ruby-on-rails – Rails Active Record取消(保存或创建)before_c

system_details.rb(Model)

class SystemDetail < ActiveRecord::Base
  belongs_to :user
  attr_accessible :user_agent

  before_create :prevent_if_same    

  def agent
    Browser.new(ua: user_agent,accept_language: 'en-us')
  end

  def prevent_if_same
    rec = user.system_details.order('updated_at desc').first
    return true unless rec
    if rec.user_agent == user_agent
      rec.touch
      return false
    end
  end
end

prevent_if_same方法工作正常并且按预期工作但是当它返回false时引发异常ActiveRecord :: RecordNotSaved,并且该异常打破了rspec测试.我想要的是,它应该默默地取消保存而不引发异常.

system_detail_spec.rb(rspec)

require 'rails_helper'

RSpec.describe SystemDetail,:type => :model do      

  context '#agent' do
    it 'Checks browser instance' do
      expect(SystemDetail.new.agent).to be_an_instance_of(Browser)
    end
  end

  context '#callback' do    
    it 'Ensure not creating consecutive duplicate records' do
      user = create :end_user
      system_detail = create :system_detail,:similar_agent,user_id: user.id
      updated_at  = system_detail.updated_at
      system_detail2 = create :system_detail,user_id: user.id
      system_detail.reload

      expect(system_detail2.id).to be_nil
      expect(system_detail.updated_at).to be > updated_at
    end
  end        
end

第二次测试#callback由于异常而失败.

Failures:

1) SystemDetail#callback ensure not creating duplicate records
Failure/Error: system_detail2 = create :system_detail,user_id: user.id
ActiveRecord::RecordNotSaved:
ActiveRecord::RecordNotSaved

有没有办法在不引发异常的情况下默默取消保存？