Re: Dynamic binding in plpgsql function

On Wed, Mar 2, 2011 at 8:34 AM, Dmitriy Igrishin <dmitigr(at)gmail(dot)com> wrote:
> 2011/3/2 Merlin Moncure <mmoncure(at)gmail(dot)com>
>> On Tue, Mar 1, 2011 at 5:17 PM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
>> wrote:
>> > Hello
>> >
>> > 2011/3/2 Pierre Racine <Pierre(dot)Racine(at)sbf(dot)ulaval(dot)ca>:
>> >> Hi,
>> >>
>> >> I would like to write a generic plpgsql function with a text parameter
>> >> being a callback function name so that my general function can call this
>> >> callback function. e.g.:
>> >>
>> >> CREATE OR REPLACE FUNCTION ST_MyCallbackFunction(y int)
>> >>    RETURNS int AS $$
>> >>    DECLARE
>> >>    BEGIN
>> >>        RETURN someCalculationBasedOnY;
>> >>    END;
>> >>    $$ LANGUAGE 'plpgsql';
>> >>
>> >> CREATE OR REPLACE FUNCTION ST_MyGeneralFunction(callback text)
>> >>    RETURNS SETOF geomval AS $$
>> >>    DECLARE
>> >>        x integer;
>> >>        y integer;
>> >>    BEGIN
>> >>        y := somecalculation;
>> >>        x := 'callback'(y);  --This is what I need
>> >
>> > EXECUTE 'SELECT ' || callback || '($1)' USING y INTO x;
>> >
>> > there are no other way than EXECUTE
>> >
>> > attention - there is a sql injection risk
>>
>> another way if you are willing to write some C is to wrap and expose
>> OidFunctionCall1 so it takes oid of function you want to call.
>
> As always, Merlin shows the uncommon thinking! :-)
> Respect!

Thank you, and I would like to be able to claim original invention of
this idea, however I cannot: it came from none other than Tom
Lane...http://postgresql.1045698.n5.nabble.com/improvise-callbacks-in-plpgsql-td2052928.html
(for whom nary a day goes by that I am not thankful for his tireless
efforts).

merlin