我使用的是Django 1.5.1并升级到Django 1.6.6。
在Django 1.5.1中,我使用select for update来保证原子执行。
job_qs = Job.objects.select_for_update().filter(pk=job.id)
for job in job_qs:
不幸的是,这会引发错误:
File "/srv/venvs/django-picdoc/local/lib/python2.7/site-packages/django/db/models/query.py", line 96, in __iter__
self._fetch_all()
File "/srv/venvs/django-picdoc/local/lib/python2.7/site-packages/django/db/models/query.py", line 857, in _fetch_all
self._result_cache = list(self.iterator())
File "/srv/venvs/django-picdoc/local/lib/python2.7/site-packages/django/db/models/query.py", line 220, in iterator
for row in compiler.results_iter():
File "/srv/venvs/django-picdoc/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 713, in results_iter
for rows in self.execute_sql(MULTI):
File "/srv/venvs/django-picdoc/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 776, in execute_sql
sql, params = self.as_sql()
File "/srv/venvs/django-picdoc/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 147, in as_sql
raise TransactionManagementError("select_for_update cannot be used outside of a transaction.")
TransactionManagementError: select_for_update cannot be used outside of a transaction.
解决这个问题有哪些解决方案?
答案 0 :(得分:22)
答案在错误中,将查询包装在事务中
Django的文档位于:https://docs.djangoproject.com/en/dev/topics/db/transactions/#django.db.transaction.atomic
一种方法是:
from django.db import transaction
def some_method():
with transaction.atomic():
job_qs = Job.objects.select_for_update().filter(pk=job.id)
for job in job_qs:
答案 1 :(得分:4)
从Django 2.0开始,默认情况下锁定相关的行(不确定之前的行为是什么),并且可以使用select_related
参数以与of
相同的样式指定要锁定的行:
"默认情况下,select_for_update()会锁定查询选中的所有行。例如,除了查询集模型的行之外,select_related()中指定的相关对象的行也会被锁定。如果不需要,请使用与select_related()相同的字段语法,在select_for_update(of =(...))中指定要锁定的相关对象。使用值' self'引用查询集的模型。"
https://docs.djangoproject.com/en/dev/ref/models/querysets/#select-for-update
答案 2 :(得分:0)
对我来说,即使使用with transaction.atomic():
,它也发生了。问题是我们没有在'ATOMIC_REQUESTS': True
文件中设置settings.py
。现在这解决了问题。
如此处所述:https://docs.djangoproject.com/en/3.1/topics/db/transactions/
“在要为其启用此行为的每个数据库的配置中将ATOMIC_REQUESTS
设置为True
。”
因此,在settings.py
中,我们添加了:
DATABASES = {
'default': {
'ENGINE': 'django.db.backends.mysql',
'NAME': os.environ['DB_NAME'],
'USER': os.environ['DB_USER'],
'PASSWORD': os.environ['DB_PASSWORD'],
'HOST': os.environ['DB_HOST'],
'PORT': '3306',
'ATOMIC_REQUESTS': True
}
}