On Jul 7, 2011, at 3:29 PM, James Studdart wrote:
> Hi all,
> I've got a question regarding hybrid properties and how to use them with
> single table inheritance.
>
> I've got a class hierarchy like this (in semi-pseudo code):
>
> class MyBase(object):
> # This has the tablename declared attr, id as primary key, generic table
> args etc.
>
> class Person(MyBase, Base):
> children = relationship('Children')
>
> class SpecialPerson(Person):
> partner = relationship('Person')
>
> Okay, so what I want is for SpecialPerson to return both it's own plus it's
> partners children. But, if I add to list of children of a special person, it
> only adds to it's local children list. Does that make sense?
>
> This is what I've got now, I'm stabbing around in the dark a little bit, so
> I'm hoping for some guidance in the correct way to do this with SQL Alchemy.
What you have is fine, though it is only functional at the instance level, that
is:
p = Session.query(SpecialPerson).first()
print p.children
At the class level, the __add__() operator doesn't have any behavior for
relationship() and also cls.partner is again a relationship() which doesn't
have a _children attribute. That is, this wouldn't work:
print
Session.query(SpecialPerson).filter(SpecialPerson.chlidren.contains(some_person))
Assuming you don't need that (class level behavior), you don't really need
@hybrid_property either. You can just use Python's standard @property.
If you *did* want that, it would be a little tricky, probably would need a
custom comparator.
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