...and I've figured out a workaround:
in Switch(Device):
pcs = relationship('PC', primaryjoin = 'Switch.mac ==
PC.switch_mac', lazy='dynamic')
Now, switch.pcs.count() works :)
S.
On Aug 4, 5:00 pm, Zippy P <[email protected]> wrote:
> I have a single-table inheritance setup:
>
> class Device(Base):
> __tablename__ = 'devices'
> devtype = Column(Unicode(20), nullable = False)
> mac = Column(Unicode(128), primary_key = True)
> ...
>
> class PC(Device):
> __mapper_args_ = {'polymorphic_identity':u'PC'}
> switch_mac = Column(Unicode(128), ForeignKey(mac), nullable = True) #
> ignore any typos here - this is munged code
>
> class Switch(Device):
> __mapper_args_ = {'polymorphic_identity':u'Switch'}
> ...
>
> pc_ct_subq = select([func.count(PC.mac)]).where(PC.switch_mac ==
> Switch.mac).as_scalar()
> Switch.pc_ct = column_property(pc_ct_subq)
>
> When I didn't have the inheritance set up (when Switch and PC were separate
> tables and separate objects), pc_ct worked fine. Now, however, it's failing
> - I think because the inheritance is appending "AND devices.devtype IN 'AP'"
> to the initial load query since it's trying to bring up just devices of type
> 'Switch'.
>
> How do I get around this? I just want Switch to have an attribute that
> represents the number of PCs that are associated to it (where the PC's
> switch_mac equals the Switch's mac).
>
> Thanks,
>
> S.
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