如何在發生異常時訪問數據庫數據？

Question

我有下面的代碼：

my $savepoint = $c->db->txn_scope_guard; 
return $self->render('subnet/create', error => [ create => $@ ], 
    servers => $self->rows('Server')->lookup, 
) unless $subnet = eval{ $self->rows('Subnet')->create($subnet) }; 
$savepoint->commit; 

這裏rows是Mojolicious幫手，提供對數據的訪問。

sub model { 
    my($c, $table_name) = (shift,shift); 

    return $c->db->resultset($table_name); 
} 

而且->db也是幫手：

sub db { return $schema 
    //= DBIx::Class::Schema->connect($DB->{ DSN }, @$DB{ qw/ USER PASS/}, { 
     AutoCommit => 1, 
     RaiseError => 1, 
     quote_char => '"', 
    }) 
}); 

當我創建$subnet並且發生唯一約束（這裏有無論哪個約束出現，實際上任何異常的情況下），我得到了錯誤：

這是當我發現異常與eval{ ... }當前交易被中止，我不能做$self->rows('Server')->lookup

有沒有辦法在異常發生後訪問服務器數據？

Answer 1

我似乎找到了答案，因爲讀取錯誤消息更仔細：

... commands ignored until end of transaction block

所以我強迫事務塊結束時，異常發生：

$c->db->txn_rollback; 

代碼：

my $savepoint = $c->db->txn_scope_guard; 
unless($subnet = eval{ $self->rows('Subnet')->create($subnet) }) { 
    my $e = $@; # $@ may be changed before `create => $@` 
    undef $savepoint; # Or the same: $c->db->txn_rollback;  
    return $self->render('subnet/create', error => [ create => $e ], 
     servers => $self->rows('Server')->lookup, 
    ); 
} 
$savepoint->commit;