3

它有时会发生在我的产品环境中（大多数时候都可以）。我怀疑它是否与 sessionmaker func 中的参数'expire_on_commit'有关

@close_session
def func():
    session = DBSession() # scoped_session, thread_local
    m = Model()
    m.content = 'content'
    session.add(m)
    try:
        session.commit()
    except SQLAlchemyError as e:
        session.rollback()
        raise_my_exception()
    return m.id

close_session 是一个装饰器，它将在“finally”部分执行“DBSession().close()”。ObjectDeleteError 发生在“return m.id”行

SQLAlchemy 配置：

engines = {                                                                        
    'master': create_engine(                                                       
        settings.MASTER_URL, echo=settings.ECHO_SQL, pool_recycle=3600),           
    'slave': create_engine(                                                        
        settings.SLAVE_URL, echo=settings.ECHO_SQL, pool_recycle=3600),            
}                                                                                  


class RoutingSession(Session):                                                     
    def get_bind(self, mapper=None, clause=None):                                  
        #return engines['master']                                                  
        if self._flushing:                                                         
            return engines['master']                                               
        else:                                                                      
            return engines['slave']                                                

DBSession = scoped_session(sessionmaker(class_=RoutingSession))

ObjectDeletedError 文档：

class ObjectDeletedError(sqlalchemy.exc.InvalidRequestError)
 |  A refresh operation failed to retrieve the database
 |  row corresponding to an object's known primary key identity.
 | 
 |  A refresh operation proceeds when an expired attribute is
 |  accessed on an object, or when :meth:`.Query.get` is
 |  used to retrieve an object which is, upon retrieval, detected
 |  as expired.   A SELECT is emitted for the target row
 |  based on primary key; if no row is returned, this
 |  exception is raised.
 | 
 |  The true meaning of this exception is simply that
 |  no row exists for the primary key identifier associated
 |  with a persistent object.   The row may have been
 |  deleted, or in some cases the primary key updated
 |  to a new value, outside of the ORM's management of the target
 |  object.
 |

编辑：我在“session.commit()”之后放置了“return m.id”，仍然引发了 ObjectDeletedEror

@close_session
def func():
    session = DBSession() # scoped_session, thread_local
    m = Model()
    m.content = 'content'
    session.add(m)
    try:
        session.commit()
        return m.id
    except SQLAlchemyError as e:
        session.rollback()
        raise_my_exception()

编辑2：

我更改了我的 RoutingSession 以仅返回 master 并且错误消失了：

class RoutingSession(Session):                                                     
    def get_bind(self, mapper=None, clause=None):                                  
        return engines['master']

所以它必须与这个主/从配置有关。

关于如何解决它的任何想法？

4

2 回答 2

9

DBSession 是使用默认值创建的 (expire_on_commit = True)。所以提交后，当返回obj.id时，obj已经过期。所以session会从slave数据库（engines['slave']）获取obj，但是由于主从延迟，对应的记录还没有同步到slave。

于 2014-12-20T03:51:42.447 回答
2

此错误意味着以下两种情况之一：

  1. raise_my_exception() 实际上并没有引发异常，因此在 rollback() 期间代码落入“return m.id”并且该行不存在，因为它已回滚。

  2. 在您说 session.commit() 和“return m.id”之间，一个并发线程或进程正在删除该行。提交后数据从“m”过期，以便下一次访问将从数据库中检索此对象的最新数据，并将其放入新事务中。这与您“有时（大多数时候没问题）”的描述一致。- 偶尔发生的问题通常是由于并发问题。

于 2012-11-06T22:14:17.110 回答