all Column objects have to be on the base class if you're using single
table inheritance. declarative joins the Table and class definitions
together, and the base class has to represent the Table completely.
On Dec 17, 2008, at 10:36 PM, Jeffrey wrote:
>
> below is ext.declarative.py's doc:
>
> class Person(Base):
> __tablename__ = 'people'
> id = Column(Integer, primary_key=True)
> discriminator = Column(String(50))
> __mapper_args__ = {'polymorphic_on': discriminator}
>
> class Engineer(Person):
> __tablename__ = 'engineers'
> __mapper_args__ = {'polymorphic_identity': 'engineer'}
> id = Column(Integer, ForeignKey('people.id'),
> primary_key=True)
> primary_language = Column(String(50))
>
> For single-table inheritance, the ``__tablename__`` and ``__table__``
> class
> variables are optional on a class when the class inherits from another
> mapped
> class.
>
>
> according it i think it should be like this:
>
> class Engineer(Person):
> __mapper_args__ = {'polymorphic_identity': 'engineer'}
> primary_language = Column(String(50))
>
> but :
> File "c:\python25\lib\site-packages\sqlalchemy-0.5.0rc1-py2.5.egg
> \sqlalchemy\s
> ql\expression.py", line 2636, in description
> return self.name.encode('ascii', 'backslashreplace')
> AttributeError: 'NoneType' object has no attribute 'encode'
>
>
> what should i do? thanks
>
> >
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