Release: 1.0.0 | Release Date: Not released

SQLAlchemy 1.0 Documentation

Source code for examples.inheritance.joined

"""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()