Perl DBI fetchall_hashref

Question

请考虑下表：

mysql> select * from vCountryStatus;
+-------------+------------+------+---------+--------+-----------------+
| CountryName | CountryISO | Code | Status  | Symbol | CurrencyName    |
+-------------+------------+------+---------+--------+-----------------+
| Brazil      | BR         |   55 | LIVE    | BRL    | Brazilian Real  |
| France      | FR         |   33 | offline | EUR    | Euro            |
| Philippines | PH         |   63 | LIVE    | PHP    | Philippino Peso |
+-------------+------------+------+---------+--------+-----------------+
3 rows in set (0.00 sec)

我正在尝试基于这个表构造一个哈希表。为此，我执行以下操作：

#!/usr/bin/perl

use DBI;
use Data::Dumper;

my $dbh = DBI->connect("dbi:mysql:database=db", "user", "password", {RaiseError => 1, AutoCommit => 0, FetchHashKeyName => "NAME_lc"}) || die "DB open error: $DBI::errstr";

my $sth = $dbh->prepare("select * from vCountryStatus");
$sth->execute;
my $hash = $sth->fetchall_hashref('countryiso');
print Dumper($hash);

下面是它生成的输出：

$VAR1 = {
          'PH' => {
                    'symbol' => 'PHP',
                    'status' => 'LIVE',
                    'countryname' => 'Philippines',
                    'countryiso' => 'PH',
                    'currencyname' => 'Philippino Peso',
                    'code' => '63'
                  },
          'BR' => {
                    'symbol' => 'BRL',
                    'status' => 'LIVE',
                    'countryname' => 'Brazil',
                    'countryiso' => 'BR',
                    'currencyname' => 'Brazilian Real',
                    'code' => '55'
                  },
          'FR' => {
                    'symbol' => 'EUR',
                    'status' => 'offline',
                    'countryname' => 'France',
                    'countryiso' => 'FR',
                    'currencyname' => 'Euro',
                    'code' => '33'
                  }
        };

问题是:为什么散列的键(countryiso)在散列的值中重复？

我更喜欢下面的输出：

$VAR1 = {
          'PH' => {
                    'symbol' => 'PHP',
                    'status' => 'LIVE',
                    'countryname' => 'Philippines',
                    'currencyname' => 'Philippino Peso',
                    'code' => '63'
                  },
          'BR' => {
                    'symbol' => 'BRL',
                    'status' => 'LIVE',
                    'countryname' => 'Brazil',
                    'currencyname' => 'Brazilian Real',
                    'code' => '55'
                  },
          'FR' => {
                    'symbol' => 'EUR',
                    'status' => 'offline',
                    'countryname' => 'France',
                    'currencyname' => 'Euro',
                    'code' => '33'
                  }
        };

是否可以使用fetchall_hashref DBI方法？或者我必须走传统的方式，遍历每一行并动态构建散列？

Answer 1

不能，这不能使用fetchall_hashref完成。但您可以遍历散列值并删除键：

delete $_->{countryiso} for values %$hash;

Answer 2

我也有同样的问题，但在fetchall_hashref上使用了多个键，所以我必须更深入地研究散列引用。不完全是火箭科学，但它是这样的：

(...)          
           my @keys=('key1','key2','key3');
           my $result_ref=$sth->fetchall_hashref(\@keys);

           remove_key_values($result_ref,\@keys);
(...)


sub remove_key_values {
    my ($href_values,$aref_keys) = (@_);

    foreach my $hk (keys %$href_values) {
        foreach my $ak (@$aref_keys) {
            if ($ak eq $hk) {
                delete $href_values->{$hk};
            }
        }
        if (exists $href_values->{$hk} and ref($href_values->{$hk}) eq 'HASH') {
                remove_key_values($href_values->{$hk},$aref_keys);
        }
    }
}