On Sep 24, 2008, at 5:19 PM, Doug Farrell wrote:
> class PressRoutingPress(Base):
> '''This class defines the many-to-many join table between press
> and press_routing.
> '''
> __tablename__ = "press_routing_press"
> __table_args__ = {'autoload' : True}
>
> press_id = Column(Integer, ForeignKey('press.id'),
> primary_key=True)
> press_routing_id = Column(Integer, ForeignKey('press_routing.id'),
> primary_key=True)
>
> class PressRouting(Base):
> '''This class defines the press_routing table information.
> '''
> __tablename__ = "press_routing"
> __table_args__ = {'autoload' : True}
>
> class Press(Base):
> '''This class defines the press table information.
> '''
> __tablename__ = "press"
> __table_args__ = {'autoload' : True}
>
> # many to many Press<->PressRouting
> press_routing = relation('PressRouting',
> secondary=PressRoutingPress,
>
> primaryjoin=id==PressRoutingPress.press_id,
> foreign_keys=[PressRoutingPress.press_id],
>
> secondaryjoin=PressRouting.id==PressRoutingPress.press_routing_id,
>
> foreign_keys=[PressRoutingPress.press_routing_id],
> uselist=False)
> #backref=backref('press'))
> #viewonly=True)
>
> This all works till I try to instantiate an instance of a Press()
> object, then I get the following exception:
when you use the "secondary" argument on relation(), that should be a
plain Table object and should not be mapped (i.e. there should be no
separate class for it):
press_routing_press = Table("press_routing_press", Base.metadata,
Column("press_id", Integer, ForeignKey('press.id'), primary_key=True),
Column("press_routing_id", Integer,
ForeignKey('press_routing.id'),primary_key=True)
)
class Press(Base):
...
press_routing = relation("PressRouting",
secondary=press_routing_press)
no other arguments to relation() are needed.
If you do want PressRoutingPress to be mapped, you use the association
object pattern, which means you aren't using the "secondary" keyword.
The non-declarative version is here:
http://www.sqlalchemy.org/docs/05/mappers.html#advdatamapping_relation_patterns_association
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