Django模型在查詢中讀取和創建？

Question

我想根據模型的最後一個id在Django模型中插入一行。我的查詢是喜歡，

Order.objects.create(group=123131, identifier=friendly_invoice.encode(Order.objects.last().id)) 
# group and identifier are unique together 

我登錄查詢如圖http://www.dabapps.com/blog/logging-sql-queries-django-13/，

(0.016) SELECT `order`.`id`, `order`.`group`, `order`.`identifier`, `order`.`created`, `order`.`modified` FROM `order` ORDER BY `order`.`id` DESC LIMIT 1; args=() 
DEBUG 2015-12-30 12:16:21,881 (0.016) SELECT `order`.`id`, `order`.`group`, `order`.`identifier`, `order`.`created`, `order`.`modified` FROM `order` ORDER BY `order`.`id` DESC LIMIT 1; args=() 
DEBUG 2015-12-30 12:16:21,881 (0.016) SELECT `order`.`id`, `order`.`group`, `order`.`identifier`, `order`.`created`, `order`.`modified` FROM `order` ORDER BY `order`.`id` DESC LIMIT 1; args=() 
(0.000) INSERT INTO `order` (`group`, `identifier`, `created`, `modified`) VALUES ('123131', '378ETGY', '2015-12-30 06:46:21', '2015-12-30 06:46:21'); args=[u'123131', '378ETGY', u'2015-12-30 06:46:21', u'2015-12-30 06:46:21'] 
DEBUG 2015-12-30 12:16:21,881 (0.000) INSERT INTO `order` (`group`, `identifier`, `created`, `modified`) VALUES ('123131', '378ETGY', '2015-12-30 06:46:21', '2015-12-30 06:46:21'); args=[u'123131', '378ETGY', u'2015-12-30 06:46:21', u'2015-12-30 06:46:21'] 
DEBUG 2015-12-30 12:16:21,881 (0.000) INSERT INTO `order` (`group`, `identifier`, `created`, `modified`) VALUES ('123131', '378ETGY', '2015-12-30 06:46:21', '2015-12-30 06:46:21'); args=[u'123131', '378ETGY', u'2015-12-30 06:46:21', u'2015-12-30 06:46:21'] 

這是創建以dB兩個SQL查詢。我相信如果這個代碼是由兩個並行請求執行的話，這將會出錯。

如何以安全的方式編寫此查詢？

Answer 1

我用https://docs.djangoproject.com/en/1.7/topics/db/transactions/#savepoints

from django.db import transaction 

# open a transaction 
@transaction.atomic 
def viewfunc(request): 
    ...