I'm having trouble figuring out how to access the data on the 'one' side of a
'many-to-one' relationship.
If I have the following setup:
personTable = Table('person',
Column('person_id', Integer),
Column('name', String(20)),
Column('address', ForeignKey('address.address_id'),
)
addressTable = Table('address',
Column('address_id', Integer),
Column('street', String(20),
)
class Person(object):
pass
class Address(object):
pass
personMapper = mapper(Person, personTable)
addressMapper = mapper(Address, addressTable,
properties=dict(persons=relation(Person)))
Then I can do this:
session = create_session()
# Create one address
a = Address()
session.save(a)
a.street = "12 Maple Dr."
# Create two persons, each having the same address.
p1 = Person()
p2 = Person()
session.save(p1)
session.save(p2)
p1.name = "Joe Smith"
p1.address = a.address_id
p2.name = "Jane Smith"
p2.address = a.address_id
session.flush()
OK, now if I get a person:
p = session.query(Person).select(Person.c.name=="Jane Smith")[0]
I expect to be able to do something like:
street = p.address.street
But this just complains about 'None' not having an attribute 'street'.
I'm confused by this, because if I wanted to look up addresses and get the
persons living there, I'm able to do something like:
a = sesion.query(Address).select(Address.c.address_id==1)[0]
name = a.persons[0].name
This will lazily-evaluate the relationship, and get the appropriate Person
record for me.
Why is it easy to go in one direction, but not in the other. What am I missing?
Thanks.
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