I have been trying to create an association relation between two tables, intake and module .  Each intake has a one-to-many relationship with the modules.
However there is a coursework assigned to each module, and each coursework has a duedate which is unique to each intake.  
I tried this but it didnt work:
intake_modules_table = Table('tg_intakemodules',metadata,
   Column('intake_id',Integer,ForeignKey('tg_intake.intake_id',
                onupdate="CASCADE",ondelete="CASCADE")),
   Column('module_id',Integer,ForeignKey('tg_module.module_id',
                onupdate ="CASCADE",ondelete="CASCADE")),
   Column('dueddate', Unicode(16))
)
class Intake(DeclarativeBase):
    __tablename__ = 'tg_intake'
    #{ Columns
    intake_id = Column(Integer, autoincrement=True, primary_key=True)
    code = Column(Unicode(16))
    commencement = Column(DateTime)
    completion = Column(DateTime)
    #{ Special methods
    def __repr__(self):
        return '"%s"' %self.code
    def __unicode__(self):
        return self.code
    #}
class Module(DeclarativeBase):
    __tablename__ ='tg_module'
    #{ Columns
    module_id = Column(Integer, autoincrement=True, primary_key=True)
    code = Column(Unicode(16))
    title = Column(Unicode(30))
    #{ relations
    intakes = relation('Intake', 
        secondary=intake_modules_table, backref='modules')
    #{ Special methods
    def __repr__(self):
        return '"%s"'%self.title
    def __unicode__(self):
        return '"%s"'%self.title
    #}
When I do this the column duedate specified in the intake_module_table is not created.
Please some help will be appreciated here.
thanks in advance