can you do rollback in a trigger function?

I want to roll back deletion if there is a reference (FK) in another table.

Can I explicitly call a rollback inside a function?

CREATE OR REPLACE FUNCTION pre_del_prod_proc()

returns trigger as $$

begin

        if exists (select 1 from host_config where config_id = OLD.id) then

            rollback;

        end if;       

end;

$$ language plpqsql;

CREATE TRIGGER pre_del_prod_proc

before delete on prod_config

for each row execute procedure pre_del_prod_proc();

Thanks,

Quang.