I’d like to pick up this topic once more briefly.
Suppose I get the “new”, “dirty”, and “deleted” sets as per discussion
below, and I’m especially interested in the “dirty” set: is there a way to
find out which properties of an object were modified, or only that the
object was modified?
Thanks!
Jens
On Wednesday, November 22, 2017 at 9:46:54 AM UTC+10, jens.t...@gmail.com
wrote:
>
> Thank you, the event worked like a charm :-) Though I think that I don't
> need the commit events, because the application terminates anyway.
>
> I modified your approach to gather which objects were flushed so that in
> the end I can give the user more precise information:
>
> dbsession.info["new"] = set()
>
> dbsession.info["dirty"] = set()
>
> dbsession.info["deleted"] = set()
>
>
>
> def update_session_info(session):
>
> new = session.info["new"]
>
> new |= set(session.new)
>
> dirty = session.info["dirty"]
>
> dirty |= set(session.dirty)
>
> deleted = session.info["deleted"]
>
> deleted |= set(session.deleted)
>
> return new, dirty, deleted
>
>
>
> @event.listens_for(dbsession, "before_flush")
>
> def on_before_flush(session, _, _):
>
> update_session_info(session)
>
> ...
> code.interact(local=locals())
>
> ...
>
> new, dirty, deleted = update_session_info(dbsession)
>
> if new or dirty or deleted:
>
> if new:
>
> print("The following objects were created: ", new)
>
> if dirty:
>
> print("The following objects were modified: ", dirty)
>
> if deleted:
>
> print("The following objects were deleted: ", deleted)
>
> yesno = input("Would you like to commit this transaction?
> [y/N] ")
> if yesno == "y":
>
> print("Committing transaction...")
>
> else:
>
> print("Rolling back transaction...")
>
> raise _SessionRollbackException()
>
>
> # ...this is where the context closes and the transaction commits
> and the dbsession ends.
>
> Cheers,
> Jens
>
>
>
> On Saturday, November 18, 2017 at 12:03:05 AM UTC+10, Simon King wrote:
>>
>> OK, I think tracking session events seems reasonable. You could do
>> something like this (completely untested):
>>
>> from sqalchemy.event import event
>>
>> @event.listens_for(YourSessionOrSessionMaker, 'before_flush')
>> def on_before_flush(session, flush_context, instances):
>> session.info['flushed'] = True
>>
>>
>> # You'd probably also want to reset the 'flushed' flag
>> # after a commit or rollback
>> @event.listens_for(YourSessionOrSessionMaker, 'after_commit')
>> @event.listens_for(YourSessionOrSessionMaker, 'after_rollback')
>> def on_session_reset(session):
>> session.info['flushed'] = False
>>
>>
>> # when user exits interactive session:
>> modified = (
>> session.info.get('flushed', False)
>> or session.deleted
>> or session.new
>> or session.dirty
>> )
>> if modified:
>> raw_input('do you want to commit?')
>>
>>
>> ...but note that if you ever execute raw SQL (ie.
>> session.execute('UPDATE x WHERE y')), that will not be noticed by
>> those events.
>>
>> Hope that helps,
>>
>> Simon
>>
>
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