Overrode search backend's search method

The previous attempt to resolve this issue did not work. Now we are
explicitly removing the code that made unnecessary Elasticsearch calls.

LEARNER-2188

course_discovery/apps/edx_haystack_extensions/backends.py

+import logging
+
+import elasticsearch
+from haystack.backends import log_query
 from haystack.backends.elasticsearch_backend import ElasticsearchSearchBackend, ElasticsearchSearchEngine
+from haystack.models import SearchResult
 
 from course_discovery.apps.edx_haystack_extensions.elasticsearch_boost_config import get_elasticsearch_boost_config
 
+logger = logging.getLogger(__name__)
+
 
 class SimpleQuerySearchBackendMixin(object):
     """
@@ -121,12 +128,54 @@ class ConfigurableElasticBackend(ElasticsearchSearchBackend):
 # pylint: disable=abstract-method
 class EdxElasticsearchSearchBackend(SimpleQuerySearchBackendMixin, NonClearingSearchBackendMixin,
                                     ConfigurableElasticBackend):
+    @log_query
     def search(self, query_string, **kwargs):
+        if len(query_string) == 0:
+            return {
+                'results': [],
+                'hits': 0,
+            }
+
         # NOTE (CCB): Haystack by default attempts to read/update the index mapping. Given that our mapping doesn't
         # frequently change, this is a waste of three API calls. Stop it! We set our mapping when we create the index.
         self.setup_complete = True
-
-        return super().search(query_string, **kwargs)
+        # if not self.setup_complete:
+        #     self.setup()
+        logger.info('DEBUG: Skipped Haystack setup call')
+
+        search_kwargs = self.build_search_kwargs(query_string, **kwargs)
+        search_kwargs['from'] = kwargs.get('start_offset', 0)
+
+        order_fields = set()
+        for order in search_kwargs.get('sort', []):
+            for key in order.keys():
+                order_fields.add(key)
+
+        geo_sort = '_geo_distance' in order_fields
+
+        end_offset = kwargs.get('end_offset')
+        start_offset = kwargs.get('start_offset', 0)
+        if end_offset is not None and end_offset > start_offset:
+            search_kwargs['size'] = end_offset - start_offset
+
+        try:
+            # pylint: disable=unexpected-keyword-arg
+            raw_results = self.conn.search(body=search_kwargs,
+                                           index=self.index_name,
+                                           doc_type='modelresult',
+                                           _source=True)
+        except elasticsearch.TransportError as e:
+            if not self.silently_fail:
+                raise
+
+            self.log.error("Failed to query Elasticsearch using '%s': %s", query_string, e, exc_info=True)
+            raw_results = {}
+
+        return self._process_results(raw_results,
+                                     highlight=kwargs.get('highlight'),
+                                     result_class=kwargs.get('result_class', SearchResult),
+                                     distance_point=kwargs.get('distance_point'),
+                                     geo_sort=geo_sort)
 
 
 class EdxElasticsearchSearchEngine(ElasticsearchSearchEngine):