cache learning objects all_by_score

app/repositories/orient_db/learning_object_repository.rb

@@ -137,8 +137,16 @@ module OrientDb
     end
 
     def all_by_score_from_offset_to_limit(offset, limit)
-      objects_hash = connection.query "SELECT FROM LearningObject ORDER BY score DESC LIMIT #{limit} SKIP #{offset}", limit: limit
-      build_objects(objects_hash) || []
+      return [] if offset.blank? || limit.blank?
+
+      # expensive query
+      key = 'learning_objects/all/score/' + offset.to_s + '/' + limit.to_s
+      objects_hash = Rails.cache.fetch(key, expires_in: 6.hours) do
+        objects = connection.query "SELECT FROM LearningObject ORDER BY score DESC LIMIT #{limit} SKIP #{offset}", limit: limit
+        objects.map { |o| { 'rid' => o['@rid'] } }
+      end
+
+      LearningObjectBuilder.build(objects_hash)
     end
 
     def get_subjects(learning_object)