Move the query to a scope, Lambda for reload data

app/models/app_usage.rb

@@ -1,4 +1,12 @@
 class AppUsage < ActiveRecord::Base
   validates :package_name, :usage_duration_in_seconds, :used_on, presence: true
   belongs_to :device
+
+  scope :app_usages_per_device_app_day, lambda {
+          AppUsage.select(:package_name,:device_id,:used_on).
+          order("used_on desc").
+          order("device_id").
+          order("package_name").
+          group("device_id","package_name","used_on").
+          sum("usage_duration_in_seconds")}
 end