On Apr 20, 2011, at 4:37 AM, can xiang wrote:
> Hi,
>
> I have a problem of bulk deleting from a sharded session, I tried to
> search the previous posts without any finding.
>
> I have the following table:
>
> usersession_table = Table('kg_usersession', meta,
> Column('session_id', String(32),
> primary_key=True),
> Column('user_id', BigInteger, index=True,
> nullable=False),
> Column('create_time', DateTime, index=True),
> Column('expire_time', DateTime, index=True),
> Column('site', String(10)),
> mysql_engine='MyISAM'
> )
>
> I use horizontal sharding by "session_id", with the following shard
> chooser:
>
> def shard_chooser(mapper, instance, clause=None):
> if instance:
> return shard_value(instance.session_id)
>
> Then, I want to delete all record earlier than a given expire_time,
> with the following code:
>
> session.query(UserSession).filter(UserSession.expire_time<=expire_time).delete();
range deletions are not supported by the ShardedSession extension right now.
You'd need to implement your own delete() onto ShardedQuery.
Note that the horizontal shard extension really should have been an example,
not a full extension. It's really just a proof of concept and real-world
horizontal sharding scenarios will usually need to tweak it for specific use
cases.
>
> It raises an error:
>
> Traceback (most recent call last):
> File "delete_expire_session.py", line 20, in <module>
> delete_expire_session(expire_time)
> File "delete_expire_session.py", line 13, in delete_expire_session
>
> session.query(UserSession).filter(UserSession.expire_time<=expire_time).delete();
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/orm/query.py", line 2142, in delete
> result = session.execute(delete_stmt, params=self._params)
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/orm/session.py", line 726, in execute
> engine = self.get_bind(mapper, clause=clause, **kw)
> File "/usr/local/lib/python2.6/dist-packages/SQLAlchemy-0.6.5-
> py2.6.egg/sqlalchemy/ext/horizontal_shard.py", line 73, in get_bind
> return self.__binds[shard_id]
> KeyError: None
>
> I guess shard_chooser return None because of "instance" is None at
> runtime. I read from the docs: shard_chooser maybe in "some round-
> robin scheme". But I don't have any idea what does it exactly mean in
> my case.
>
> I appreciate any advice.
>
> Best regards!
> can
>
>
> PS: you can access partial source code in the gist:
> https://gist.github.com/930708
>
> --
> You received this message because you are subscribed to the Google Groups
> "sqlalchemy" group.
> To post to this group, send email to sqlalchemy@googlegroups.com.
> To unsubscribe from this group, send email to
> sqlalchemy+unsubscr...@googlegroups.com.
> For more options, visit this group at
> http://groups.google.com/group/sqlalchemy?hl=en.
>
--
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to sqlalchemy@googlegroups.com.
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en.
