On Jul 15, 2012, at 10:03 AM, Karol Kuczmarski wrote:
>
> Right, but as I've said before, it still has to be done on per-subclass
> basis. I'm not sure how typical my use case,
> but it seems fairly reasonable that most of the time, the `type` attribute
> would simply refer to polymorphic_identity
> directly:
>
> @property
> def type(self):
> return self.__class__.__mapper_args__['polymorphic_identity']
>
> Ideally, one would expect some capability that allows to create "default
> attribute implementation" that can be inherited in subclasses
> when it doesn't have appropriate column (in the mapped table) that could be
> mapped into the attribute. I don't know how desirable
> such a feature would be, though, because cases when one declarative class
> inherits from other and BOTH have a table mapped
> to them seem to be uncommon. Maybe even the (Abstract)ConcreteBase
> hierarchies are the only practical application?...
>
> In any case, thanks again for quick and insightful response. At least now I
> know what's the state of this "feature" :)
I'd be uncomfortable just going forward with new behavior for the "type"
attribute here and no others. What if the the concrete base is non abstract,
and has a whole host of other columns on it not present on other tables ?
What about the case of more than one level of inheritance (there's always a
tiny group of people who insist on making things that complex, so we have to
oblige...)? There should probably be a path that is generic.
The solution to every class having a "type" attribute here can be done without
repetition. At the moment you'd need to name it something slightly different,
like "type_", as the name "type" is hardcoded into the AbstractConcreteBase
right now, but assuming that were configurable and the names could work out,
you only need say:
class MyBase(AbstractConcreteBase):
@property
def type_(self):
return self.__mapper__.polymorphic_identity
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