Re: [Sqlalchemy-users] Problem with multiple one-to-many relations and backreferences

Michael Bayer Thu, 20 Jul 2006 09:36:43 -0700

yeah i can tell you exactly why this is this way.

when the backref is created, the 0.1 series just re-used the join conditions from the original relation (in the case of a primary and secondary join on a many-to-many, it reverses them). in 0.2 there were some problems with that....more complicated customized join conditions dont necessarily apply in reverse.

so for the moment you have to go more explicitly, if you have explicit join conditions:

properties = {

'payer' : relation(

Account,

primaryjoin=(\

accounts.c.payer_id==people.c.id),

backref=backref('payer_', primaryjoin=accounts.c.payer_id==people.c.id)),

'reciever' : relation(

Account,

primaryjoin=(\

accounts.c.reciever_id==people.c.id),

backref=backref('reciever_', primaryjoin=accounts.c.reciever_id==people.c.id))}

also the "foreignkey" parameter is usually not needed unless youre doing a self-referential mapper.

On Jul 20, 2006, at 11:14 AM, Vasily Sulatskov wrote:

from sqlalchemy import *

class SqlStrMixing( object ):

def __init__(self, **kwargs):

for key, value in kwargs.iteritems():

setattr(self, key, value)

def __str__( self ):

s = [ self.__class__.__name__ + ': ' ]

for c in self.c:

s.append( u'%s=%s ' % ( c.key, getattr(self, c.key) ) )

result = ''.join(s).encode( 'cp866' )

return result

engine_uri = 'sqlite:///'

metadata = BoundMetaData(engine_uri, convert_unicode=True)

people = Table('people', metadata,

Column('id', Integer,

primary_key=True),

Column('name', Unicode(100)))

accounts = Table('accounts', metadata,

Column('id', Integer,

primary_key=True),

Column('name', Unicode(100)),

Column('payer_id', Integer,

ForeignKey(people.c.id), index=True, default=None),

Column('reciever_id', Integer,

ForeignKey(people.c.id), index=True, default=None))

metadata.create_all()

class Person(SqlStrMixing):

pass

class Account(SqlStrMixing):

pass

mapper(Account, accounts)

# I use underscore to avoid confusion

properties = {

'payer' : relation(

Account,

primaryjoin=(\

accounts.c.payer_id==people.c.id),

foreignkey=accounts.c.payer_id,

backref='payer_'),

'reciever' : relation(

Account,

primaryjoin=(\

accounts.c.reciever_id==people.c.id),

foreignkey=accounts.c.reciever_id,

backref='reciever_')}

counteragent_mapper = mapper(Person,

people,

properties=properties)

session = create_session(echo_uow=True)

jack = Person(name='Jack')

john = Person(name='John')

acc = Account(name='123')

acc.payer_ = jack

session.save(jack)

session.save(john)

session.save(acc)

session.flush()

session.close()

session = create_session()

query = session.query(Account)

for a in query.select():

print a

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Re: [Sqlalchemy-users] Problem with multiple one-to-many relations and backreferences

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