删除作品时，删除作品的点赞数

app/models/student_work.rb

@@ -9,5 +9,11 @@ class StudentWork < ActiveRecord::Base
   belongs_to :project
   has_one :student_work_test
 
+  before_destroy :delete_praise
+
   acts_as_attachable
+
+  def delete_praise
+    PraiseTread.where("praise_tread_object_id = #{self.id} AND praise_tread_object_type = 'StudentWork'").destroy_all
+  end
 end