ruby-on-rails – 如果我尝试进行计数器缓存,为什么会出现此错误？

我正在使用Rails 3.2.6.当我尝试进行计数器缓存时,我会以某种方式得到此错误.
我怎样才能解决这个问题？我在这个应用程序上做了同样的事情,但没有在这个模型上.
我的代码或关联有什么问题？

命令包exec rake db：migrate

日志

==  AddCommunityTopicsCountToCommunity: migrating =============================
-- add_column(:communities,:community_topics_count,:integer,{:default=>0})
   -> 0.0635s
rake aborted!
An error has occurred,all later migrations canceled:

community_topics_count is marked as readonly

车型/ community.rb

...
has_many :community_topics
...

车型/ community_topic.rb

...
belongs_to :community,counter_cache: true
...

迁移文件

class AddCommunityTopicsCountToCommunity < ActiveRecord::Migration
  def up
    add_column :communities,:default => 0

    Community.reset_column_information
    Community.all.each do |p|
      p.update_attribute :community_topics_count,p.community_topics.length
    end
  end

  def down
    remove_column :communities,:community_topics_count
  end
end

解决方法

class AddCommunityTopicsCountToCommunity < ActiveRecord::Migration
  def up
    add_column :communities,:default => 0

    Community.reset_column_information
    Community.all.each do |c|
      Community.reset_counters(c.id,:community_topics)
    end
  end
end