Обсуждение: C trigger problem

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

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