Hi,
I'm trying to create a custom/derived attribute on a table class. This
is what I have defined:
class Plate(Base):
__tablename__ = 'plate'
__table_args__ = {'autoload' : True}
class Design(Base):
__tablename__ = 'design'
__table_args__ = {'autoload' : True}
class Pointing(Base):
__tablename__ = 'design'
__table_args__ = {'autoload' : True}
I then map these together:
Plate.design = relation(Design, primaryjoin=Plate.design_pk ==
Design.pk, backref="plate")
Design.pointings = relation(Pointing,
primaryjoin=Design.pk ==
Pointing.design_pk,
backref="design")
(So a plate has one design, and a design can have multiple pointings.
Sorry for the jargon.)
All of this works. I'd like to be able to write a convenience method
to access data in "plugging" directly from "plate", for example,
instead of doing:
plate.design.pointings[0].center_ra
I'd like to be able to say:
plate.ra
How can I create this attribute? I've tried something like:
Plate.ra = column_property(Plate.__table__.design.pointings
[0].center_ra)
but I get:
AttributeError: 'Table' object has no attribute 'design'
For extra credit, is it possible to write a method on Plate that I can
use like this?
plugging_no = 0
plate.ra(plugging_no)
It's easy to do these things in the Plate class definition, but at the
time I define it the other classes/tables are not defined (nor the
mappings).
Cheers,
Demitri
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