Policy function not working (IN parameter not passed)

Hello alltogether,

I'm pretty much a newbie to Postgresql having spent the last 20 years

almost exclusively with Oracle. When trying to set up row level policy

in Postgres, got stuck with the issue mentioned at the end of this post.

The testcase provided is reduced as much as possible in order not to

distract from the issue.

Tests were performed in PG 12.2 and 12.3.

The test PG Cluster version 12.3 was installed from scratch.

Yet, same outcome as in 12.2

-- as postgres

create database db1;

create user db1_owner password 'db1_owner';

alter database db1 owner to db1_owner;

grant all privileges on database db1 to db1_owner;

-- as db1_owner in db1

create schema policy_test;

-- drop table policy_test.partners;

create table policy_test.partners(business_partner text);

insert into policy_test.partners ( business_partner) values ('125210000');

insert into policy_test.partners ( business_partner) values ('125210001');

-- alter table policy_test.partners disable row level security;

alter table policy_test.partners enable row level security;

-- drop function policy_test.get_partners(text);

create or replace function policy_test.get_partners(text)

  returns boolean as

$$

declare

  is_true   boolean := FALSE;

  the_count integer := 0;

begin

   select  count(*)

     into  the_count

     from  policy_test.partners a

    where  a.business_partner = '125210000'

      and  a.business_partner = $1;

   if the_count = 1 then

     is_true := TRUE;

   end if;

   return is_true;

end;

$$ language plpgsql;

-- drop policy test_partner_policy on policy_test.partners;

create policy test_partner_policy on policy_test.partners

  using (policy_test.get_partners(business_partner));

-- as postgres create pol_ex user;

create user pol_ex password 'pol_ex';

-- as db1_owner in db1

grant usage on schema policy_test to pol_ex;

grant select on policy_test.partners to pol_ex;

psql -U pol_ex -d db1

-- connect as pol_ex (ex here stands for "external" user)

select * from policy_test.partners;

Above select throws numerous lines shown underneath; sometimes in between the echoed SQL

error message max_stack_depth exceeded occurs. Beyond that no other error messages appear.

Whatever I tried the function does not accept / resolve the business_partner argument.

Is there a special way of indicating that this argument should be the tables' current row attribute?

Many examples on the Internet just pass the argument the way I tried.

Tried with prefixing scheme / table name to the argument, explict argument name instead of $ notation,

returning table of business_partners instead of boolean and so on, no avail.

Granting execute on the policy function to pol_ex did not help either.

I suspect a very basic issue due to my inexperience with Postgres.

If anyone of the seasoned Postgres Admins quickly can see what I did wrong, I'd be grateful for

a hint.

Thank you very much

Rainer Floegel

-- "Output" when running select * from policy_test.partners; (as pol_ex user)

SQL statement "select  count(*)

                          from  policy_test.partners a

    where  a.business_partner = '125210000'

      and  a.business_partner = $1"

PL/pgSQL function policy_test.get_partners(text) line 9 at SQL statement

SQL statement "select  count(*)

                          from  policy_test.partners a

    where  a.business_partner = '125210000'

      and  a.business_partner = $1"

PL/pgSQL function policy_test.get_partners(text) line 9 at SQL statement

and so on