Building the varchar string to return from a pl sql function

Question

i'm new with pl/sql and i'm having trouble trying to build the string that i want to return from a function that is inside a package. it seems my problem stems from the fact that i'm trying to incorporate a variable (varchar2) into the string to be returned. below are two attempts that i've made which do not work:
function test_policy (p_schema_name IN varchar2, p_object_name IN varchar2) return varchar2 as
predicate_value varchar2(2000);
user_name varchar2(100);
begin
select first_name
into user_name
from employees
where first_name = SYS_CONTEXT('hr_app_context', 'username');
predicate_value := 'first_name = ' || user_name;
predicate_value := 'first_name = ' || '' || user_name || '';
return predicate_value;
end test_policy;
Can someone help me with the proper syntax to build my string for the return value? Thanks.

Answer 1

this function implements the code for a policy i've created. basically, the policy says that when i do a select on the employees table, i should only see a record whose first_name = sys_context('hr_app_context', 'username'). so, when i perform a simple select * from employees, i get an error which says policy predicate has error. i'm pretty sure the error is caused by how i'm building the return value for that function. if i hard code some return value like:
predicate_value := 'first_name = ''HR''' ;
the select statement above works fine, and i only see the record from employees where first_name = 'HR'