oh, 0.3. well theres another question. If you just converted from
SQLObject, why to SA 0.3 ? 0.4 is the currently supported version and
is also vastly superior to 0.3.
On Jan 30, 2008, at 2:40 PM, jason kirtland wrote:
>
> On 0.3.x, use EXT_PASS rather than EXT_CONTINUE.
>
> Michael Bayer wrote:
>> sorry, the docstring is wrong. create_instance() should return
>> EXT_CONTINUE if it would like to bypass creating the instance itself.
>> However, "self" here is the MapperExtension instance, not the mapped
>> instance. the method is called before anything is created.
>>
>> if you want to populate an attribute on a newly loaded instance but
>> not create it, you're better off using populate_instance(). return
>> EXT_CONTINUE from that method as well.
>>
>> class MyExt(MapperExtension):
>> def populate_instance(self, mapper, selectcontext, row, instance,
>> **flags):
>> if not hasattr(instance, 'mutex'):
>> instance.mutex = mutex()
>> return EXT CONTINUE
>>
>> the hasattr() is assuming you dont want to replace the mutex in the
>> case of a session.refresh() or similar.
>>
>> On Jan 30, 2008, at 1:36 PM, Ross wrote:
>>
>>> Hello,
>>>
>>> I have recently converted a Pylons app from SQLObject to SQLAlchemy
>>> 0.3.10. Conversion went quite well.
>>>
>>> I need to serialize access to some of my objects, so I've looked
>>> into
>>> extending MapperExtension as described at [1] to add a mutex on
>>> load.
>>>
>>> First, I define an extension and instantiate it:
>>> --------
>>> from sqlalchemy.orm import MapperExtension
>>> import mutex
>>>
>>> class MutexExtension(MapperExtension):
>>> def create_instance(self, mapper, selectcontext, row, class_):
>>> self.mutex = mutex.mutex()
>>> return None
>>>
>>> mutexext = MutexExtension()
>>> -------
>>>
>>>
>>> My mapper setup looks like this:
>>>
>>> switch_mapper = mapper (Switch, switch_table,
>>> extension=[mutexext.mutexext, sac.ext],
>>>
>>> properties={'ports':sqla.relation(SwitchPort)})
>>>
>>>
>>> When I try to fetch objects from the database, I get a exception
>>> setting
>>> self.entity_name:
>>>
>>>
>>> Module sqlalchemy.orm.mapper:1485 in _instance
>>> << instance =
>>> self._create_instance(context.session)
>>> else:
>>> instance._entity_name = self.entity_name
>>> if self.__should_log_debug:
>>> self.__log_debug("_instance(): created new
>>> instance %s identity %s" % (mapperutil.instance_str(instance),
>>> %str(identitykey)))>>
>>> instance._entity_name = self.entity_name
>>> exceptions.AttributeError: 'NoneType' object has no attribute
>>> '_entity_name'
>>>
>>>
>>> What did I do wrong?
>>>
>>> Thanks,
>>> Ross
>>>
>>>
>>>
>>>
>>> [1]
>>> http://www.sqlalchemy.org/docs/03/adv_datamapping.html#advdatamapping_extending
>>>
>>
>>
>>>
>
>
> >
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