This if my first post so let me first just say spectacular job to
everyone involved. Coming from SQLObject, I was first turned off by the
the complexity but have grown to really like the flexibility (and the
great documentation)
I've created a mapper recently that looks to my untrained eye that it is
much more verbose than necessary. Here is the code, noting the
association_table mapper near the end:
###############################################
from sqlalchemy import *
db = create_engine('sqlite:///myeme.db')
metadata = BoundMetaData(db)
person_table = Table('person', metadata,
Column('person_id', Integer, primary_key=True),
Column('user_name', String(40))
)
class Person(object):
pass
mapper(Person, person_table)
association_table = Table('association', metadata,
Column('source_id', Integer,
ForeignKey("person.person_id"), primary_key=True),
Column('object_id', Integer,
ForeignKey("person.person_id"), primary_key=True),
Column('Comment', String(128))
)
class Association(object):
pass
mapper(Association, association_table, properties={
'source':relation(Person,
primaryjoin=association_table.c.source_id==person_table.c.person_id,
backref=backref("opinions",
primaryjoin=association_table.c.source_id==person_table.c.person_id,
cascade="all, delete-orphan")),
'object':relation(Person,
primaryjoin=association_table.c.object_id==person_table.c.person_id,
backref=backref("opinioned",
primaryjoin=association_table.c.object_id==person_table.c.person_id,
cascade="all, delete-orphan")),
})
#######################################################
I've had to create four primaryjoin statements yet all of the pertinent
information is contained in the table declaration. I understand the
initial ambiguity as I have two foreign relations to my "Person" table
and the mapper can't resolve which one is the "source" and which is the
"object". However shouldn't we be able to assign a simple
"OnColumn=THIS" (I am making up the name since I can't find it in the
docs) which means "we know it is ambiguous because two columns have the
same foreignkey, but we really mean THIS column". It isn't as much the
extra typing of writing a primaryjoin but that I want to make the table
definition more authoritative (ie I don't want to change the foreignkey
in the table then have to remember to change the mapper to match).
Does this exist? Would it make a good feature if it doesn't?
Also why does the backref need a primaryjoin? We've already resolved
the ambiguity with the forward reference so why can't it just follow it
backward to the proper column?
Thanks for any help, suggestions or thoughts anyone can provide. I am a
bit of a DB newbie so my apologies if I am missing something obvious.
Again great work to everyone involved.
-brian
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