Re: Reprise of Oracle decode functionality...now with nifty

Ack! Should at least pull the current version from the database:

This version also correctly checks the "default" return value for a
possible return of a wanted NULL value.  (The part just ahead of "return
$final_else;".

/*******************************************************************/

CREATE OR REPLACE FUNCTION pl.decode(selector text, clauses text)
   RETURNS text AS
$BODY$

use Safe;

my $vault;

# get / setup a safe "vault"  from / in %_SHARED to reduce function
start up time on a per session level

if ( exists( $_SHARED{pl_vault} ) && defined( $_SHARED{pl_vault} ) ){

    $vault = $_SHARED{pl_vault};
    #elog( NOTICE , "plperlu: Preloaded safety vault being used." );
}
else {
    # setup a safe vault using the same parameters as the SAFE_OK macro in
postgresql's
    #
http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plperl/plperl.c?rev=1.105

    $vault = Safe->new;
    $vault->permit_only( qw/ :default :base_math !:base_io time sort / );

    $_SHARED{pl_vault} = $vault;
    #elog( NOTICE , "plperlu: Setting up session safety vault.");
}

my $selector   = $_[0];
my @in_clauses = split( /,,/ , $_[1] );

#reject @in_clauses argument if it doesn't contain an odd number of
entries: ie -
#            ( '>10' , 'return#1' , 'final else' ) or ( '>10' ,
'return#1' , '<10' , 'return#2' , 'final else' )  is OK
#            ( '>10' , 'return#1' ) is not

die   "pl.decode(): invalid clause argument, the number of entries was
not odd.\n"
     unless ( scalar( @in_clauses ) % 2 );

my $final_else = pop @in_clauses;
my $retval     = undef;
my $have_match = undef;

ITERATIONS:
while ( @in_clauses ){
    my $match_clause = shift @in_clauses;
    my $then_clause  = shift @in_clauses;
    my $result       = $vault->reval( $selector . $match_clause );

    if ( my $error = $@ ){
        # safe reval error...clean up the error message then elog() and ignore
it, then move on and try the next set of match/result clauses...
        $error =~ s/ at line.+//;
        $error =~ s/trapped.+/deemed unsafe/;
        chomp $error;
        elog( NOTICE , "pl.decode(): potentially dangerous operation found, "
                              . $error
                              . ", skipping clause..."
                              );
        next ITERATIONS;
    }
    if ( $result ){ # we have the winner...set $retval and bail out...we
only grab the first true result...

        $retval     = $then_clause;
        $have_match = "yes";
        last ITERATIONS;
    }
    # no $result? oh well try the next set...
}

if ( defined( $have_match ) ){
         # last check to see if we've matched anything...
         # and if so return it...accounting for the case where
         # the wanted return is NULL...
    if ( $retval =~ m/^ (?: null || undef ) \( \) $ /ix ) {
        $retval=undef;
    }
    return $retval;
}

# if we get here we are returning the "default" result value
# also accounting for the case where the wanted return is NULL...
if ( $final_else =~ m/^ (?: null || undef ) \( \) $ /ix ) {
        $final_else=undef;
}

return $final_else;

$BODY$
   LANGUAGE 'plperlu' IMMUTABLE SECURITY DEFINER;
COMMENT ON FUNCTION pl.decode(selector text, clauses text) IS '
#############################################
##   decode( selector text , clauses text )
##                       plperlu rendition of Oracle''s decode()
function.  Takes 2 args:
##                       the item to check, and a double comma (,,)
separated string
##                       listing of items to match and items to return
if the match is successful.
##                       The last entry in the string is the final
"else" return value.  The match
##                       sections may include boolean operations.  USE
DOLLAR
##                       QUOTING to setup the test/result string, it
WILL save you much hair pulling.
##
##                       If you want a return item to be NULL for an
option, use one of the
##                       following (case INSENSITVE) return values:
##                             null()   or
##                             undef()
##
##   provides its own Safe.pm compartment for the reevalution of the
match clauses
##
#############################################
';