On Tue, Aug 17, 2010 at 07:32:41PM -0700, Enrico wrote: > Micahael gave me this advice: > http://groups.google.com/group/sqlalchemy/browse_thread/thread/df6e451855d13a60/386232232434ff92?lnk=gst&q=enrico#386232232434ff92 > in which there are two backrefs and I think it's declarative whereas > yours is classical.
Hmmm, that's more of a general one-to-many relation with an
association object - it doesn't enfore one-to-one-ness or reflexivity.
There is something I don't understand in there though - the node and
adj_node properties mutually overwrite one-another with backrefs. How
does that work?
Here's what I want to be able to do:
n1 = Node("Node1")
n2 = Node("Node2")
n1.peer = n2
print n2.peer
>>> Node("Node1")
print n1.peer
>>> Node("Node2")
q = session.query(Node)
n1 = q.filter_by(peer=n2).one()
Usual backref patterns don't work because the backref would need to be
named the same thing as the forward reference. Hence why I went with
an association object.
But since the association object has a relation to both nodes, there
not an easy way to know that n1's peer is the OTHER entry in
n1.node. Hence why I added the property an synonym.
Ross
>
>
> On Aug 18, 4:59 am, Ross Vandegrift <r...@kallisti.us> wrote:
> > Hi everyone,
> >
> > Does anyone have a good setup for one-to-one relationships that are
> > always symmetric and provide a common property to access the paired
> > object? Ie, it's always the case that:
> > 1) (x,y) is in the relation iff (y,x) is in the relation.
> > 2) x.peer = y
> > 3) y.peer = x
> >
> > Here's the best thing I've come up with so far. It's not perfect -
> > for instance, there's no way to query by partner.
> >
> > class Person(object):
> > def _get_partner(self):
> > if self.marriage:
> > return self.marriage.get_partner_of(self)
> > else:
> > return None
> > partner = property(_get_partner)
> >
> > class Marriage(object):
> > def __init__(self, a, b):
> > self.partners = [a, b]
> > def get_partner_of(self, a):
> > x = list(self.partners)
> > x.remove(a)
> > return x[0]
> >
> > person_t = Table('person', metadata,
> > Column('id', Integer, primary_key=True),
> > Column('marriageid', Integer, ForeignKey('marriage.id')))
> > marriage_t = Table('marriage', metadata,
> > Column('id', Integer, primary_key=True))
> >
> > person_m = orm.mapper(Person, person_t)
> > marriage_m = orm.mapper(Marriage, marriage_t,
> > properties={'partners': orm.relation(Person,
> > backref="marriage")})
> >
> > Ross
> >
> > --
> > Ross Vandegrift
> > r...@kallisti.us
> >
> > "If the fight gets hot, the songs get hotter. If the going gets tough,
> > the songs get tougher."
> > --Woody Guthrie
> >
> > signature.asc
> > < 1KViewDownload
>
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--
Ross Vandegrift
r...@kallisti.us
"If the fight gets hot, the songs get hotter. If the going gets tough,
the songs get tougher."
--Woody Guthrie
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