diff --git a/temp_file/app/models/site.rb b/temp_file/app/models/site.rb
index 7bf7d57..c78e4ca 100644
--- a/temp_file/app/models/site.rb
+++ b/temp_file/app/models/site.rb
@@ -73,7 +73,7 @@ class Site
   mount_uploader :mobile_icon, ImageUploader
   Impression.class_eval{
     def self.group_by(field,day_limit,start_day=Date.today,format = 'day')
-      limit_ele = Impression.desc(:id).where({ created_at: { "$lt" => start_day-(day_limit-2).days }}).first
+      limit_ele = self.desc(:id).where({ created_at: { "$lt" => start_day-(day_limit-2).days }}).first
       key_op = [['year','$year'],['month', '$month'], ['day', '$dayOfMonth']]
       key_op = key_op.take(1 + key_op.find_index { |key, op| format == key })
       project_date_fields = Hash[*key_op.collect { |key, op| [key, {op => "$#{field}"}] }.flatten]