Ruby on rails 如何在RubyonRails中使用dependent？

用户\u controller.rb：

class User < ActiveRecord::Base
  has_many :posts, dependent: :restrict_with_exception
end

---

为什么它没有捕获异常？

因为没有关联的post记录什么？？？？？？？？？？？？？？？？？？？？？

class UsersController < ApplicationController
...
  def destroy
    @user.destroy   
    flash[:danger] = "Success"
    redirect_to users_path
  rescue => e
    flash[:danger] = "Error"
    redirect_to @user
  end
...
end