Rails: Reraise Mongoid and BSON exceptions to my own exception

I have my own exception handler:

module Frog
  module Errors
    class NotFound < FrogError
      attr_accessor :exception

      def initialize (exception)
        self.exception = exception
      end

      def as_json
        {
          :error => {
            :message => "Object not found"
          }
        }
      end 

      def status_code
        404
      end
    end
  end
end

In application_controller.rb this exception is handled by

rescue_from Frog::Errors::FrogError, :with => :render_frog_error开发者_JS百科

and

def render_frog_error(exception)
   access_control_headers!
   render :json => exception, :status => exception.status_code
end

In my project i have BSON::InvalidObjectId and Mongoid::Errors::DocumentNotFound exceptions. I want to generate this exceptions by myself. I try this way:

rescue_from BSON::InvalidObjectId do 
   |ex| raise Frog::Errors::NotFound.new(ex) 
end

but it's not working. How can I reraise BSON adn Mongoid exception to mine?

---

I found this solution:

rescue_from BSON::InvalidObjectId, :with => :proxy_exception
rescue_from Mongoid::Errors::DocumentNotFound, :with => :proxy_exception

def proxy_exception(exception)
        exception = Frog::Errors::NotFound.new(exception)
        render_frog_error(exception) 
end