plpgsql: Cast 'new' record for insert statement - postgresql

Question

I try to build a history inside a table. Part of the history function are the following table attributes:
id: uuid
historycounter: int8
Each time a dataset is added to the table its historycounter is set to zero.
Each time a dataset is update the historycounter should be increased by one.
A before insert or update or delete on <table> for each row should do all the work.
For the update part of the trigger function this looks as follows:
execute format('update %I.%I set historycounter = historycounter + 1 where id = $1', schema_name, tab_name) using old.id;
-- execute format('insert into %I.%I select $1', schema_name, tab_name) using new::text:xx;
execute format('insert into %I.%I values ($1)', schema_name, tab_name) using new.*::text;
return null;
Updating the historycounter works fine. But what ever I try, I did not find a way to do the conversion from UPDATE into INSERT. I like to build it on the most generic way possible. So knowing and adding each attribute of the dataset (table) is not a way.
As far as I know new and old are of the type record. Casting a record to row should do the trick, but HOW?
Any hints are welcome!

Answer 1

You need to unpack composite value inside INSERT statement. This is SQL feature (not plpgsql feature). So using star * in USING clause should not to work. NEW and OLD are not record variables. They are composite variables with known type.
create table foo(a int, b varchar, c int);
create table foo2( a int, b varchar, c int);
create or replace function foo_insert_trg()
returns trigger as $$
begin
execute 'insert into foo2 values($1.*)' using new;
return null;
end;
$$ language plpgsql;
insert into foo values(10, 'ahoj', 20);
INSERT 0 0
select * from foo2;
┌────┬──────┬────┐
│ a │ b │ c │
╞════╪══════╪════╡
│ 10 │ ahoj │ 20 │
└────┴──────┴────┘
(1 row)