from sqlalchemy import MetaData,Table,Column,Integer,String,ForeignKey
from sqlalchemy.orm import mapper,relationship,create_session
import sets
# this example illustrates a polymorphic load of two classes
metadata = MetaData('sqlite://')
metadata.bind.echo = True
# 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))
)
metadata.create_all()
# 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")
})
session = create_session()
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.flush()
session.expunge_all()
c = session.query(Company).get(1)
for e in c.employees:
print e, e._sa_instance_state.key, e.company
assert sets.Set([e.name for e in c.employees]) == sets.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.flush()
session.expunge_all()
c = session.query(Company).get(1)
for e in c.employees:
print e
session.delete(c)
session.flush()
metadata.drop_all()
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