Hi,
After some more internal discussions we tried and realized that the version
col is not really required at the child table level.
The second commit in the sample code fails because the version value on the
parent row has already moved ahead.
Please confirm if the understanding/conclusion is correct.
Regards,
Naresh
On Mon, Nov 29, 2010 at 2:21 PM, Naresh nkhal...@vayana.in wrote:
Hi,
We have a parent class/table (Notification/notifications) and a child
class/table(BusinessNotification/business_notifications).
Both of them have a version_id_col defined.
We are facing ConcurrentModificationException errors for the model at
the end of the mail.
The problem is because the update state generated uses 'None' a the
value for notifications.version column.
We tried removing the version_id_col mapper arg in the child class -
BusinessNotification and then the error went away and the update
statement used the correct version column value to update.
So, firstly we are wondering how do we fix the situation that we can
have a version_id_col in the child class/table as well?
Upon further investigations, we noticed that in the other parts of
the application we used the following approach.
parent_table = Table( ... )
class Parent(DeclarativeBase):
__table__ = parent_table
__mapper_args__ = {'polymorphic_on': parent_table.c.type,
'version_id_col': parent_table.c.version}
child1_table = Table( ... )
class Child1(DeclarativeBase)
__table__ = child1_table
__mapper_args__ = {'polymorphic_identity':'c1',
'version_id_col':child1_table.c.version_num}
With the above style of coding our models, we don't get
ConcurrentModificationException, but any update statement to the
parent_table does not use version column.
Please throw some light on these behaviors.
Regards,
Naresh
P.S. The model and sample client code follows.
--
class Notification(DeclarativeBase):
This entity represents the notifications saved for sending
later
__tablename__ = 'notifications'
__table_args__ = {mysql_engine:InnoDB,
mysql_row_format:DYNAMIC,
mysql_charset:utf8}
id = Column(bigint, primary_key=True, autoincrement=False)
entid = Column(bigint, ForeignKey('enterprises.entid',
name='fk_notifn_entid'), nullable=False)
notification_type = Column(types.String(30), nullable=False)
source = Column(types.String(30), nullable=False)
data = Column(text_type, nullable=False)
status = Column(types.String(12), nullable=False, default='new')
created_on = Column(types.DATETIME, nullable=False,
default=func.current_timestamp())
last_updated = Column(types.DATETIME, nullable=True,
onupdate=func.current_timestamp())
version = Column(types.SMALLINT, nullable=False, default=0)
__mapper_args__ = {'polymorphic_on': notification_type,
'polymorphic_identity':'incident', 'version_id_col': version}
class BusinessNotification(Notification):
This entity represents the business notifications
__tablename__ = 'business_notifications'
__table_args__ = {mysql_engine:InnoDB,
mysql_row_format:DYNAMIC,
mysql_charset:utf8}
notification_id = Column(bigint, ForeignKey('notifications.id',
name='fk_bn_notificationid'), primary_key=True, autoincrement=False)
event_id = Column(bigint, ForeignKey('doc_events.id',
name='fk_bn_eventid'), nullable=True)
created_on = Column(types.DATETIME, nullable=False,
default=func.current_timestamp())
last_updated = Column(types.DATETIME, nullable=True,
onupdate=func.current_timestamp())
version_num = Column(types.SMALLINT, nullable=False, default=0)
__mapper_args__ = {'polymorphic_identity':'event',
'version_id_col': version_num}
#__mapper_args__ = {'polymorphic_identity':'event'}
if __name__ == '__main__':
try :
qry = meta.Session().query(BusinessNotification).filter(and_(
BusinessNotification.status=='new',
BusinessNotification.created_on now()))
qry = qry.order_by(BusinessNotification.created_on)
all_notifications = qry.all()
for notification in all_notifications :
# some business logic to trigger status update
notification.status='in_progress'
meta.Session().commit()
except Exception as ex :
log.error(Error Identifying Notification Recipients)
log.exception(ex)
meta.Session().rollback()
finally :
meta.Session.remove()
--
Naresh Khalasi | Vayana Services (http://www.vayana.in) | +91-9892294598
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from sqlalchemy import create_engine
