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"""Joined-table (table-per-subclass) inheritance example."""
from sqlalchemy import Table, Column, Integer, String, \
ForeignKey, create_engine, inspect, or_
from sqlalchemy.orm import relationship, Session, with_polymorphic
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Company(Base):
__tablename__ = 'company'
id = Column(Integer, primary_key=True)
name = Column(String(50))
employees = relationship("Person",
backref='company',
cascade='all, delete-orphan')
def __repr__(self):
return "Company %s" % self.name
class Person(Base):
__tablename__ = 'person'
id = Column(Integer, primary_key=True)
company_id = Column(Integer, ForeignKey('company.id'))
name = Column(String(50))
type = Column(String(50))
__mapper_args__ = {
'polymorphic_identity':'person',
'polymorphic_on':type
}
def __repr__(self):
return "Ordinary person %s" % self.name
class Engineer(Person):
__tablename__ = 'engineer'
id = Column(Integer, ForeignKey('person.id'), primary_key=True)
status = Column(String(30))
engineer_name = Column(String(30))
primary_language = Column(String(30))
__mapper_args__ = {
'polymorphic_identity':'engineer',
}
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):
__tablename__ = 'manager'
id = Column(Integer, ForeignKey('person.id'), primary_key=True)
status = Column(String(30))
manager_name = Column(String(30))
__mapper_args__ = {
'polymorphic_identity':'manager',
}
def __repr__(self):
return "Manager %s, status %s, manager_name %s" % \
(self.name, self.status, self.manager_name)
engine = create_engine('sqlite://', echo=True)
Base.metadata.create_all(engine)
session = Session(engine)
c = Company(name='company1', employees=[
Manager(
name='pointy haired boss',
status='AAB',
manager_name='manager1'),
Engineer(name='dilbert',
status='BBA',
engineer_name='engineer1',
primary_language='java'),
Person(name='joesmith'),
Engineer(name='wally',
status='CGG',
engineer_name='engineer2',
primary_language='python'),
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, inspect(e).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 dilbert!'
session.commit()
c = session.query(Company).get(1)
for e in c.employees:
print(e)
# query using with_polymorphic.
eng_manager = with_polymorphic(Person, [Engineer, Manager], aliased=True)
print(session.query(eng_manager).\
filter(
or_(eng_manager.Engineer.engineer_name=='engineer1',
eng_manager.Manager.manager_name=='manager2'
)
).all())
# illustrate join from Company,
# We use aliased=True
# to help when the selectable is used as the target of a join.
eng_manager = with_polymorphic(Person, [Engineer, Manager], aliased=True)
print(session.query(Company).\
join(
eng_manager,
Company.employees
).filter(
or_(eng_manager.Engineer.engineer_name=='engineer1',
eng_manager.Manager.manager_name=='manager2')
).all())
session.commit()
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