thanks, now I know what you mean by "the class will now have a table attached
to it". This behavior is a side effect of the issue raised in
http://www.sqlalchemy.org/trac/ticket/2656 (which also applies to 0.7), but
since __mapper_args__() is evaluated later, this turns it into more or less of
a regression, issue is fixed in r4ddeed7a3248.
On Apr 9, 2013, at 1:31 PM, Gerald Thibault <dieselmach...@gmail.com> wrote:
> Here is a test. It's possible the failure is because the provided example
> uses a mixin, while i am declaring directly on the base class.
>
> from sqlalchemy import *
> from sqlalchemy.ext.declarative import (declarative_base,
> declared_attr, has_inherited_table)
>
> Base = declarative_base()
>
> class Test(Base):
> __tablename__ = 'test'
> id = Column(Integer, primary_key=True)
> type = Column(String(20))
>
> @declared_attr
> def __mapper_args__(cls):
> if not has_inherited_table(cls):
> ret = {
> 'polymorphic_identity': 'default',
> 'polymorphic_on': cls.type,
> }
> else:
> ret = {'polymorphic_identity': cls.__name__}
> print '%s.__mapper_args__:' % cls
> print ret
> return ret
>
> class PolyTest(Test):
> __tablename__ = 'poly_test'
> id = Column(Integer, ForeignKey(Test.id), primary_key=True)
>
> Running this under 0.7.9 produces:
>
> <class '__main__.Test'>.__mapper_args__:
> {'polymorphic_identity': 'default', 'polymorphic_on': Column(None,
> String(length=20), table=None)}
> <class '__main__.Test'>.__mapper_args__:
> {'polymorphic_identity': 'default', 'polymorphic_on': Column(None,
> String(length=20), table=None)}
> <class '__main__.PolyTest'>.__mapper_args__:
> {'polymorphic_identity': 'PolyTest'}
>
> Running under 0.8.0 produces:
>
> <class '__main__.Test'>.__mapper_args__:
> {'polymorphic_identity': 'Test'}
> <class '__main__.PolyTest'>.__mapper_args__:
> {'polymorphic_identity': 'PolyTest'}
>
> in 7.9, the polymorphic_on was set correctly, in 8.0 the table already exists
> when the mapper_args are processed (because it's a lambda now), so
> has_inherited_table returns True. Is it intended behavior to have
> has_inherited_table return true when the only "inherited" table is that on
> the class itself? I am working around this by using my own
> has_inherited_table method, which first checks if the base is equal to the
> active class, and skipping it if they're the same. It seems this should be
> default behavior, unless i am misunderstanding what 'inherited' is
> representing here.
>
> Is there a way to accomplish what I'm trying to do without setting up my own
> has_inherited_table function?
>
>
> On Thursday, April 19, 2012 3:23:54 AM UTC-7, 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 ..
>
> I noticed that the method __mapper_args__(cls) is always called before
> id(cls) (which is never called, probably due to the error.
>
> Is there some way to fix this, while keeping the inheritance code in a
> mixin?
>
> 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)?
>
> Cheers, Lars
>
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