Hi,
Sorry for the last mail, which i sent in error, before finishing it.
If you(Michael) still have it in the filter, please just reject it.
I am working on a notification framework, which saves the dirty, new
and deleted states of objects in sessions to an Eventlog at commit
time.
The target is to have asynchronous agents listening to table changes
and a sqla extension to notify them when data is written to db.
The notification sender core code is written as a SessionExtension at
the moment.
The design uses the postgres NOTIFY / listen statements, and a table
(event_log) for carrying the per commit information of primary id's
which have added/deleted/modified. I know that NOTIFY is not sql
standard, but many dbs have some sort of notification capability. So i
think a general case is abstractable from this db agnostic proposal
(=pg's NOTIFY).
It is even conceivable to send the notification event through OS
services, while still keep the notification data in the db.
I have already implemented this simple protocol:
before_commit(self, session):
event_data=# get all pks for session.['dirty', 'new', 'deleted']
for each x of [dirty', 'new', 'deleted']
session.add(Event( data=event_data[x]))
session.add(Event(data=event_data)) # gener
for each object type:
for each notification type: #= one of (dirty', 'new', 'deleted')
self.pending_notifications = [self.get_table_name(class_)]
^^^^
First Question: How does SQLAlchemy map the call to
session.query(MappedObject) to a MetaData.tables[x]. Is there any way
to do this without using a custom mapper fuction ? I would prefer
using the same mechanism as SQLAlchemy
self.pending_notifications += General Event for table
after_commit:
send Notifications on separate db agnostic connection (in pg i need
to set a different isolation level)
My second concern is about what session.execute("UPDATE table_x set
pop = ''newval") actually does.
Is the sql statement parsed for table names? My interest would be in
marking the objects which are changed by this update as dirty. So what
i am really looking for is
a method to generate
Note that i use pk=Primary Key
'SELECT pk1, pk2 ...., change_field from tablename where prop=x'
from an update:
'UPDATE tablename set change_field=... where prop=x'
This would enable me to generate a dirty pk list from any (text) sql
statement accepted by sqla.
Please let me know if you feel that this design is not the 'sqla way
to do things'. I want to OS the code, but i wanted to get an short
feedback if this is of any use for anyone out there. So please
comment :)
paul
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