I have a single table that looks similar to the following:
class Equipment(Base):
type = Column(CHAR(1), primary_key=True)
sub_type = Column(CHAR(1), primary_key=True)
code = Column(CHAR(5), primary_key=True)
For historical purposes, I cannot modify this table. I would like to setup
multi-level inheritance similar to this, however it does not work:
class Equipment(Base):
type = Column(CHAR(1), primary_key=True)
sub_type = Column(CHAR(1), primary_key=True)
code = Column(CHAR(5), primary_key=True)
__mapper_args__ = {'polymorphic_on': type}
class Vehicle(Equipment):
__mapper_args__ = {'polymorphic_identity': 'V', 'polymorphic_on':
sub_type}
class Bus(Vehicle)
__mapper_args__ = {'polymorphic_identity': 'B'}
class Rail(Vehicle)
__mapper_args__ = {'polymorphic_identity': 'R'}
I can concatenate the multiple column values into a single discriminator
column_property but then I do not have an easy way to retrieve all vehicles.
Any ideas?
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