On Feb 7, 2012, at 3:31 PM, Dave wrote:
> I've got a class Keyword that is many to many to itself through a
> mapped association table. The association table tracks which keyword
> is a parent of through the keywords ids (PK). Please see the pastebin.
>
> http://pastebin.com/774YmjKD
>
> I have been reading the <a href="http://docs.sqlalchemy.org/en/latest/
> orm/relationships.html#sqlalchemy.orm.relationship">many to many</a>
> and <a href="http://docs.sqlalchemy.org/en/latest/orm/extensions/
> associationproxy.html">association proxy</a> documentation but can't
> figure out how to get sqlalchemy to do what I want.
the association proxy can be given any attribute name to point towards. your
example gets a little murky when you're trying to mix the usage of
"secondary/viewonly" along with an association object, so below is a
simplification that produces a smooth interface between Keywords:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.associationproxy import association_proxy
Base= declarative_base()
class Keyword(Base):
__tablename__ = "keywords"
id = Column(Integer, primary_key=True, autoincrement=True)
parents = association_proxy('parent_relations', 'pkeyword', creator=lambda
p:Relation(p, None))
children = association_proxy('child_relations', 'ckeyword', creator=lambda
c:Relation(None, c))
class Relation(Base):
__tablename__ = "relations"
def __init__(self, p, c):
self.pkeyword = p
self.ckeyword = c
parent = Column(Integer, ForeignKey('keywords.id', ondelete="CASCADE"),
primary_key=True)
rcw = Column(Integer, ForeignKey('keywords.id', ondelete="CASCADE"),
primary_key=True)
pkeyword = relationship("Keyword",
primaryjoin="Relation.parent==Keyword.id",
backref=backref("child_relations",
collection_class=set))
ckeyword = relationship("Keyword", primaryjoin="Relation.rcw==Keyword.id",
backref=backref("parent_relations",
collection_class=set))
k1, k2, k3, k4 = Keyword(), Keyword(), Keyword(), Keyword()
k1.parents.update([k3, k4])
k2.children.update([k1, k3])
assert k1.parents == set([k2, k3, k4])
assert k2.parents == set([])
assert k3.parents == set([k2])
assert k4.children == set([k1])
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