发生异常时如何访问数据库数据？

Question

我有下一个代码：

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;

这里的 rows 是 Mojolicious 助手，它提供对数据的访问。

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

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

而->db也是帮手：

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

当我创建$subnet 并发生唯一约束时（这里不管发生哪个约束，实际上是在任何异常的情况下）我得到了错误：

DBIx::Class::Storage::DBI::_dbh_execute(): DBI Exception: DBD::Pg::st execute failed: ERROR:  current transaction is aborted, commands ignored until end of transaction block [for Statement "SELECT "me"."id", "me"."hostname" FROM "servers" "me" ORDER BY hostname"] at ...

这是当我用eval{ ... } 捕获异常时，当前事务被中止，我不能做$self->rows( 'Server' )->lookup

有没有办法在异常发生后访问服务器数据？

Answer 1

似乎我找到了答案，因为更仔细地阅读错误消息：

...在事务块结束之前忽略命令

所以我在异常发生时强制结束事务块：

$c->db->txn_rollback;

代码：

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;