Yes, a nice simplification.
I'm using it to lazyload attributes for objects that aren't in a
session. I'm not sure if you pointed me there, I think I found it
myself, but you helped work out the later details...
Our app lives inside a webserver framework that, very appropriately,
in my opinion, only has one session for any given web request. So,
for our framework, I can safely lazyload related attributes for
transient or detached objects by temporarily setting state.session_id:
def configure_attribute(class_, attr, inst):
"""
Set up function to be invoked when relations are 'get'ed on
possibly
transient objects, so we can automatically query these related
objects
"""
if isinstance(inst.property, RelationshipProperty):
default_loader = inst.impl.callable_
def load_value(state, passive):
if state.session_id is not None:
# this is persistent or pending, so
# return default sqla functionality
return default_loader(state, passive)
if passive is attributes.PASSIVE_NO_FETCH:
return attributes.PASSIVE_NO_RESULT
# session_id is currently None
state.session_id = DBSession().hash_key
retval = default_loader(state, passive)
state.session_id = None
return retval
inst.impl.callable_ = load_value
..
..
event.listen(DBEntity, 'attribute_instrument', configure_attribute)
On Dec 26, 12:26 pm, Michael Bayer <mike...@zzzcomputing.com> wrote:
> On Dec 26, 2011, at 9:07 AM, Kent wrote:
>
> > Documentation for AttributeImpl.callable_ still reads
> > "optional function which generates a callable based on a parent
> > instance, which produces the "default" values for a scalar or
> > collection attribute when it's first accessed, if not present
> > already."
> > But it seems it is no longer the function which generates a callable, but
> > rather is the callable itself now, accepting both the state and the passive
> > parameters.
>
> > It used to be two stages, first callable_ accepts a state and then that
> > returns a callable which accepted the passive parameter.
>
> yes that was a fabulous simplification of things I'm still very happy about.
>
>
>
> > Can you briefly summarize how this is meant to work now? (I think the doc
> > string is wrong now??)
>
> docstring is wrong yes. the callable just receives a state and a passive
> flag, then loads something for the attribute. It's just one less level of
> "callable" and the two that we have in use are LoadDeferredColumns and
> LoadLazyAttribute in strategies.py. This also isn't very public API and
> if I pointed you to this for some previous issue, I'd be curious if I
> remembered to mention that.....
>
>
>
>
>
>
>
>
>
> > On 12/25/2011 10:31 AM, Michael Bayer wrote:
>
> >> yes a few change names, reconstruct_instance, init_instance, init_failed.
>
> >> On Dec 24, 2011, at 7:42 PM, Kent Bower wrote:
>
> >>> Right. And reconstruct_instance() was renamed load()?
>
> >>> On 12/24/2011 5:56 PM, Michael Bayer wrote:
> >>>> On Dec 24, 2011, at 10:04 AM, Kent wrote:
>
> >>>>> As the migration guide suggests, I'd like to embrace the events API.
> >>>>> Is mapper event load() invoked at exactly the same place as the
> >>>>> deprecated reconstruct_instance() ?
> >>>> yeah nothing has been moved. All the places where the internals would
> >>>> call XXXExtension.xxx_event() were just replaced with
> >>>> self.dispatch.xxx_event(), and the old Extension classes are invoked via
> >>>> an adapter to the new system. All unit tests for the extension system
> >>>> remain in place and haven't been modified.
>
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