How to define metaclass for a class that extends from sqlalchemy declarative base ?

Wed Jul 3 00:12:09 EDT 2013

I use: Python 2.6 and sqlalchemy 0.6.1
This is what I am trying to do:
	from sqlalchemy.types import (
	 Integer,
	 String,
	 Boolean
	)
	from sqlalchemy.ext.declarative import declarative_base
 Base = declarative_base()
	class SampleMeta(type):
 def __new__(cls, name, bases, attrs):
 attrs.update({ 'id': Column('Id', Integer, primary_key=True),
 'name': Column('Name', String),
 'description': Column('Description', String),
 'is_active': Column('IsActive', Boolean)
 })
 return super(SampleMeta, cls).__new__(cls, name, bases, attrs)
 class Sample(Base):
 __tablename__ = 'Sample'
 __table_args__ = {'useexisting': True}
 __metaclass__ = SampleMeta
 def __init__(self, id, name, description, is_active):
 self.id = id
 self.name = name
 self.description = description
 self.is_active = is_active
 def __repr__(self):
 return "<(%d, '%s', '%s', %r)>" % (self.id, self.name, self.description, self.isactive)
And the error I am getting is this:
 TypeError: Error when calling the metaclass bases
 metaclass conflict: the metaclass of a derived class must be a (non-strict) subclass of the metaclasses of all its bases
Now, if I do the same thing above by using
 class Sample(object)
instead of
 class Sample(Base)
it works absolutely fine.
I need to update the attributes of the class dynamically. So, I will be using dynamic attribute and column names. And I need the above piece code to work in order to be able to get there.
**Please help**