On Apr 9, 2007, at 11:25 AM, Brendan Arnold wrote:
> Is there a way I can ensure that an empty instance of my Address
> object is grafted onto the Person object even when corresponding data
> is not found in the people table?
you can either create a layer of abstraction between the actual
mapped property and the publically accessible field by using a property:
class User(object):
def _get_address(self):
if self._address is None:
self._address = Address()
return self._address
address = property(_get_address)
mapper(User, users, properties={"_address":relation(Address)})
or you can use a MapperExtension and override create_instance():
class MyExt(MapperExtension):
def create_instance(self, mapper, selectcontext, row, class_):
instance = User()
if not row['address_id']:
instance.address = Address()
return instance
mapper(User, users, properties=..., extension=MyExt())
in both cases, flushing the User object will create a new address row
in the DB since you have the blank address object there...to avoid
that, you might have to add more layers of abstraction to the public
"address" property.
of course theres another view of this, which is why does your
application prefer a "blank" Address entry to None? the latter is
more semantically correct.
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