Rails事务不回滚

我有一个从xml文件客户加载的方法 . 在文件下载之前，所有不在xml文件中的客户都被置于有效性错误状态 . 然后开始加载和更新现有客户 . 我将整个方法包装在一个事务中 . 但是如果你试图让下载客户端故意错误（它没有通过验证）我没有回滚整个事务 . 提示我做错了什么？如何在事务轨道中工作？

Code:

if customers_upload
  EXCHANGE_LOGGER.info("Start customers exchange")
  Customer.transaction do
    begin
      customers = xml.elements.to_a("//customer")

      customers_external_keys = []
      customers.each do |customer| 
        customers_external_keys << customer.elements['external_key'].text
      end          
      customers_false = Customer.where("external_key NOT IN (?)", customers_external_keys)
      customers_false.each do |customer_false|
        if customer_false.validity
          customer_false.update_attributes(validity: false)              
        end
      end
      EXCHANGE_LOGGER.info("#{customers_false.count} update validity in false")

      customers.each do |customer| 
        customer_name = customer.elements['name'].text
        customer_external_key = customer.elements['external_key'].text
        customer_address = customer.elements['address'].text
        customer_debt = customer.elements['debt'].text
        customer_db = Customer.find_by_external_key(customer_external_key)
        if !customer_db
          new_customer = Customer.create(name: customer_name, external_key: customer_external_key, address: customer_address, debt: customer_debt)
          EXCHANGE_LOGGER.info("#Create new customer #{customer_name}")
        else 
          if !customer_db.validity
            customer_db.update_attributes(name: customer_name, address: customer_address, debt: customer_debt, validity: true)
            EXCHANGE_LOGGER.info("#Change validity true and update customer #{customer_name}")            
          else
            customer_db.update_attributes(name: customer_name, address: customer_address, debt: customer_debt)
            EXCHANGE_LOGGER.info("#Update customer #{customer_name}")
          end        
        end
      end

    rescue => e
      if e.present?
        EXCHANGE_LOGGER.error("Customers not exchanged, message: #{e}")
        raise ActiveRecord::Rollback, "Call tech support!"
      end          
    end        
  end  
end

以下是exchange.log中的内容：

2013-11-29 10:53:23 INFO Start customers exchange
2013-11-29 10:53:33 INFO 3981 update validity in false
2013-11-29 10:53:33 ERROR Customers not exchanged, message: undefined method `text 'for nil: NilClass

这是内容development.log：

客户存在（0.2ms）SELECT 1 AS一个来自客户WHERE（客户.External_key ='CB001820'和客户.Id！= 3979）LIMIT 1（0.1ms）UPDATE客户SET validity = 0，updated_at ='2013- 11 - 29 10:53:33'客户在哪里ID = 3979客户是否存在（在0.2ms）选择1为一个客户WHERE（客户 . External_key ='CB001826和顾客 . ID！= 3980）LIMIT 1（0.1毫秒）UPDATE客户SET有效性= 0，的updated_at =“2013- 11月29日10:53:33'客户在哪里ID = 3980客户是否存在（在0.2ms）选择1为一个客户WHERE（客户 . External_key ='CB001822和顾客 . ID！= 3981）LIMIT 1（0.1毫秒）UPDATE客户SET有效性= 0，的updated_at =“2013- 11月29日10:53:33'客户在哪里Id = 3981（2.2ms）SELECT COUNT（*）FROM customers WHERE（external_key NOT IN（'12312'））（0.1ms）ROLLBACK

像ROLLBACK最后出现，但所有客户仍然有效:(