多线程scoped_session中的SQLAlchemy

Posted 2021-04-25

我试图在多线程环境中使用SQLAlchemy，但我得到奇怪的错误。情况如下：

线程1启动所有SQLAlchemy对象（Engine，Models，scoped_session等）

然后，线程2尝试使用scoped_session对象在数据库上进行查询。不幸的是，从线程2错误被抛出。

我创建了一个简单的测试用例来说明我想要实现的目标：

import sqlalchemy
from sqlalchemy import Column, Integer, String, Boolean, desc, asc, func

from sqlalchemy import create_engine
sqlEngine = create_engine('sqlite:///:memory:',echo=False)
from sqlalchemy.orm import sessionmaker, scoped_session
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

class SimpleTable(Base):
    __tablename__ = 'SimpleTable'

    orderID = Column(Integer, primary_key=True)
    field = Column(Integer)

    def __repr__(self):
    return "<Simple Table: %s>" % self.field

session_factory = sessionmaker(bind=sqlEngine)
Session = scoped_session(session_factory)
Base.metadata.create_all(sqlEngine)

for i in xrange(10):
    var = SimpleTable(field=10)
    Session.add(var)

Session.query(SimpleTable).all()
Session.commit()

from threading import Thread

class TestThread(Thread):

    def run(self):
    print "Running test thread..."
    try:
        print 'Grabbing data from thread:'+str(Session.query(SimpleTable).all())
    except BaseException as e:
        print e
    print "Done running test thread..."

TestThread().start()

print 'Grabbing data outside thread:'+str(Session.query(SimpleTable).all())

这是带有错误消息的输出：

Running test thread...
(OperationalError) no such table: SimpleTable u'SELECT "SimpleTable"."orderID" AS "SimpleTable_orderID", "SimpleTable".field AS "SimpleTable_field" 
FROM "SimpleTable"' ()
Done running test thread...
Grabbing data outside thread:[<Simple Table: 10>, <Simple Table: 10>, <Simple Table: 10>, <Simple Table: 10>, <Simple Table: 10>, <Simple Table: 10>, <Simple Table: 10>, <Simple Table: 10>, <Simple Table: 10>, <Simple Table: 10>]

该表因某种原因不存在。我已经阅读并重读了文档以及互联网上的多个帖子，并且似乎scoped_session存在于上述的确切情况。有人可以开导我吗？

答案

我遇到了同样的情况。我怀疑“在内存中”db不支持scoped_session。当我切换到基于普通文件的数据库时，问题就消失了。