On 10/13/2010 10:55 AM, Christophe de Vienne wrote:
Hi all,
I am running into an issue with MapperExtension.[before|after]_update.
Context
-------
SQLAlchemy 0.5.8
TurboGears 1.1.1
Description
-----------
I will attempt a simple description first, as I don't think my actual
code will help (I know it is not a thing to say, but really).
We have 2 mapped classes, Parent and Child.
Child is mapped this way :
mapper(Child, child_table, properties={
parent=relation(Parent, backref='children')
})
And parent has a mapperextension that defines a after_update :
def after_update(self, mapper, connection, instance):
for child in instance.children:
child.name = 'another name'
If I do 2 session flush() after modifying a Parent instance, the
modifications on the children should be reflected to the database.
It is the case in my unit tests if I use directly the DBSession and
manipulate the objects 'myself'.
BUT, if I go through the complete TG stack, in the unittests or in
real-life, the modifications done on child are never sent to the database.
One subtle thing though : if, before the first flush(), I access the
children attribute, the problem goes away.
Example :
parent = DBSession.query(Parent).get('myid')
parent.name = 'test'
# parent.children # Un-commenting this line solve the issue, but of
# course it is not an acceptable solution
DBSession.flush()
DBSession.flush()
I could not reproduce in a simpler context, and don't know how to go
further in my investigation.
Help ?
Thanks
Christophe
AFAIK SQLAlchemy does not support the following in MapperExtensions:
* lazy-loading related objects (maybe?)
* changing the "flush plan", which I believe means changing which
objects are considered new, dirty, or deleted
Your code is possibly trying to do both. You need to instead create a
SessionExtension and override before_flush, which allows you to modify
the session however you want, e.g. (untested):
class MySessionExtension(object):
def before_flush(self, session, flush_context, instances):
for obj in session.dirty:
if isinstance(obj, Parent):
for child in obj.children:
child.name = 'another name'
-Conor
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