I have the following python classes.
class Instrument (object):
def __init__ (self, name):
self.name = name
class Equity (Instrument):
def __init__ (self, name, currency_id):
Instrument.__init__(self, name)
self.currency_id = currency_id
class Currency (Instrument):
pass
Pretty simple cut down example. Equity has a relationship with a
currency
Mapping is as follows
instruments = Table ('instruments', metadata,
Column ('id', Integer, primary_key=True),
Column ('type', String (10), nullable=False),
Column ('name', String(50), nullable=False, unique=True),
Column ('currency_id', Integer, ForeignKey ('instruments.id'))
)
instrument_mapper = mapper (Instrument, instruments,
polymorphic_on=instruments.c.type, polymorphic_identity='instrument')
equity_mapper = mapper (Equity,
inherits=instrument_mapper, polymorphic_identity='equity')
currency_mapper = mapper (Currency,
inherits=instrument_mapper, polymorphic_identity='currency',
properties={'equities': relationship
(Instrument, backref=backref('currency',
remote_side=[instruments.c.id]))}
)
One thing I'm not sure about. The currency mapper should have a
relationship with Currency and not with Instruments. ie. I want to
restrict the relationship to Currencies.
Is there a standard way of going around this?
Nick
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