Use of boolean returning functions in a project

Question

Hello all gurus,
in my project, we have a fairly important packaged functions that return boolean values. Working with these ones in pl/sql is very fine. But sometimes we need to reuse these functions in SQL, but no luck because bools are usable under pl/sql only and can't interact in any way in SQL statements. So the workaround should be to use these functions to return us some Y/N or 1/0 to emulate boolean behavior in SQL statements.
Here what i tested with not luck:
-- not work
select r.role, sys.diutil.bool_to_int(dbms_session.is_role_enabled(r.role)) as is_role_enabled
from   dba_roles r;
-- not work
select r.role
from   dba_roles r
where  sys.diutil.bool_to_int(dbms_session.is_role_enabled(r.role)) = 1;
-- not work
select t1.id,
       bool_to_char(my_bool_func(t1.x, t1.y, ...)) as is_something
from   t1;
-- not work
select t1.id,
       sys.diutil.bool_to_int(my_bool_func(t1.x, t1.y, ...)) as is_something
from   t1;The odd wrapping trick as a last resort solution is working....
-- Works! Seems the only way, but a lot of wrapping work...
create or replace function my_bool_func_wrap(p_x number, p_y number, ...) return varchar2 as
begin
   return bool_to_char(my_bool_func(p_x, p_y, ...));
end;
select t1.id,
       my_bool_func_wrap((t1.x, t1.y, ...)) as is_something
from   t1;I read a lot, but no elegant and working way.
Is there a more standard, elegant universal way to call bool functions from SQL?
Is creating a custom type visible and usable from both pl/sql and sql, if possible, a way to go?
Any other pointers?
For new development, is it good to make my boolean type returning functions using SQL compatible type like CHAR (Y/N) or NUMBER (1/0) ? It will make us less wrapping job, but more and less elegant bool handling code on the pl/sql side.
What is the goal to have bool only in pl/sql and not usable in SQL? It's kind of a feature incompatibility in the same product. Strange...
Thanks a lot
Bruno

Answer 1

brlav wrote:
Finally, I'll have to dump the BOOLEAN return type to all our boolean functions and return char instead. With this I will be able to call then from SQL.... From this perspective, BOOLEAN is useless.I would not say that. Let's assume that you implement boolean in SQL as a single byte character string containing either Y or N, enforce that with a constraint and also add a not-null constraint to it.
You simply define two PL functions (not usable from SQL) that deals with the conversion. You use the one function to change boolean to char before hitting the SQL engine, and the other to convert char to boolean when getting data from the SQL engine.
As I/O routines are modularised, it means that you need to deal with these conversions once only when writing and once only when reading (per module).
Simple example:
SQL> create or replace function to_bool( c varchar2 ) return boolean is
  2  begin                                                            
  3          return( c = 'Y' );                                       
  4  end;                                                             
  5  /                                                                
Function created.
SQL>
SQL> create or replace function bool_to_char( b boolean ) return varchar2 is
  2  begin
  3          if b then
  4                  return( 'Y' );
  5          else
  6                  return( 'N' );
  7          end if;
  8  end;
  9  /
Function created.
SQL>
SQL> declare
  2          i       integer;
  3          b       boolean;
  4          flag    all_tables.temporary%type;
  5          tab     all_tables%rowtype;
  6  begin
  7          flag := bool_to_char(true);  
  8          select count(*) into i from all_tables where temporary = flag;
  9
10          select t.* into tab from all_tables t where rownum = 1;
11          b := to_bool( tab.temporary );
12  end;
13  /
PL/SQL procedure successfully completed.
SQL>