> >> - Using polymorphic, joined-table inheritance ? Forget
> >> about polymorphic_union(), just join all the tables together
> >> using outerjoin(). In 0.4, even the select_table argument
> >> becomes optional.
> >
> > i am not sure if i got this right (a month already). A-B-C works,
> > yes. But just explain to stupid me how would to do it for this
> > simple tree: A, B(A), C(B), D(A). (or anything else having at
> > least 2 siblings subclasses). All nodes have instances.
>
> a.outerjoin(b).outerjoin(c).outerjoin(d, a.c.id==d.c.id) ?
and that would be which one, select_table for D? nooo..
but how would A look like?
a.outerjoin(b).outerjoin(c).outerjoin(d) ?
That is, outerjoin everything? order of outerjoining does not matter?
hmm (testing testing)
IMO this is the general rule:
* any class X that has subclasses, should have in mapper()
select_table = root.join(base1).join(base2)...
.join(X)
.outerjoin(subclass1).outerjoin(subclass2)....
where base* are the levels between X and the root, and subclass* are
all subclasses under X.
* any class X that is leaf (has no subclasses), needs no select_table.
see the variant of examples/polymorph.py attached.
ok, then i'll take polymorpic_union() off joined-table duty...
> > Also, in the docs, u still talk about polymorphical concrete
> > inheritance, while it does not really work. i mean, haveing some
> > engineer.id=2 and some other manager.id=2 would break it... there
> > would be 2 rows of id=2. Unless u know how to fix it.
>
> well technically i think thered be a "type" column on each table
> too which you might make as part of a composite primary key. that
> way PKs are unique within the union of all three tables. we should
> make that work and fix the doc for it, but also i think youre the
> only person to ever even attempt concrete inheritance too :)
aha, good ole polymunion() will have a new job ;-)
can this composite primary key be made just for the union?
and the mapper should somehow know about it...
==========
see, i dont really know what i (or some user) will need.
so far i have an assert to save users from concrete polymorphism ;-).
although some tests do work...
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"sqlalchemy" group.
To post to this group, send email to sqlalchemy@googlegroups.com
To unsubscribe from this group, send email to [EMAIL PROTECTED]
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~----------~----~----~----~------~----~------~--~---
polymorph.py
Description: application/python
