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 <mike...@zzzcomputing.com> 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 >> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "sqlalchemy" group. >>> To post to this group, send email to sqlalchemy@googlegroups.com. >>> To unsubscribe from this group, send email to >>> sqlalchemy+unsubscr...@googlegroups.com. >>> For more options, visit this group >>> athttp://groups.google.com/group/sqlalchemy?hl=en. > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalchemy@googlegroups.com. > To unsubscribe from this group, send email to > sqlalchemy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.