Re: insert rule doesn't see id field - Mailing list pgsql-sql

On Thu, Jan 09, 2003 at 07:54:04PM -0000, dev@archonet.com wrote:

> Sounds similar to the plpgsql example at:
> 
> http://www.archonet.com/pgdocs/lock-field.html
> 
> which silently discards changes. It's trivial (apart from quoting issues)
> to write a trigger generator to customise the above in plpgsql (see the
> Cookbook on techdocs.postgresql.org for examples)

Ah - I wish I saw that earlier.  Thanks for pointer.  OTOH, I learned
something...

FWIW (probably just a good laugh):

#include "executor/spi.h"     /* this is what you need to work with SPI */
#include "commands/trigger.h" /* and triggers */
#include <ctype.h>            /* tolower () */
#include <stdlib.h>

extern Datum noupcols (PG_FUNCTION_ARGS);

/*
noupcols () -- revoke permission on column(s)

e.g.

CREATE FUNCTION noupcols ()    RETURNS opaque    AS '/usr/lib/postgresql/lib/noupcols.so'   LANGUAGE 'C';

CREATE TRIGGER person_noupcols   BEFORE UPDATE ON person   FOR EACH ROW   EXECUTE PROCEDURE noupcols( 'name_last', 'id'
);

Based on code from contrib/noup.c

The approach adopted here is to set the values of all of the columns
specified by noupcols to their old values.
*/

PG_FUNCTION_INFO_V1 (noupcols);

Datum
noupcols (PG_FUNCTION_ARGS)
{   TriggerData *trigdata = (TriggerData *) fcinfo->context;   Trigger     *trigger;           /* to get trigger name
*/  Relation    rel;                /* triggered relation */   char        **args;             /* arguments: column
names*/   int         ncols;              /* # of args specified in CREATE TRIGGER */   int         *colindices;
/*array of column indices to modify */   Datum       *oldcolvals;        /* old column values */   HeapTuple   oldtuple
=NULL;    /* tuple before being modified */   HeapTuple   newtuple = NULL;    /* new tuple after user-specified update
*/  HeapTuple   newnewtuple = NULL; /* tuple to return, after restoring newtuple's protected columns to their old
values*/   TupleDesc   tupdesc;            /* tuple description */   bool        isnull;             /* to know is some
columnNULL or not */   int         ret;   int         i;
 
   if (!CALLED_AS_TRIGGER (fcinfo))       elog(ERROR, "noup: not fired by trigger manager");
   if (TRIGGER_FIRED_FOR_STATEMENT (trigdata->tg_event))       elog (ERROR, "noup: can't process STATEMENT events");
   if (TRIGGER_FIRED_BY_INSERT (trigdata->tg_event))       elog (ERROR, "noup: can't process INSERT events");
   else if (TRIGGER_FIRED_BY_DELETE(trigdata->tg_event))       elog (ERROR, "noup: can't process DELETE events");
   oldtuple = trigdata->tg_trigtuple;   newtuple = trigdata->tg_newtuple;
   trigger = trigdata->tg_trigger;   rel = trigdata->tg_relation;
   tupdesc = rel->rd_att;
   ncols = trigger->tgnargs;   args = trigger->tgargs;
   colindices = (int *) malloc (ncols * sizeof (int));
   /* Connect to SPI manager */   if ((ret = SPI_connect()) < 0)       elog (ERROR, "noupcol: SPI_connect returned %d",
ret);
   /* Allocate space to place column values */   oldcolvals = (Datum*) palloc (ncols * sizeof (Datum));
   /* For each column ... */   for (i = 0; i < ncols; i++)   {       /* get index of column in tuple */
colindices[i]= SPI_fnumber (tupdesc, args[i]);
 
       /* Bad guys may give us un-existing column in CREATE TRIGGER */       if (colindices < 0)       {           elog
(ERROR,"noupcols: there is no attribute %s in relation %s",                 args[i],                 SPI_getrelname
(rel));          pfree (oldcolvals);           free (colindices);           SPI_finish ();           return
PointerGetDatum(NULL);       }
 
       /* Get previous value of column */       oldcolvals[i] = SPI_getbinval (oldtuple, tupdesc, colindices[i],
&isnull);  }
 
   /* Restore protected columns to their old values */   newnewtuple = SPI_modifytuple (rel, newtuple, ncols,
colindices,oldcolvals, NULL);
 
   pfree (oldcolvals);   free (colindices);   SPI_finish ();
   if (SPI_result == SPI_ERROR_ARGUMENT) {       elog (ERROR, "noupcols: bad argument to SPI_modifytuple\n");
returnPointerGetDatum (NULL);   }
 
   if (SPI_result == SPI_ERROR_NOATTRIBUTE) {       elog (ERROR, "noupcols: bad attribute value passed to
SPI_modifytuple\n");      return PointerGetDatum (NULL);   }
 
   return PointerGetDatum (newnewtuple);
}


-- 
Ron Peterson                          -o)
Network & Systems Manager             /\\
Mount Holyoke College                _\_v
http://www.mtholyoke.edu/~rpeterso   ----