This is my "serials" table and mapper:
table.serials = Table("serials", instance.metadata.default,
Column("prefix", String(32), primary_key=True),
Column("month", String(32), nullable=False),
Column("count", Integer, nullable=False),
)
class Serial(object):
pass
mapperSerial = mapper(Serial, table.serials)
I need a getSerial(prefix) to get a unique serial number depend on current
month, here's my code using orm:
def getSerial(prefix):
from datetime import datetime
today = datetime.today()
month = "%s%02d" % (str(today.year)[2:], today.month)
count = None
query = instance.session.default.query(Serial)
serial = query.get(prefix)
if serial is None:
serial = Serial()
serial.prefix = prefix
serial.month = month
serial.count = 1
instance.session.default.save(serial)
if serial.month != month:
serial.month = month
serial.count = 1
count = serial.count
serial.count += 1
instance.session.default.flush()
instance.session.default.expunge(serial)
return "%s-%s%04d" % (prefix, month, count)
But if there're two or more clients run getSerial() at the same time,
they'll get same result and will cause some problem. So I write codes use
"LOCK TABLES" in my first post in this thread. Can the orm do the same thing
beautifully? For "group version" of my program, it use MySQL; and "single
machine version", it use SQLite.
2007/6/22, Michael Bayer <[EMAIL PROTECTED]>:
>
>
> conn = engine.connect()
> trans = conn.begin()
> ...etc
> trans.commit()
>
> table locking is usually either implicit to SQL operations performed
> within the transaction or using a construct like SELECT..FOR UPDATE,
> but you can still issue your straight text if you like (but LOCK
> TABLES isnt portable).
>
>
> On Jun 21, 5:41 pm, "Can Xue" <[EMAIL PROTECTED]> wrote:
> > I'm using MySQL and when I need to lock a table, I do:
> >
> > conn = engine.connect()
> > conn._autocommit = dummyFunc
> > conn.execute("LOCK TABLES tablename WRITE")
> > try:
> > ...
> > conn.execute("COMMIT")
> > except:
> > conn.execute("ROLLBACK")
> > ...
> > finally:
> > conn.execute("UNLOCK TABLES")
> > conn.close()
> >
> > Are there any more pythonic ways to do such tasks?
> >
> > --
> >
> > XUE Can
>
>
> >
>
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