Re: How to fire triggers just on "top" level DML

On Wednesday 19 January 2011 1:59:48 pm Kevin Grittner wrote:
> We've been running for about ten years on a framework which fires
> triggers similar to database triggers in a Java tier close to the
> database, and we're now trying to convert these to actual PostgreSQL
> database triggers.  Our biggest hitch at the moment is that we
> defined a class of triggers we called "top" triggers, which only
> fire from DML submitted by the application, not from DML issued by
> other triggers.
>
> One significant use of this is to block direct modification of
> summary data (either selected columns or entire tables) which are
> supposed to be trigger maintained.  It's not immediately obvious how
> to accomplish this within PostgreSQL, although I'm probably missing
> something.  We're not tied to any particular methodology -- a
> TG_DEPTH variable, if it existed, would do fine, for example.
>
> Any suggestions?
>
> -Kevin

The only thing I can think of off the top of my head is to you trigger arguments
and then use the below to test:

TG_ARGV[]

    Data type array of text; the arguments from the CREATE TRIGGER statement.
The index counts from 0. Invalid indexes (less than 0 or greater than or equal
to tg_nargs) result in a null value.

--
Adrian Klaver
adrian.klaver@gmail.com