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"""Single-table inheritance example."""
from sqlalchemy import MetaData, Table, Column, Integer, String, \
ForeignKey, create_engine
from sqlalchemy.orm import mapper, relationship, sessionmaker
metadata = MetaData()
# a table to store companies
companies = Table('companies', metadata,
Column('company_id', Integer, primary_key=True),
Column('name', String(50)))
employees_table = Table('employees', metadata,
Column('employee_id', Integer, primary_key=True),
Column('company_id', Integer, ForeignKey('companies.company_id')),
Column('name', String(50)),
Column('type', String(20)),
Column('status', String(20)),
Column('engineer_name', String(50)),
Column('primary_language', String(50)),
Column('manager_name', String(50))
)
class Person(object):
def __init__(self, **kwargs):
for key, value in kwargs.items():
setattr(self, key, value)
def __repr__(self):
return "Ordinary person %s" % self.name
class Engineer(Person):
def __repr__(self):
return "Engineer %s, status %s, engineer_name %s, "\
"primary_language %s" % \
(self.name, self.status,
self.engineer_name, self.primary_language)
class Manager(Person):
def __repr__(self):
return "Manager %s, status %s, manager_name %s" % \
(self.name, self.status, self.manager_name)
class Company(object):
def __init__(self, **kwargs):
for key, value in kwargs.items():
setattr(self, key, value)
def __repr__(self):
return "Company %s" % self.name
person_mapper = mapper(Person, employees_table,
polymorphic_on=employees_table.c.type,
polymorphic_identity='person')
manager_mapper = mapper(Manager, inherits=person_mapper,
polymorphic_identity='manager')
engineer_mapper = mapper(Engineer, inherits=person_mapper,
polymorphic_identity='engineer')
mapper(Company, companies, properties={
'employees': relationship(Person, lazy=True, backref='company')
})
engine = create_engine('sqlite:///', echo=True)
metadata.create_all(engine)
session = sessionmaker(engine)()
c = Company(name='company1')
c.employees.append(Manager(name='pointy haired boss', status='AAB',
manager_name='manager1'))
c.employees.append(Engineer(name='dilbert', status='BBA',
engineer_name='engineer1', primary_language='java'))
c.employees.append(Person(name='joesmith', status='HHH'))
c.employees.append(Engineer(name='wally', status='CGG',
engineer_name='engineer2', primary_language='python'
))
c.employees.append(Manager(name='jsmith', status='ABA',
manager_name='manager2'))
session.add(c)
session.commit()
c = session.query(Company).get(1)
for e in c.employees:
print(e, e.company)
print("\n")
dilbert = session.query(Person).filter_by(name='dilbert').one()
dilbert2 = session.query(Engineer).filter_by(name='dilbert').one()
assert dilbert is dilbert2
dilbert.engineer_name = 'hes dibert!'
session.flush()
session.expunge_all()
c = session.query(Company).get(1)
for e in c.employees:
print(e)
session.delete(c)
session.commit()
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