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"""table_per_related.py
The HasAddresses mixin will provide a new "address" table for
each parent class, as well as a distinct "Address" subclass.
This configuration has the advantage that each type of parent
maintains its "Address" rows separately, so that collection
size for one type of parent will have no impact on other types
of parent. Navigation between parent and "Address" is simple,
direct, and bidirectional.
"""
from sqlalchemy.ext.declarative import declarative_base, declared_attr
from sqlalchemy import create_engine, Integer, Column, String, ForeignKey
from sqlalchemy.orm import Session, relationship
class Base(object):
"""Base class which provides automated table name
and surrogate primary key column.
"""
@declared_attr
def __tablename__(cls):
return cls.__name__.lower()
id = Column(Integer, primary_key=True)
Base = declarative_base(cls=Base)
class Address(object):
"""Define columns that will be present in each
'Address' table.
This is a declarative mixin, so additional mapped
attributes beyond simple columns specified here
should be set up using @declared_attr.
"""
street = Column(String)
city = Column(String)
zip = Column(String)
def __repr__(self):
return "%s(street=%r, city=%r, zip=%r)" % \
(self.__class__.__name__, self.street,
self.city, self.zip)
class HasAddresses(object):
"""HasAddresses mixin, creates a new Address class
for each parent.
"""
@declared_attr
def addresses(cls):
cls.Address = type(
"%sAddress" % cls.__name__,
(Address, Base,),
dict(
__tablename__ = "%s_address" %
cls.__tablename__,
parent_id = Column(Integer,
ForeignKey("%s.id" % cls.__tablename__)),
parent = relationship(cls)
)
)
return relationship(cls.Address)
class Customer(HasAddresses, Base):
name = Column(String)
class Supplier(HasAddresses, Base):
company_name = Column(String)
engine = create_engine('sqlite://', echo=True)
Base.metadata.create_all(engine)
session = Session(engine)
session.add_all([
Customer(
name='customer 1',
addresses=[
Customer.Address(
street='123 anywhere street',
city="New York",
zip="10110"),
Customer.Address(
street='40 main street',
city="San Francisco",
zip="95732")
]
),
Supplier(
company_name="Ace Hammers",
addresses=[
Supplier.Address(
street='2569 west elm',
city="Detroit",
zip="56785")
]
),
])
session.commit()
for customer in session.query(Customer):
for address in customer.addresses:
print(address)
print(address.parent)
|
