinfo=UTC))
+        added_to_index = CoursewareSearchIndexer.do_course_reindex(self.store, empty_course.id)
+        assert added_to_index == 0
+
 
 @patch('django.conf.settings.SEARCH_ENGINE', 'search.tests.utils.ForceRefreshElasticSearchEngine')
 @ddt.ddt