Are single element lists allowed in perl? - ajax

Question

I'm trying to dynamically create a list of values from an AJAX request (using Catalyst), like this:
my #listofvalues = #{$params->{parameter_with_many_values}};
Then I loop through the list to make database insertions (one for each value). Since I need to loop through various lists like the one above, I need to access the index of the list. I am currently doing it like this:
foreach my $key (0 .. $#listofvalues){
$table_model->new({
field1 => $listofvalues[$key],
field2 => $x,
field3 => $another_listofvalues[$key]
field4 => $yet_another_listofvalues[$key]
});
}
This seems to work fine when two or more elements are received in the request. Whenever a single element is received, I get an error like
[error] Caught exception in pbitdb::Controller::Subjects->add "Can't use string ("1") as an ARRAY ref while "strict refs" in use at /home/lioneluranl/svn/pbitdb/pbitdb/script/../lib/pbitdb/Controller/Subjects.pm line 119."
Where, in this case, 1 is the value received and line 119 is the line where #listofvalues is being declared.
Now I've tried several to workaround this issue, but haven't found anything that works both ways (for a single or for various values). Any suggestions?

Answer 1

Yes, single element lists are OK in Perl, as are arrays and references to such arrays.
#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;
sub new {
print Dumper \#_;
}
my $table_model = 'main';
for my $values ( [ 'a' .. 'c' ],
[ 'd' ]
) {
my $params = { parameter_with_many_values => $values };
my #listofvalues = #{ $params->{parameter_with_many_values} };
my #another_listofvalues = map uc, #listofvalues;
for my $key (0 .. $#listofvalues) {
my $x = rand;
$table_model->new({
field1 => $listofvalues[$key],
field2 => $x,
field3 => $another_listofvalues[$key]
});
}
}
How do you populate $params->{parameter_with_many_values}?
Update
It seems Catalyst::Request should mention that their "safe" parameters should be handled as follows:
#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;
for my $params ( { param_with_many_values => 'a' },
{ param_with_many_values => [ 'a' .. 'e' ] },
{ something => 'else' }
) {
my $value_or_values = $params->{param_with_many_values};
my #list_of_values = ref $value_or_values ? #$value_or_values
: defined $value_or_values ? $value_or_values
: ();
print Dumper \#list_of_values;
}

Answer 2

First of all, you are asking about arrays (a type of variable), not lists (a vague term which can take on numerous definitions, none of which are pertinent here).
Yes, you can have an array with only one element.
$ perl -e'my #a = "ele"; CORE::say 0+#a; CORE::say for #a;'
1
ele
That's not the problem. The problem is that
#{$params->{parameter_with_many_values}}
expects
$params->{parameter_with_many_values}
to contain a reference to an array, but it contains 1 instead. It was probably set using
$params->{parameter_with_many_values} = #a; # Assigns number of elements
instead of
$params->{parameter_with_many_values} = \#a;