mirror of
https://github.com/sqlalchemy/sqlalchemy.git
synced 2026-06-01 05:18:44 -04:00
Mike Bayer
065fcbd9d2
relationship(), to eliminate confusion over the relational algebra term. relation() however will remain available in equal capacity for the foreseeable future. [ticket:1740]
154 lines
3.9 KiB
Python
154 lines
3.9 KiB
Python
"""
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"polymorphic" associations, ala SQLAlchemy.
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This example generalizes the function in poly_assoc_pk.py into a
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function "association" which creates a new polymorphic association
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"interface".
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"""
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from sqlalchemy import MetaData, Table, Column, Integer, String, ForeignKey
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from sqlalchemy.orm import mapper, relationship, create_session, class_mapper
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metadata = MetaData('sqlite://')
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def association(cls, table):
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"""create an association 'interface'."""
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interface_name = table.name
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attr_name = "%s_rel" % interface_name
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metadata = table.metadata
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association_table = Table("%s_associations" % interface_name, metadata,
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Column('assoc_id', Integer, primary_key=True),
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Column('type', String(50), nullable=False)
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)
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class GenericAssoc(object):
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def __init__(self, name):
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self.type = name
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def interface(cls, name, uselist=True):
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mapper = class_mapper(cls)
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table = mapper.local_table
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mapper.add_property(attr_name, relationship(GenericAssoc, backref='_backref_%s' % table.name))
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if uselist:
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# list based property decorator
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def get(self):
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if getattr(self, attr_name) is None:
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setattr(self, attr_name, GenericAssoc(table.name))
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return getattr(self, attr_name).targets
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setattr(cls, name, property(get))
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else:
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# scalar based property decorator
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def get(self):
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return getattr(self, attr_name).targets[0]
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def set(self, value):
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if getattr(self, attr_name) is None:
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setattr(self, attr_name, GenericAssoc(table.name))
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getattr(self, attr_name).targets = [value]
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setattr(cls, name, property(get, set))
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setattr(cls, 'member', property(lambda self: getattr(self.association, '_backref_%s' % self.association.type)))
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mapper(GenericAssoc, association_table, properties={
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'targets':relationship(cls, backref='association'),
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})
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return interface
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#######
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# addresses table
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addresses = Table("addresses", metadata,
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Column('id', Integer, primary_key=True),
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Column('assoc_id', None, ForeignKey('addresses_associations.assoc_id')),
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Column('street', String(100)),
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Column('city', String(50)),
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Column('country', String(50))
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)
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class Address(object):
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pass
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# create "addressable" association
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addressable = association(Address, addresses)
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mapper(Address, addresses)
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######
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# sample # 1, users
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users = Table("users", metadata,
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Column('id', Integer, primary_key=True),
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Column('name', String(50), nullable=False),
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Column('assoc_id', None, ForeignKey('addresses_associations.assoc_id'))
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)
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class User(object):
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pass
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mapper(User, users)
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# use the association
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addressable(User, 'addresses', uselist=True)
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######
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# sample # 2, orders
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orders = Table("orders", metadata,
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Column('id', Integer, primary_key=True),
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Column('description', String(50), nullable=False),
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Column('assoc_id', None, ForeignKey('addresses_associations.assoc_id'))
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)
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class Order(object):
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pass
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mapper(Order, orders)
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addressable(Order, 'address', uselist=False)
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######
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# use it !
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metadata.create_all()
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u1 = User()
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u1.name = 'bob'
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o1 = Order()
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o1.description = 'order 1'
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a1 = Address()
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u1.addresses.append(a1)
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a1.street = '123 anywhere street'
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a2 = Address()
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u1.addresses.append(a2)
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a2.street = '345 orchard ave'
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o1.address = Address()
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o1.address.street = '444 park ave.'
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sess = create_session()
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sess.add(u1)
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sess.add(o1)
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sess.flush()
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sess.expunge_all()
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# query objects, get their addresses
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bob = sess.query(User).filter_by(name='bob').one()
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assert [s.street for s in bob.addresses] == ['123 anywhere street', '345 orchard ave']
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order = sess.query(Order).filter_by(description='order 1').one()
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assert order.address.street == '444 park ave.'
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# query from Address to members
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for address in sess.query(Address).all():
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print "Street", address.street, "Member", address.member
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