Manually mapping class inheritance hierarchies is laborious and not something I'd recommend, but here goes. Start by defining your table. Since using single table inheritance, it must include all the required columns:
metadata = MetaData()
employee = Table(
'employee',
metadata,
Column('id', Integer, primary_key=True),
Column('name', String(50)),
Column('type', String(20)),
Column('manager_data', String(50)),
Column('engineer_info', String(50))
)
The plain Python classes:
class Employee:
def __init__(self, name):
self.name = name
class Manager(Employee):
def __init__(self, name, manager_data):
super().__init__(name)
self.manager_data = manager_data
class Engineer(Employee):
def __init__(self, name, engineer_info):
super().__init__(name)
self.engineer_info = engineer_info
And the classical mappings:
mapper(Employee, employee,
polymorphic_on=employee.c.type,
polymorphic_identity='employee',
exclude_properties={'engineer_info', 'manager_data'})
mapper(Manager,
inherits=Employee,
polymorphic_identity='manager',
exclude_properties={'engineer_info'})
mapper(Engineer,
inherits=Employee,
polymorphic_identity='engineer',
exclude_properties={'manager_data'})
Note how you have to limit the mapped properties manually in each mapper, which will become hard to maintain with larger hierarchies. When using Declarative all that is handled for you.
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