Perl DBI:评估中的raiseerror
这个问题涉及池上的评论:Perl DBI:评估中的raiseerror,perl,exception-handling,eval,dbi,raiseerror,Perl,Exception Handling,Eval,Dbi,Raiseerror,这个问题涉及池上的评论: [...] But if you're going to put an eval around every statement, just use RaiseError => 0. [...] 在这方面 在这种情况下,如果我将RaiseError设置为0,我会得到什么 #!/usr/bin/env perl use warnings; use 5.10.1; use DBI; my $db = 'my_test_sqlite_db.sqlite'; open
[...] But if you're going to put an eval around every statement, just use RaiseError => 0. [...]
在这方面
在这种情况下,如果我将RaiseError
设置为0
,我会得到什么
#!/usr/bin/env perl
use warnings;
use 5.10.1;
use DBI;
my $db = 'my_test_sqlite_db.sqlite';
open my $fh, '>', $db or die $!;
close $fh or die $!;
my ( $dbh, $sth );
eval {
$dbh = DBI->connect( "DBI:SQLite:dbname=$db", "", "", {} );
};
if ( $@ ) { print $@ };
my $table = 'my_sqlite_table';
say "RaiseError = 1";
say "PrintError = 0";
$dbh->{RaiseError} = 1;
$dbh->{PrintError} = 0;
eval {
$sth = $dbh->prepare( "SELECT * FROM $table" );
$sth->execute();
};
if ( $@ ) { print "ERROR: $@" };
say "\nRaiseError = 0";
say "PrintError = 1";
$dbh->{RaiseError} = 0;
$dbh->{PrintError} = 1;
eval {
$sth = $dbh->prepare( "SELECT * FROM $table" );
$sth->execute();
};
if ( $@ ) { print "ERROR: $@" };
say "\nRaiseError = 0";
say "PrintError = 0";
$dbh->{RaiseError} = 0;
$dbh->{PrintError} = 0;
eval {
$sth = $dbh->prepare( "SELECT * FROM $table" );
$sth->execute();
};
if ( $@ ) { print "ERROR: $@" };
输出:
RaiseError = 1
PrintError = 0
ERROR: DBD::SQLite::db prepare failed: no such table: my_sqlite_table at ./perl2.pl line 23.
RaiseError = 0
PrintError = 1
DBD::SQLite::db prepare failed: no such table: my_sqlite_table at ./perl2.pl line 33.
ERROR: Can't call method "execute" on an undefined value at ./perl2.pl line 34.
RaiseError = 0
PrintError = 0
ERROR: Can't call method "execute" on an undefined value at ./perl2.pl line 44.
如果由于某些原因失败,大多数$dbh方法将:
- (如果
选项设置为0)返回RaiseError
undef
- (如果
选项设置为1),立即退出脚本(“die”),并将错误原因作为退出消息给出RaiseError
RaiseError
设置为0
):
在这个片段中(复制自您在问题中提到的@ikegami的答案),您循环了一些DB连接设置列表;如果某个连接为您提供了一个undef
,您只需转到另一个连接,并且不做任何错误处理
但是,通常情况下,当错误发生时,您需要做的不仅仅是“nexting”,而且您还有两个选择:或者使用如下内容检查每个与$dbh
相关的语句:
$sth = $dbh->prepare('some_params')
or process_db_error('In prepare');
...
$res = $sth->execute('another_set_of_params')
or process_db_error('In execute');
...
$res->doAnythingElse('something completely different')
or process_db_error('In something completely different');
(仅当其对应的“左部分”在布尔上下文中计算为false
时,才会执行as或
部分)
…或者将所有这些都包装到Perlish“try catch”块中:
if (!eval {
$sth = $dbh->prepare('some_params');
...
$res = $sth->execute('another_set_of_params');
...
$res->doSomethingElse('something completely different')
...
1 # No exception
}) {
process_db_error($@);
}
选择什么,取决于您:这是“返回语句中的错误”和异常之间的共同决定(除了要获取实际错误,您必须询问$dbh对象)
但底线是你不能只写这个:
$sth = $dbh->do_something('that_can_result_in_error');
$sth->do_something('else');
。。。如果您确实将RaiseError
设置为0
。在这种情况下,脚本不会消亡,$sth
将被分配一个undef
,您将得到一个“派生”错误(因为您不能在undef
上调用方法)
这正是您最初问题中代码的最后一部分所发生的情况。这是预期的行为-DBI返回undef(当异常被关闭时);Perl不知道如何处理这个未定义的值,因此死亡。问题是什么?
$sth = $dbh->do_something('that_can_result_in_error');
$sth->do_something('else');