How do write a dispatch table for methods? - perl

Question

I'm trying to get rid of the if statements at the end of a subroutine I'm writing to handle SELECT queries:
sub select_query {
my ($params, $query, $return_type) = #_;
my $qh = $dbx->prepare($query);
my $param_count = 1;
foreach my $param (#$params) {
$qh->bind_param($param_count++, $param);
}
$qh->execute;
if ($return_type eq 'fetchrow_array') {
return $qh->fetchrow_array;
}
if ($return_type eq 'fetchall_arrayref') {
return $qh->fetchall_arrayref;
}
... AND SO ON ...
}
I'm familiar with the idea of a dispatch table to call different subroutines. What code could I use to efficiently call the various dbi methods on the $qh handle?

Answer 1

All you need is $qh->$return_type(...).
If you wish to validate, you can use a trivial lookup table.
my #valid_return_types = qw( fetchrow_array ... );
my %valid_return_types = map { $_ => 1 } #valid_return_types;
die "..." if !$valid_return_types{$return_type};

Answer 2

You will need to define the dispatch table after creating the statement handle.
use strict;
use warnings;
use DBI;
use Data::Dumper;
my $dbh = DBI->connect("DBI:mysql:mysql:localhost", 'user', 'password');
my $sth = $dbh->prepare("select * from user");
my $return_type = 'fetchall_arrayref';
my %dispatch = (fetchall_arrayref => sub {return $sth->fetchall_arrayref},
fetchrow_array => sub {return $sth->fetchrow_array});
$sth->execute;
print Dumper $dispatch{$return_type}->();
UPDATE:
Actually, let me make a correction. You can, if you wish, define the dispatch table prior creating the statement handle.
my %dispatch = (fetchall_arrayref => sub {return $_[0]->fetchall_arrayref},
fetchall_hashref => sub {return $_[0]->fetchall_hashref('User')},
fetchrow_array => sub {return $_[0]->fetchrow_array});
my $dbh = DBI->connect("DBI:mysql:mysql:localhost", 'root', 'password') or die;
my $sth = $dbh->prepare("select * from user");
foreach my $type (qw(fetchall_arrayref fetchall_hashref fetchrow_array)) {
$sth->execute;
print Dumper $dispatch{$type}->($sth);
}