调整

app/models/memo.rb

@@ -15,6 +15,7 @@ class Memo < ApplicationRecord
   has_many :descendants, foreign_key: :root_id, class_name: 'Memo'
   has_many :children, foreign_key: :parent_id, class_name: 'Memo'
   has_many :attachments, as: :container, dependent: :destroy
+  has_many :tidings, as: :container, dependent: :destroy
 
   scope :field_for_list, lambda{
     select([:id, :subject, :author_id, :sticky, :updated_at, :language, :reward, :all_replies_count, :viewed_count, :forum_id])