在ActiveRecord中按字段查找未正常工作

我有一个导航系统,可以为任何链接设置提供永久链接。

当我通过脚本/控制台运行该行时,它返回的结果是:

>> Navigation.find_by_permalink("gems")
=> #<Navigation id: 10, text: "Gems", parent: nil, destination_controller: "pages", destination_action: "show", destination_id: "1", permalink: "gems", created_at: "2009-12-26 14:56:28", updated_at: "2009-12-26 14:56:28", previous: 9>

当我进入我的应用程序时,我会得到:

ActiveRecord::RecordNotFound in NavigationsController#permalink

 Couldn't find Navigation without an ID

我的请求是“/permalink/gems”,相关路线是:

map.permalink "permalink/:permalink", :controller => 'navigations', :action => 'permalink'

处理该请求的控制器代码是:

def permalink
    @nav=Navigation.find_by_permalink(params[:permalink])
    redirect_to :controller => @nav.destination_controller, :action => @nav.destination_action, :id => @nav.destination_id
end

有人知道这是为什么吗?