Thread

1. C trigger problem

   Patrick Welche <prlw1@newn.cam.ac.uk> — 2005-09-17T13:41:45Z

   I am trying to write a C trigger. Essentially
   
       TriggerData *in = (TriggerData *) fcinfo->context;
       HeapTupleHeader tuple=in->tg_trigtuple->t_data;
       Datum datum;    
       datum = GetAttributeByName(tuple, "unit_id", &isnull);
   
   and that last line fails with
   
   ERROR:  cache lookup failed for type 4664
   
   I haven't seen anything similar in the documentation.. What is wrong / the
   correct way of extracting values from the old/new rows in a C trigger fn?
   
   Cheers,
   
   Patrick
   
   

2. Re: C trigger problem

   Tom Lane <tgl@sss.pgh.pa.us> — 2005-09-17T14:08:40Z

   Patrick Welche <prlw1@newn.cam.ac.uk> writes:
   > I am trying to write a C trigger. Essentially
   >     TriggerData *in = (TriggerData *) fcinfo->context;
   >     HeapTupleHeader tuple=in->tg_trigtuple->t_data;
   >     Datum datum;    
   >     datum = GetAttributeByName(tuple, "unit_id", &isnull);
   
   > and that last line fails with
   
   > ERROR:  cache lookup failed for type 4664
   
   GetAttributeByName doesn't work on raw tuples-on-disk, because they
   don't contain any type ID info.  Use heap_getattr or one of the related
   functions instead (perhaps in combination with SPI_fnumber if you don't
   want a hardwired column number).
   
   It strikes me that the current API for GetAttributeByName and
   GetAttributeByNum is kinda broken, in that they cannot support this sort
   of usage.  The pre-8.0 API was little better, because back then they
   wanted a TupleTableSlot which you don't have readily available either in
   a trigger function.  Thoughts anyone?  Should we just deprecate these
   functions and be done with it?
   
   			regards, tom lane