@validates hangs a marker of the method that mapper() uses when it instruments
the class, so if the class is already mapped then that train has left the
station. Taking a cab instead, you can just add the attribute event directly:
@event.listens_for(Positive.value, "set")
def checkvalue(target, value, oldvalue, initiator)
assert value > 0
if you want to return a new, mutated value then add retval=True to
listens_for().
On Apr 15, 2012, at 8:22 AM, lars van gemerden wrote:
> Hi,
>
> I need a way to dynamically add a validates method to a already
> created sqla class.
>
> In a normal class declaration you can add a validator by:
>
> class Positive(Base):
> __tablename__ = "positives"
> value = Column(Integer)
>
> def checkvalue(self, name, value):
> assert value > 0
> return value
> validates("value")(checkvalue)
>
> However if you get the class dynamically:
>
> Positive = type("Positive", (Base,), dict(__tablename__ =
> "positives", value = Column(Integer)))
>
> I can't figure out how to add the validator, either in the type() call
> or afterwards.
>
> Cheers, Lars
>
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