Date: Mon, 12 Sep 2005 09:36:46 -0600
From: Michael Fuhr <mike@fuhr.org>
To: fabrizio picca <fabrizio.picca@gmail.com>
Cc: pgsql-interfaces@postgresql.org
Subject: Re: help needed on SPI_modifytuple.
Message-ID: <20050912153646.GA55025@winnie.fuhr.org>
References: <1532344d050912071740e7c5d9@mail.gmail.com>
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On Mon, Sep 12, 2005 at 04:17:33PM +0200, fabrizio picca wrote:
> I'm trying to sipmply modify a tuple before it will be inserted in the db.
> The problem is that when it try to insert the modified tuple with
> SPI_modifytuple all i get is a SPI_ERROR_ARGUMENT negative (-6) .
> Could someone help me? i'm reallygoing crazy.
> 
> What i did is just a fire-before C trigger that acts like this:

Is the trigger fired on INSERT, UPDATE, or both?

>         oldtuple =  trigdata->tg_trigtuple; 
> 	newtuple = trigdata->tg_newtuple; 
[...]
>         rettuple=SPI_modifytuple(rel,newtuple,1,&attnum,&new_value,&isnull);

I didn't look closely at the rest of the code, but if the trigger
is fired on INSERT then you should pass oldtuple; newtuple will be
NULL, causing SPI_modifytuple() to fail with SPI_ERROR_ARGUMENT.
Here's an extract from "Writing Trigger Functions in C" in the
"Triggers" chapter of the documentation:

tg_trigtuple

  A pointer to the row for which the trigger was fired.  This is
  the row being inserted, updated, or deleted.  If this trigger was
  fired for an INSERT or DELETE then this is what you should return
  from the function if you don't want to replace the row with a
  different one (in the case of INSERT) or skip the operation.

tg_newtuple

  A pointer to the new version of the row, if the trigger was fired
  for an UPDATE, and NULL if it is for an INSERT or a DELETE.  This
  is what you have to return from the function if the event is an
  UPDATE and you don't want to replace this row by a different one
  or skip the operation.

-- 
Michael Fuhr