Re: Dynamic binding in plpgsql function

[Dmitriy Igrishin <dmitigr@xxxxxxxxx>]

2011/3/2 Merlin Moncure <mmoncure@xxxxxxxxx>

On Tue, Mar 1, 2011 at 5:17 PM, Pavel Stehule <pavel.stehule@xxxxxxxxx> wrote:
> Hello
>
> 2011/3/2 Pierre Racine <Pierre.Racine@xxxxxxxxxxxxx>:
>> 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)
>> Â ÂRETURNS int AS $$
>> Â ÂDECLARE
>> Â ÂBEGIN
>> Â Â Â ÂRETURN someCalculationBasedOnY;
>> Â ÂEND;
>> Â Â$$ LANGUAGE 'plpgsql';
>>
>> CREATE OR REPLACE FUNCTION ST_MyGeneralFunction(callback text)
>> Â ÂRETURNS SETOF geomval AS $$
>> Â ÂDECLARE
>> Â Â Â Âx integer;
>> Â Â Â Ây integer;
>> Â ÂBEGIN
>> Â Â Â Ây := somecalculation;
>> Â Â Â Âx := 'callback'(y); Â--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!
Â

merlin

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// Dmitriy.