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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