如何从MongoDB聚合中读取未定义对象的属性？(How to read property of undefined object from MongoDB aggregation?)

 您应该先将这些行添加到您的代码中： 
 
use strict;
use warnings;
 
 他们将抓住潜在的错别字。 例如， $inventaris是与$inventory不同的变量。 你真的有意要有两个变量吗？ 很难从你的代码中知道。 同样，你真的有一个名为$naam的变量吗？ 
 
 是的，可以从2个独立的子文件写入文件。 目前， $name是您的startNewOrder子版本地。 一种让你的其他子文件可见的方法是在你的代码开始时声明它，使它在你的代码文件中是全局的。 你可以将你的format移动到你write的相同的子文件write吗？ 
 
 在你的代码中，使用chomp而不是chop是更合适的。 
 
 最好使用exists来检查是否存在散列键，然后将它与undef返回的值进行比较。 
 
use strict;
use warnings;

my $name = makeUniqueFileName();

# Sample data
my %inventory = (
    c1 => [ 1 .. 3 ],
    c2 => [ 4 .. 6 ]
);

addToOrder();

sub addToOrder { 
    print "give productcode:\n"; 
    my $code = <STDIN>; 
    chomp $code; 
    print "Give amount:\n"; 
    my $amount = <STDIN>;
    chomp $amount;
    if (not exists $inventory{$code}) {
        print "This product does not exist\n"; 
    }
    # etc...
}
 
 我意识到我没有回答你所有的问题。 也许您可以一次专注于一个问题，并提供一个自包含的，可运行的示例，其中包含一小部分实际数据。 我经常通过将我的代码减少到一个仍然重现问题的最小示例来解决我自己的问题。 

You should start by adding these lines to your code:
 
use strict;
use warnings;
 
They will catch potential typos. For example, $inventaris is a different variable from $inventory. Did you really mean to have two variables? It is hard to tell from your code. Similarly, do you really have a variable named $naam?
 
Yes, it is possible to write to a file from 2 separate subs. Currently, $name is local to your startNewOrder sub. One way to make it visible to your other sub is to declare it at the start of your code, making it global to your code file. Can you move your format into the same sub as your write?
 
In your code, it is more appropriate to use chomp instead of chop.
 
It is better to check for the existence of a hash key using exists than to compare it against the value returned by undef.
 
use strict;
use warnings;

my $name = makeUniqueFileName();

# Sample data
my %inventory = (
    c1 => [ 1 .. 3 ],
    c2 => [ 4 .. 6 ]
);

addToOrder();

sub addToOrder { 
    print "give productcode:\n"; 
    my $code = <STDIN>; 
    chomp $code; 
    print "Give amount:\n"; 
    my $amount = <STDIN>;
    chomp $amount;
    if (not exists $inventory{$code}) {
        print "This product does not exist\n"; 
    }
    # etc...
}
 
I realize I did not answer all of your questions. Perhaps you could focus on one question at a time, and provide a self-contained, runnable example with a small sample of actual data. I often solve my own problems by reducing my code to a minimal example which still reproduces the problem.