尝试rforum的时候解决思路

尝试rforum的时候
rake db:migrate的时候 002_add_post_counter.rb 报错


class AddPostCounter < ActiveRecord::Migration
  def self.up
  add_column :topics, :post_counter, :integer, :default => 1
  Topic.find(:all).each do |topic|
  topic.update_post_counter
  topic.save
  end
  end

  def self.down
  remove_column :topics, :post_counter
  end
end

错误如下
-- add_column(:topics, :post_counter, :integer, {:default=>1})
  -> 0.0340s
rake aborted!
An error has occurred, this and all later migrations canceled:

uninitialized constant AddPostCounter::Topic

(See full trace by running task with --trace)

这个是什么问题啊 死活找不到答案 求助各位达达
另求装过rforum的达达留个QQ 装这个好难啊

[解决办法]
rforum 是个开源项目嘛？还没听过哦，去看看！