我有一个连接到 MySQL 数据库的 celery 项目。其中一个表是这样定义的:

class MyQueues(Base):
    __tablename__ = 'accepted_queues'

    id = sa.Column(sa.Integer, primary_key=True)
    customer = sa.Column(sa.String(length=50), nullable=False)
    accepted = sa.Column(sa.Boolean, default=True, nullable=False)
    denied = sa.Column(sa.Boolean, default=True, nullable=False)

此外，在我的设置中

THREADS = 4

我被困在 code.py 中的一个函数中:

def load_accepted_queues(session, mode=None):

    #make query  
    pool = session.query(MyQueues.customer, MyQueues.accepted, MyQueues.denied)

    #filter conditions    
    if (mode == 'XXX'):
        pool = pool.filter_by(accepted=1)
    elif (mode == 'YYY'):
        pool = pool.filter_by(denied=1)
    elif (mode is None):
        pool = pool.filter(\
            sa.or_(MyQueues.accepted == 1, MyQueues.denied == 1)
            )

   #generate a dictionary with data
   for i in pool: #<---------- line 90 in the error
        l.update({i.customer: {'customer': i.customer, 'accepted': i.accepted, 'denied': i.denied}})

运行时出现错误:

[20130626 115343] Traceback (most recent call last):
  File "/home/me/code/processing/helpers.py", line 129, in wrapper
    ret_value = func(session, *args, **kwargs)
  File "/home/me/code/processing/test.py", line 90, in load_accepted_queues
    for i in pool: #generate a dictionary with data
  File "/home/me/envs/me/local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2341, in instances
    fetch = cursor.fetchall()
  File "/home/me/envs/me/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 3205, in fetchall
    l = self.process_rows(self._fetchall_impl())
  File "/home/me/envs/me/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 3174, in _fetchall_impl
    self._non_result()
  File "/home/me/envs/me/local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 3179, in _non_result
    "This result object does not return rows. "
ResourceClosedError: This result object does not return rows. It has been closed automatically

所以主要是这部分

ResourceClosedError: This result object does not return rows. It has been closed automatically

有时还有这个错误:

DBAPIError: (Error) (, AssertionError('Result length not requested length:\nExpected=1. Actual=0. Position: 21. Data Length: 21',)) 'SELECT accepted_queues.customer AS accepted_queues_customer, accepted_queues.accepted AS accepted_queues_accepted, accepted_queues.denied AS accepted_queues_denied \nFROM accepted_queues \nWHERE accepted_queues.accepted = %s OR accepted_queues.denied = %s' (1, 1)

我无法正确重现错误，因为它通常在处理大量数据时发生。我尝试将 THREADS = 4 更改为 1 并且错误消失了。无论如何，这不是解决方案，因为我需要将线程数保持在 4 上。

此外，我对使用的必要性感到困惑

for i in pool: #<---------- line 90 in the error

或

for i in pool.all(): #<---------- line 90 in the error

找不到合适的解释。

总而言之:有什么建议可以跳过这些困难吗？

最佳答案

All together: any advise to skip these difficulties?

是的。您绝对不能在多个线程中同时使用 session (或与该 session 关联的任何对象)或连接，尤其是对于 DBAPI 连接非常线程不安全的 MySQL-Python * .您必须组织您的应用程序，以便每个线程处理它自己的专用 MySQL-Python 连接(因此 SQLAlchemy 连接/ session /与该 session 关联的对象)，而不会泄漏到任何其他线程。

• 编辑:或者，您可以使用互斥锁将对 session /连接/DBAPI 连接的访问​​限制为一次只能访问其中一个线程，尽管这种情况不太常见，因为所需的高度锁定往往会破坏首先使用多线程的目的。

关于python - Celery 和 SQLAlchemy - 此结果对象不返回行。已经自动关闭，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/17317344/