Question regarding triggers

I'm writing a trigger but running into problems. My problem is that I can not determine anyway to tell what fields are in the *new* record. Without knowing what fields are there I get runtime errors if that's not what is being updated example:

CREATE FUNCTION "public"."check_shipment" () RETURNS trigger AS'
begin
If new.shipment_type_id = 4 then
--do something
end if;
return new;
end;

in the above example everything works if shipment_type_id is being updated. If it is not I will receive a run-time error because shipment_type_id is not part of the record new.

Please help,
Dmitri

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