model validates_length_of :content, :maximum => 400, :message => "店铺描述小于 200 字"
view form_for @seo, :url => "#{url}",:method => "post" do |f| error_messages_for :name
http://guides.rubyonrails.org/active_record_validations.html#displaying-validation-errors-in-views
return 的值就是返给页面显示的值
