A colleague of mine submitted a question to StackOverflow (
http://stackoverflow.com/questions/5666732/sqlalchemy-self-referential-relationship-not-including-self
) which I've been struggling to answer (code given below for those who don't
want to visit the link).
Given, for example, a Film table and a Countries table, how can you add a
relationship to the Film mapper that will give you a list of countries that
have the same film, but which doesn't include the Film itself?
I tried:
primaryjoin=sqlalchemy.and_(
film_table.c.country_id==film_table.c.country_id,
film_table.c.id!=film_table.c.id)
but this doesn't work as it doesn't replace one of the `film_table.c.id`s with
a bindparam.
More generally, in a relationship, how do you force a column reference to be to
'self' and how does SQLalchemy decide which references are to 'self' and which
are to the objects it's going to get?
Thanks
Ed
Example code follows:
from sqlalchemy import Table, Column, Integer, String, MetaData, ForeignKey
from sqlalchemy.orm import mapper, relationship
metadata = MetaData()
country_table = Table('country', metadata,
Column('id', String, primary_key=True),
Column('name', String),
)
film_table = Table('film', metadata,
Column('id', Integer, primary_key=True),
Column('title', String),
Column('year', Integer),
Column('country_id', Integer, ForeignKey('country.id'))
)
class Country(object):
pass
class Film(object):
pass
mapper(Country, country_table)
mapper(Film, film_table,
properties={
'country':relationship(
Country,
backref='films'),
'same_country_films':relationship(
Film,
primaryjoin=film_table.c.country_id==\
film_table.c.country_id,
foreign_keys=[
film_table.c.country_id,
]
)
}
)
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