如何在 Rails 中实现计数器缓存？

Question

我有一个帖子控制器和一个评论控制器。 帖子有很多评论，评论属于帖子。 关联是在打开 counter_cache 选项的情况下设置的：

#Inside post.rb
has_many :comments

#Inside comment.rb
belongs_to :post, :counter_cache => true

我的 posts 表中有一个 comments_count 列，该列默认为零，如下所示

add_column :posts, :comments_count, :integer, :default => 0

：我的评论控制器的 >create 操作，我有以下代码：

def create
  @posts = Post.find(params[:post_id])
  @comment = @post.comments.build(params[:comment])
  if @comment.save
    redirect_to root
  else
    render :action => 'new'
  end
end

我的问题：当调用 @comment.save 时，我收到以下错误：

ArgumentError in CommentsController#create

wrong number of arguments (2 for 0)

正在删除 :counter_cache => ; comment.rb 中的 true 完全解决了问题，因此我假设这是导致此模糊错误的原因。我在这里缺少什么？ 我怎样才能保存我的评论，同时仍然让 Rails 处理我的帖子的 counter_cache ？

谢谢！

---

更新 - 附加应用程序跟踪：

/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:987:in `update_all'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:987:in `update_counters_without_lock'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/locking/optimistic.rb:176:in `update_counters'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:1006:in `increment_counter'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/associations.rb:1367:in `belongs_to_counter_cache_after_create_for_feed_entry'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:178:in `send'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:178:in `evaluate_method'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:166:in `call'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:93:in `run'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:92:in `each'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:92:in `send'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:92:in `run'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/callbacks.rb:276:in `run_callbacks'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/callbacks.rb:344:in `callback'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/callbacks.rb:267:in `create'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:2915:in `create_or_update_without_callbacks'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/callbacks.rb:250:in `create_or_update'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/base.rb:2573:in `save_without_validation'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/validations.rb:1090:in `save_without_dirty'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/dirty.rb:79:in `save_without_transactions'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:229:in `send'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:229:in `with_transaction_returning_status'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/connection_adapters/abstract/database_statements.rb:136:in `transaction'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:182:in `transaction'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:228:in `with_transaction_returning_status'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:196:in `save'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:208:in `rollback_active_record_state!'
/Library/Ruby/Gems/1.8/gems/activerecord-2.3.8/lib/active_record/transactions.rb:196:in `save'
/Users/yuval/Sites/rails/blog/app/controllers/comments_controller.rb:6:in `create'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:1331:in `send'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:1331:in `perform_action_without_filters'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/filters.rb:617:in `call_filters'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/filters.rb:610:in `perform_action_without_benchmark'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/core_ext/benchmark.rb:17:in `ms'
/Library/Ruby/Gems/1.8/gems/activesupport-2.3.8/lib/active_support/core_ext/benchmark.rb:17:in `ms'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/benchmarking.rb:68:in `perform_action_without_rescue'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/rescue.rb:160:in `perform_action_without_flash'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/flash.rb:151:in `perform_action'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:532:in `send'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:532:in `process_without_filters'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/filters.rb:606:in `process'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:391:in `process'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/base.rb:386:in `call'
/Library/Ruby/Gems/1.8/gems/actionpack-2.3.8/lib/action_controller/routing/route_set.rb:438:in `call'

请注意，唯一不必直接与 Rails 框架相关的行是：

/Users/yuval/Sites/rails/blog/app/controllers/comments_controller.rb:6:in `create'

第 6 行如下：

if @comment.save

---

编辑 2： @posts/@post 是我在为 StackOverflow 编写简化示例时的拼写错误，我的实际应用程序没有错误。

检查@comment，它似乎完全有效 - 它返回的正是我所期望的 - 一个新的注释实例，其中包含我通过 build 传递给它的任何信息。仅当对其调用 save 方法时，它才会爆炸。

感谢您迄今为止提出的所有建议。还有其他想法吗？

Answer 1

我用你的代码运行了一个示例 Rails 应用程序，它对我来说一切正常。

我建议像 hurikhan77 所建议的那样进行更多调试，看看这是否只是 dain 建议的 @posts / @post 问题。

另外，尝试在控制台中使用一些非常简单的内容创建帖子和评论，看看它是否有效。

$ ruby script/console

# add whatever fields are necessary to create     
> @p = Post.create(:title => "TestPost1")
  # => #<Post id: 3, ...

# again, add whatever is necessary to create
> @c = @p.comments.create(:comment => "TestComment1")
  # => #<Comment id: 8, ...

> Post.find(:last).comments_count
  # => 1

看看这会给你带来什么。

/ 太平绅士

Answer 2

这可能完全不合时宜，但你使用@posts 然后@post？

Answer 3

参数错误
CommentsController#create

参数数量错误（2 代表 0）

您收到此错误是因为 @comment 不是您期望的对象。尝试通过插入来调试它：

logger.debug @comment.inspect

你会看到一些意想不到的东西，它至少应该引起人们的注意。这应该是您将 Post.find(...) 分配给 @posts 但后来尝试使用 @post 的 Clou。