On Wed, Aug 3, 2011 at 4:19 PM, James Robinson <jlrob...@socialserve.com> wrote: > Hackers, > > Python's getattr() allows for dynamic lookup of attributes on an object, as > in: > > inst = MyClass(x=12, y=24) > v = getattr(inst, 'x') > assert v == 12 > > Oftentimes in writing data validating trigger functions, it'd be real handy > to be able to do a similar thing in plpgsql against column values in a row > or record type, such as making use of a trigger argument for hint as what > column to consider in this table's case. Oh, to be able to do something like > (toy example known to be equivalent to a check): > > CREATE OR REPLACE FUNCTION must_be_positive() RETURNS TRIGGER AS > $$ > begin > if getattr(NEW, TG_ARGV[0]) <= 0 > then > raise exception(TG_ARGV[0] || ' must be positive'); > end if; > > -- after trigger > return null; > end; > $$ LANGUAGE PLPGSQL; > > > A function which takes a row + a text column name, and / or a peer function > taking row + index within row would really open up plpgsql's expressivity in > cases where you're writing mainly SQL stuff, not really wanting to go over > to plpythonu or whatnot (whose description of rows are as dicts). > > Is there something in the internals which inherently prevent this? Or am I > fool and it already exists? > > Not having to defer to EXECUTE would be attractive.
Aside from the other great solutions mentioned, you can run a record type through hstore and pull fields dynamically that way. The hstore method is a variant of the general 'coerce everything to text' strategy. Florian's approach is likely faster, but more verbose? merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
