Called id for nil, which would mistakenly be 4 错误解决之一

Called id for nil, which would mistakenly be 4 -- if you really wanted the id of nil, use object_id
这种问题如果是在一个事务中，你使用Customer.new的话，然后你又对customer进行一系列的操作，如下示例：
然后当你在save的时候就会报以上的错误
customer = Customer.new(attr)
      customer.channel_type = "101"
      customer.channel_id = 101
      customer.sales_id = 101
customer.save! #此处会报错

此时的解决办法就是把new 改为 create然后就可以了

customer = Customer.create(attr)
      customer.channel_type = "101"
      customer.channel_id = 101
      customer.sales_id = 101
  customer.save!
  如此代码为正确

具体原因尚未了解，希望高人解答！