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"""Single-table (table-per-hierarchy) inheritance example."""
from sqlalchemy import Column, Integer, String, \
ForeignKey, create_engine, inspect, or_
from sqlalchemy.orm import relationship, Session, with_polymorphic
from sqlalchemy.ext.declarative import declarative_base, declared_attr
Base = declarative_base()
class Company(Base):
__tablename__ = 'company'
id = Column(Integer, primary_key=True)
name = Column(String(50))
employees = relationship(
"Person",
back_populates='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(ForeignKey('company.id'))
name = Column(String(50))
type = Column(String(50))
company = relationship("Company", back_populates="employees")
__mapper_args__ = {
'polymorphic_identity': 'person',
'polymorphic_on': type
}
def __repr__(self):
return "Ordinary person %s" % self.name
class Engineer(Person):
engineer_name = Column(String(30))
primary_language = Column(String(30))
# illustrate a single-inh "conflicting" column declaration;
# see http://docs.sqlalchemy.org/en/latest/orm/extensions/
# declarative/inheritance.html#resolving-column-conflicts
@declared_attr
def status(cls):
return Person.__table__.c.get('status', 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):
manager_name = Column(String(30))
@declared_attr
def status(cls):
return Person.__table__.c.get('status', 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])
print(
session.query(eng_manager).
filter(
or_(
eng_manager.Engineer.engineer_name == 'engineer1',
eng_manager.Manager.manager_name == 'manager2'
)
).all()
)
# illustrate join from Company,
eng_manager = with_polymorphic(Person, [Engineer, Manager])
print(
session.query(Company).
join(
Company.employees.of_type(eng_manager)
).filter(
or_(eng_manager.Engineer.engineer_name == 'engineer1',
eng_manager.Manager.manager_name == 'manager2')
).all())
session.commit()
|
