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from sqlalchemy import MetaData, Table, Column, Integer, String, \
ForeignKey, create_engine
from sqlalchemy.orm import mapper, relationship, sessionmaker
# this example illustrates a polymorphic load of two classes
metadata = MetaData()
# a table to store companies
companies = Table('companies', metadata,
Column('company_id', Integer, primary_key=True),
Column('name', String(50)))
# we will define an inheritance relationship between the table "people" and
# "engineers", and a second inheritance relationship between the table
# "people" and "managers"
people = Table('people', metadata,
Column('person_id', Integer, primary_key=True),
Column('company_id', Integer, ForeignKey('companies.company_id')),
Column('name', String(50)),
Column('type', String(30)))
engineers = Table('engineers', metadata,
Column('person_id', Integer, ForeignKey('people.person_id'),
primary_key=True),
Column('status', String(30)),
Column('engineer_name', String(50)),
Column('primary_language', String(50)),
)
managers = Table('managers', metadata,
Column('person_id', Integer, ForeignKey('people.person_id'),
primary_key=True),
Column('status', String(30)),
Column('manager_name', String(50))
)
# create our classes. The Engineer and Manager classes extend from Person.
class Person(object):
def __init__(self, **kwargs):
for key, value in kwargs.iteritems():
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.iteritems():
setattr(self, key, value)
def __repr__(self):
return "Company %s" % self.name
person_mapper = mapper(Person, people, polymorphic_on=people.c.type,
polymorphic_identity='person')
mapper(Engineer, engineers, inherits=person_mapper,
polymorphic_identity='engineer')
mapper(Manager, managers, inherits=person_mapper,
polymorphic_identity='manager')
mapper(Company, companies, properties={'employees'
: relationship(Person, lazy='joined', backref='company',
cascade='all, delete-orphan')})
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._sa_instance_state.key, e.company
assert set([e.name for e in c.employees]) == set(['pointy haired boss',
'dilbert', 'joesmith', 'wally', 'jsmith'])
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.commit()
c = session.query(Company).get(1)
for e in c.employees:
print e
# illustrate querying using direct table access:
print session.query(Engineer.engineer_name).\
select_from(engineers).\
filter(Engineer.primary_language=='python').\
all()
session.delete(c)
session.commit()
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