Tomasz Jezierski - Tefnet wrote:
>
> Awkward column_property is because of exception you'll get if try to set
> Column without column_proprerty around it:
> ---
> sqlalchemy.exc.ArgumentError: Column 'PhysObject.locationId' is not
> represented in mapper's table. Use the `column_property()` function to
> force this column to be mapped as a read-only attribute.
If you keep the mapping straightforward and create attributes for each
column distinctly, all relationships can be correctly established using
documented patterns. I don't really know what issues your approach is
having since I tend to focus on the working example, which is below.
Adapt it to your custom metaclass one step at a time...though i feel
keeping the mappings explicit and declarative leads to better results.
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class TefObject(Base):
__tablename__ = "TefObject"
Id = Column( Integer, primary_key=True,autoincrement=True)
objectType = Column( String(128),nullable=False)
__mapper_args__ = {'polymorphic_on': objectType,
'polymorphic_identity':"TefObject"}
class PhysObject(TefObject):
__tablename__ = "PhysObject"
phys_id = Column("Id", Integer,ForeignKey(TefObject.Id),
primary_key=True)
barCode = Column( String(12),nullable=False)
locationId = Column(Integer, ForeignKey('Location.Id', name =
'physobject_location_fkey', use_alter = True))
location = relation("Location",
primaryjoin="PhysObject.locationId==Location.location_id",
remote_side="Location.location_id"
)
__mapper_args__ = {'polymorphic_identity':"PhysObject",
"inherit_condition":phys_id==TefObject.Id}
class Location(PhysObject):
__tablename__ = "Location"
location_id = Column("Id", Integer,ForeignKey(PhysObject.phys_id),
primary_key=True)
description = Column( String(128))
__mapper_args__ = {'polymorphic_identity':"Location",
"inherit_condition":location_id==PhysObject.phys_id}
if __name__ == '__main__':
engine = create_engine('sqlite://', echo=True)
Base.metadata.create_all(engine)
session = sessionmaker(engine)()
room = Location(description = 'room 1', barCode = '1234')
desk = PhysObject(barCode='555', location = room)
session.add(room)
session.add(desk)
session.commit()
for t in session.query(TefObject):
print t, getattr(t, "location", None)
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