Thank you, i got it working now. For future reference:
Before creating a sa class with something like:
type(typename, (Base,), classdict)
I first create the classdict in which I define columns, __tablename__,
etc, and validators (relationships I add later).
The validators i create(using a subclass of dict as classdict in the
type() call, and typedef being an object holding the definition to be
used to create a sa class/table) with:
def createValidator(self, typedef):
# get names of attributes to be validated:
names = [attr.name for attr in typedef.attributes \
if attr.validates()]
#create validator method from validating method in the
attr
#definition in typedef:
def validator(obj, name, value):
return typedef[name].validate(value)
#turn into sa "@validate" descriptor (i don't get the
#mechanics completely, but still):
validates(*names)(validator)
#add to classdict
self['validator'] = validator
Hope this helps someone, open to questions ...
Cheers, Lars
On Apr 15, 7:20 pm, Michael Bayer <[email protected]> wrote:
> If you can't establish the event at class declaration time, then the
> @event.listens_for/event.listen() paradigm
> (seehttp://docs.sqlalchemy.org/en/latest/core/event.htmlfor background) can
> be applied to the class-bound attribute (which here is "Positive.value") at
> any time. "Positive.value" is an attribute generated by the mapping which is
> a result of using the declarative base.
>
> On Apr 15, 2012, at 1:10 PM, lars van gemerden wrote:
>
>
>
>
>
>
>
> > 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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