How to specify an association relation using declarative base

Question

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

Answer 1

Actually column duedate is created, but you don't get it as some model attribute when querying your models. I you need to define intermediate model for intake_modules_table table and setup relation to it instead of Intake. Sure, the access to columns of relation will be a bit longer (module.infakes[0].duedate, module.infakes[0].infake.code). Also you can setup association proxy to access list of Infake objects the same way you do now.