examples.inheritance.concrete — SQLAlchemy 1.0 Documentation

Release: 1.0.14 | Release Date: July 6, 2016

# SQLAlchemy 1.0 Documentation

# Source code for examples.inheritance.concrete

    """Concrete (table-per-class) inheritance example."""

    from sqlalchemy import create_engine, MetaData, Table, Column, Integer, \
        String
    from sqlalchemy.orm import mapper, sessionmaker, polymorphic_union

    metadata = MetaData()

    managers_table = Table('managers', metadata,
        Column('employee_id', Integer, primary_key=True),
        Column('name', String(50)),
        Column('manager_data', String(40))
    )

    engineers_table = Table('engineers', metadata,
        Column('employee_id', Integer, primary_key=True),
        Column('name', String(50)),
        Column('engineer_info', String(40))
    )

    engine = create_engine('sqlite:///', echo=True)
    metadata.create_all(engine)

    class Employee(object):
        def __init__(self, name):
            self.name = name
        def __repr__(self):
            return self.__class__.__name__ + " " + self.name

    class Manager(Employee):
        def __init__(self, name, manager_data):
            self.name = name
            self.manager_data = manager_data
        def __repr__(self):
            return self.__class__.__name__ + " " + \
                        self.name + " " +  self.manager_data

    class Engineer(Employee):
        def __init__(self, name, engineer_info):
            self.name = name
            self.engineer_info = engineer_info
        def __repr__(self):
            return self.__class__.__name__ + " " + \
                        self.name + " " +  self.engineer_info

    pjoin = polymorphic_union({
        'manager':managers_table,
        'engineer':engineers_table
    }, 'type', 'pjoin')

    employee_mapper = mapper(Employee, pjoin, polymorphic_on=pjoin.c.type)
    manager_mapper = mapper(Manager, managers_table,
                            inherits=employee_mapper, concrete=True,
                            polymorphic_identity='manager')
    engineer_mapper = mapper(Engineer, engineers_table,
                             inherits=employee_mapper, concrete=True,
                             polymorphic_identity='engineer')

    session = sessionmaker(engine)()

    m1 = Manager("pointy haired boss", "manager1")
    e1 = Engineer("wally", "engineer1")
    e2 = Engineer("dilbert", "engineer2")

    session.add(m1)
    session.add(e1)
    session.add(e2)
    session.commit()

    print(session.query(Employee).all())