On Jul 11, 2010, at 9:56 AM, Nikolaj wrote:
> Ah, it's pretty clear why this happens in Mapper.__init__:
>
> self._configure_extensions()
> self._configure_class_instrumentation()
> self._configure_properties()
>
> Should MapperExtensions that want to extend properties mess with
> mapper._init_properties instead?
for a recipe that adds AttributeExtensions in a generic way, see the example
examples/custom_attributes/listen_for_events.py .
You can install the __sa_instrumentation_manager__ attribute in the
MapperExtension.instrument_class step if you prefer.
>
> On Jul 11, 2:49 pm, Nikolaj <nik....@gmail.com> wrote:
>> I was trying to add an AttributeExtension to a property from my
>> MapperExtension but I get this error when trying to access the
>> property:
>>
>> AttributeError: 'Mapper' object has no attribute '_props'
>>
>> Here's a test case:
>>
>> from sqlalchemy import create_engine, Column
>> from sqlalchemy.ext.declarative import declarative_base
>> from sqlalchemy.types import Integer, String
>> from sqlalchemy.orm import scoped_session, sessionmaker, deferred
>> from sqlalchemy.orm.interfaces import MapperExtension
>>
>> engine = create_engine('sqlite:///:memory:', echo=True)
>> Base = declarative_base(bind=engine)
>>
>> class MyExtension(MapperExtension):
>> def __init__(self, property):
>> self.property = property
>>
>> def instrument_class(self, mapper, class_):
>> property = mapper.get_property(self.property)
>> print property
>>
>> class Item(Base):
>> __tablename__ = 'items'
>> __mapper_args__ = {'extension': MyExtension('name')}
>>
>> id = Column(Integer, primary_key=True)
>> name = deferred(Column(String))
>
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