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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