On Apr 19, 2012, at 6:23 AM, lars van gemerden wrote:
> I am trying to my my joined inheritance code clearer, for the dynamic
> generation of sa classes and tried to do something like this:
>
>
> class InheritMixin(object):
>
> @declared_attr
> def __tablename__(cls):
> return cls.__name__
> @declared_attr
> def id(cls):
> if cls.__name__ == 'Object':
> return Column(Integer, primary_key = True)
> else:
> print 'in id: ', cls.__name__, cls.__bases__[0].__name__
> return Column(Integer,
> ForeignKey(cls.__bases__[0].__name__ + '.id'), primary_key = True)
> @declared_attr
> def __mapper_args__(cls):
> if cls.__name__ == 'Object':
> return {'polymorphic_on': 'discriminator'}
> else:
> print 'in mapper_args: ', cls.__name__,
> cls.__bases__[0].__name__
> return {'polymorphic_identity': cls.__name__,
> 'inherit_condition': (cls.id ==
> cls.__bases__[0].id)}
>
> Object = type('Object', (Base, InheritMixin), clsdict)
>
> Where Object should be the (not necessarily direct) baseclass of all
> inheriting classes. However I get errors: "Mapper Mapper|person|person
> could not assemble any primary key columns for mapped table 'Join
> object on Object(65389120) and person(65428224)' " etc ..
im not sure of the cause of that error, can you attach a full test case which
illustrates this message being generated ?
>
> I noticed that the method __mapper_args__(cls) is always called before
> id(cls) (which is never called, probably due to the error.
the __mapper_args__(cls) method here directly calls upon .id, so if you see
.id() not being called it suggests some other form of .id is being used.
Is it possible that Base or something else has a conflicting "id" attribute?
>
> Also, is there a way to add the discriminator column to the mixin (if
> i just directly add it to the declaration, this gave another maybe
> related error)?
maybe, let's start with the general idea of the mixin you're going to send me
as a working script.
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