问Rails4，加载ActiveRecord模型不工作

EN

我的routes.rb文件是

 namespace(:api){
  resources :open_conversations do
    resources :open_answers, :only => [:index, :create, :destroy]
 end

}

以及OpenConversation和OpenAnswer控制器文件

class OpenConversation < ActiveRecord::Base
  has_many :open_answers, :dependent => :destroy
end


class OpenAnswer < ActiveRecord::Base
  belongs_to :open_conversation
end

并将OpenConversation模型加载到OpenAnswer控制器中。

class Api::OpenAnswersController < Api::ApplicationController

  before_filter :get_conversation

  def get_conversation
    binding.pry
    @con = OpenConversation.find(params[:open_conversation_id])
    @answers = @con.open_answers
  end
end

==============这是IRB调试日志

6 pry(#)> OpenConversation

=> Api::OpenConversation

7 pry(#)> OpenConversation.find(params:open_conversation_id)

非初始化常数Api::OpenAnswersController::OpenConversation：NameError

出发地(撬)：6:in `get_conversation‘

8 pry(#)> OpenConversation

非初始化常数Api::OpenAnswersController::OpenConversation：NameError

出发地(撬)：7:in `get_conversation‘

9 pry(#)> OpenConversation.class

NameError:未初始化常量Api::OpenAnswersController::OpenConversation

出发地(撬)：8:in `get_conversation‘

为什么OpenConversation模型加载喜欢模块？