[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
On Apr 29, 2008, at 5:55 PM, David Bonner wrote: Hi, I'm trying to write a mapper extension that notifies a daemon about changes made to the DB that it needs to care about. But it looks like after_update() is actually getting called before the UPDATE is sent to the db. Not knowing a better way to debug it, I just threw a pdb.set_trace() into my after_update method to pause the process making the change, then queried the db directly using sql. It looks like the change hasn't made it to the DB yet, even though pdb.set_trace() is being triggered. after_update() is called after all UPDATE statements have been issued for that particular mapper. This includes *only* the table that is mapped by that mapper, not any other mappers. Is it possible that you are seeing an UPDATE being issued for an item that is related to your parent via a many-to-one ? Or that you have multiple ME's with after_update() at play and perhaps you're seeing a different one fire off. --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
then queried the db *directly using sql*. It looks like the change hasn't made it to the DB yet Also possible is that you're using a an MVCC DB such as Postgres or Oracle, and you're looking at an old, pre-update version of the data, as your direct SQL would be in a separate transaction --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
On Wed, Apr 30, 2008 at 10:56 AM, Rick Morrison [EMAIL PROTECTED] wrote: then queried the db directly using sql. It looks like the change hasn't made it to the DB yet Also possible is that you're using a an MVCC DB such as Postgres or Oracle, and you're looking at an old, pre-update version of the data, as your direct SQL would be in a separate transaction We are using Postgres (8.1.6), but in the case of the sqlalchemy code I've got transactional set to off for the session. I'm not too familiar with the specifics of MVCC (just had to google it, actually)...is it possible the new data isn't visible to the other process if the updating process still has a cursor live? -- david bonner [EMAIL PROTECTED] --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
On Wed, Apr 30, 2008 at 9:29 AM, Michael Bayer [EMAIL PROTECTED] wrote:
after_update() is called after all UPDATE statements have been issued
for that particular mapper. This includes *only* the table that is
mapped by that mapper, not any other mappers.
Is it possible that you are seeing an UPDATE being issued for an item
that is related to your parent via a many-to-one ? Or that you have
multiple ME's with after_update() at play and perhaps you're seeing a
different one fire off.
It was, but I've managed to reproduce the problem with a fairly
minimal test case:
import pdb
import datetime
import pprint
from pkg_resources import require
require('SQLAlchemy==0.4.3')
from sqlalchemy import *
from sqlalchemy.orm import *
class MyExtension (MapperExtension) :
def after_update (self, mapper, connection, instance) :
#pdb.set_trace()
pprint.pprint(instance)
return EXT_CONTINUE
class Schedule (object) : pass
dburl = 'postgres://names have been changed to protect the innocent'
engine = create_engine(dburl, strategy='threadlocal')
meta = MetaData(engine)
Session = scoped_session(sessionmaker(bind=engine,
autoflush=False,
transactional=False))
mapper = Session.mapper
meta.reflect()
mapper(Schedule, meta.tables['schedules'], extension=MyExtension())
s = Schedule.query.first()
s.notes = str(datetime.datetime.now())
Session.flush([s])
When this code drops me into pdb, the data in instance.notes looks
like the new value, but querying the db in a separate process gets me
the old value.
--
david bonner
[EMAIL PROTECTED]
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[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
I suppose that depends on the behavior of the DB-API interface, in this case I guess that's psycopg. Anyway, I'm certainly not sure if an MVCC snapshot that's causing your problem, but it does seem like at least a possibility. The certain way is to check the update status inside the same transaction that did the update -- in general you can't count on transaction B to see transaction A changes unless B starts after A commits. Whether an open pyscopg cursor implies an open transaction -- beats me. Rick --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
oops, uncommenting the pdb.set_trace(), obviously. sorry. class MyExtension (MapperExtension) : def after_update (self, mapper, connection, instance) : #pdb.set_trace() pprint.pprint(instance) return EXT_CONTINUE -- david bonner [EMAIL PROTECTED] --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
On Apr 30, 2008, at 11:22 AM, David Bonner wrote: When this code drops me into pdb, the data in instance.notes looks like the new value, but querying the db in a separate process gets me the old value. flush() always uses a transaction, so when your pdb process hits, the transaction has not been committed yet and results are not visible outside of the transaction. the transactional keyword on Session does not mean don't use transactions at all, it means don't automatically enter a transaction outside of a flush. Its been renamed to autocommit in 0.5. --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
On Wed, Apr 30, 2008 at 11:30 AM, Michael Bayer [EMAIL PROTECTED] wrote: flush() always uses a transaction, so when your pdb process hits, the transaction has not been committed yet and results are not visible outside of the transaction. the transactional keyword on Session does not mean don't use transactions at all, it means don't automatically enter a transaction outside of a flush. Its been renamed to autocommit in 0.5. Ah, yeah, that would do it. Any suggestions for other hooks that might do what I'm looking for, or should I just handle this myself before and after the flush? -- david bonner [EMAIL PROTECTED] --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
On Apr 30, 2008, at 12:15 PM, David Bonner wrote: On Wed, Apr 30, 2008 at 11:30 AM, Michael Bayer [EMAIL PROTECTED] wrote: flush() always uses a transaction, so when your pdb process hits, the transaction has not been committed yet and results are not visible outside of the transaction. the transactional keyword on Session does not mean don't use transactions at all, it means don't automatically enter a transaction outside of a flush. Its been renamed to autocommit in 0.5. Ah, yeah, that would do it. Any suggestions for other hooks that might do what I'm looking for, or should I just handle this myself before and after the flush? if you want pre/post flush activities theres a SessionExtension which hooks into Session for that. You can set it up with the sessionmaker() function so that its always plugged in. --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] Re: is MapperExtension.after_update() called before the UPDATE is issued to the DB?
On Wed, Apr 30, 2008 at 2:50 PM, Michael Bayer [EMAIL PROTECTED] wrote: if you want pre/post flush activities theres a SessionExtension which hooks into Session for that. You can set it up with the sessionmaker() function so that its always plugged in. thanks, i'll look into that. and thanks again for the amazingly-quick and helpful replies. -- david bonner [EMAIL PROTECTED] --~--~-~--~~~---~--~~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
