This is the way I solved the problem... (how to backup a table row into
another table before delete or update it) ...if it can help:
from sqlalchemy.orm import MapperExtension
class History(MapperExtension):
def __init__(self):
MapperExtension.__init__(self)
self.methods = ('before_update','before_delete')
def clone(self, mapper, connection, instance, action):
tablename=mapper.mapped_table.name
tablename_bak=tablename+'_bak'
rec = connection.execute(select([tbl[tablename]], tbl[tablename].c.id ==
getattr( instance, '%s_id'%tablename))).fetchone()
dd=dict()
modified=False
for k,v in rec.items():
dd[ k.lower() ] = v
if action=='D': #if delete request...
connection.execute(tbl[tablename_bak].insert(values=dd))
elif action=='U': #if update request...
for k in instance.c: #check for differences, to save it only if it was
modified...
if getattr( instance,str(k).replace('.','_')) != dd[str(k).split('.')[1]]:
modified=True
break
if modified is True:
connection.execute(tbl[tablename_bak].insert(values=dd))
return
def before_update(self, mapper, connection, instance):
return self.clone(mapper, connection, instance, 'U')
def before_delete(self, mapper, connection, instance):
return self.clone(mapper, connection, instance, 'D')
I call it in this way:
from ... import History
mapper(Anagrafica,
tbl['anagrafica'],
column_prefix = 'anagrafica_',
extension=History(),
)
Paddy Mullen wrote:
I have been trying to create a nice decorator for tasks that are
methods of models. I want the tasks to run after specific conditions
(after_update/insert, with predicates).
I was able to set this up through a series of event hooks starting
with "mapper_configured".
The problem I have run into is, listening for "after_insert" on a
subclass extending DeclarativeBase, only results in calls after insert
has been called for, but not after it has been executed. I can listen
on the engine to "after_execute", which does seem to give a callback
after commit/flush has actually been called, but at this I have no
declarativeBase references to the objects that have been inserted,
only to the raw sql.
Am I missing something?
Here are the example files
https://github.com/paddymul/sqlalchemy_garden/blob/master/lib/deferred_task.py
- the library
https://github.com/paddymul/sqlalchemy_garden/blob/master/schemas/deferred_schema.py
- an example usage
Thanks,
Paddy
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