OK, this helps, so how do i do this if i do not know the name of the
attribute to be checked in advance(the "value" in
@validates("value") )?
On Apr 15, 6:52 pm, Michael Bayer <[email protected]> wrote:
> using type() is equivalent to using a class declaration. The end result is
> the same, as are the mechanics of what goes on both from a Python as well as
> a SQLAlchemy perspective. So this works:
>
> Positive = type("Positive", (Base,), dict(__tablename__ =
> "positives", value = Column(Integer)))
>
> @event.listens_for(Positive.value, "set")
> def checkvalue(target, value, oldvalue, initiator)
> assert value > 0
>
> and also, since type() is equivalent to a class declaration, you can still
> use @validates, if you pass the function into the class dictionary, so that
> it is part of the class before declarative sends it off to mapper():
>
> @validates("value")
> def checkvalue(self, name, value):
> assert value > 0
> return value
>
> Positive = type("Positive", (Base,), dict(__tablename__ =
> "positives", value = Column(Integer), checkvalue=checkvalue))
>
> On Apr 15, 2012, at 12:37 PM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > I don't know what "@validates hangs a marker of the method that
> > mapper() uses when it instruments the class" means. I guess my
> > question now becomes: How do I add the event.listens_for descriptor to
> > the class, since i do not have a class declaration in the traditional
> > sense?
>
> > On Apr 15, 4:29 pm, Michael Bayer <[email protected]> wrote:
> >> @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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