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

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