address_table = sa.Table('address', metadata,
    sa.Column('addr_id', sa_types.Integer, primary_key=True),
    sa.Column('text', sa_types.Unicode),
    sa.Column('created', sa_types.DateTime, default=datetime.now),
    sa.Column('updated', sa_types.DateTime, default=datetime.now, onupdate=datetime.now),
)

class Address(object):
    def __init__(self, text=None, addr_id=None):
        self.text = text
        self.addr_id = addr_id

address_mapper = orm.mapper(Address, address_table)

class Person(DBObject):
    __tablename__ = 'person'
    #_primary_key_name = 'person_id'

    _shoji_attr_blacklist_ = {
        'body': ['ptype', 'baddr_id', 'maddr_id'],
        'catalogs': ['billing_address_record', 'mailing_address_record']
    }

    person_id = sa.Column(sa_types.Integer, primary_key=True)
    ptype = sa.Column(sa_types.String(10), nullable=False)
    fname = sa.Column(sa_types.Unicode(63))
    lname = sa.Column(sa_types.Unicode(63))
    mi    = sa.Column(sa_types.Unicode(5))
    dname = sa.Column(sa_types.Unicode(255)) #Display name
    maddr_id = sa.Column(sa_types.Integer, sa.ForeignKey('address.addr_id'))
    baddr_id = sa.Column(sa_types.Integer, sa.ForeignKey('address.addr_id'))
    created = sa.Column(sa_types.DateTime, default=datetime.now)
    updated = sa.Column(sa_types.DateTime, default=datetime.now, onupdate=datetime.now)

    #....

    # Has to show up below the definition of ptype
    __mapper_args__ = {
            'polymorphic_on': ptype,
            'polymorphic_identity': 'Person'
        }

    # association proxies
    mailing_address = association_proxy('mailing_address_record', 'text')
    billing_address = association_proxy('billing_address_record', 'text')