Merge branch 'feature/batch_delete_notification_statistic_data' into 'master'

Feature/batch delete notification statistic data

See merge request !7

lib/tasks/data_migrations/version_v1.rake

+namespace :data_migrations do
+  namespace :version do
+  
+    desc "batch delete notification_statistics data"
+    task :v1_batch_delete_notification_statistics_data => :environment do
+      first_id = NotificationStatistic.first.id
+      last_object = NotificationStatistic.where("notification_statistics.created_at < ?", '2020-05-30 16:00:00').last
+      
+      
+      first_id.step(last_object.id, 10000) do |i|
+        NotificationStatistic.where(id: [i...i+10000]).delete_all
+      end if last_object.present?
+    end
+  end
+end
\ No newline at end of file