Template, sorting an array with only one member

FloydATC has asked for the wisdom of the Perl Monks concerning the following question:

Given an array of hashes, I want to use Template Toolkit to loop through the array sorted by a hash key 'name':

my @array = (
  { name => 'foo', value => 1 },
  { name => 'bar', value => 2 },
  { name => 'baz', value => 3 }
);
[download]

[% FOREACH element IN array.sort('name') %]   
[% element.name %]
[% END %]
[download]

This works ok if @array has zero or more than 1 member.

However, if @array has exactly 1 member, the virtual method "sort()" will instead return the contents of that one hash in alphabetical order. Needless to say, this causes the output to be completely wrong since "element.name" will now render as a series of empty strings because they will be undefined.

Obviously, there is no need to sort an array with only one member, but in actual use I have no way of knowing in advance how many members there will be.

Does anyone know of a known fix/workaround for this problem? How can I tell Template that "array" is in fact an array?

Update:

I found a workaround that seems to do the trick:

[% PERL %]
my $copy;
@{$copy} = $stash->get('array');
if (ref($copy) eq 'ARRAY') {
  $stash->set('copy', sort { $a->{'name'} cmp $b->{'name'} } @{$copy})
+;
}
[% END %]
[% FOREACH element IN copy %]
[% element.name %]
[% END %]
[download]

-- FloydATC

Time flies when you don't know what you're doing

Comment on Template, sorting an array with only one member Select or Download Code

Replies are listed 'Best First'.
Re: Template, sorting an array with only one member by choroba (Cardinal) on Oct 20, 2014 at 14:05 UTC
I can't replicate the problem: `#!/usr/bin/perl use warnings; use strict; use Template; my @arr = ( { name => 'Foo', value => 1 }, # { name => 'Bar', value => 2 }, ); 'Template'->new ->process(\'TEST: [% FOREACH element IN arr.sort("name") %] [% ele +ment.name %][% END %]', { arr => \@arr });` [download] Output: `TEST: Foo` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l] [select]
Re^2: Template, sorting an array with only one member by FloydATC (Deacon) on Oct 20, 2014 at 17:24 UTC
I've put together a test script demonstrating how my data model works. Please tell me this fails for you, or I might go insane. Bonus points if you can tell me how to fix it. #!/usr/bin/perl use strict; use warnings; use Template; my $container = Container->new(); $container->add( Object->new( name => 'foo', value => 10, usefulness => 0 ) ); $container->add( Object->new( name => 'bar', value => 20, meaning => 42 ) ); my $vars = { 'container' => $container }; my $template = <<EOT; container=[% container %] all: [% FOREACH element IN container.all.sort('name') %] [% element %] name is [% element.name %] [% END %] one: [% FOREACH element IN container.one(10).sort('name') %] [% element %] name is [% element.name %] [% END %] EOT my $tt = Template->new(); $tt->process(\$template, $vars); package Object; sub new { my $class = shift; my $self = {@_}; return bless($self, $class); } package Container; sub new { my $class = shift; my $self = {@_}; return bless($self, $class); } sub add { my $self = shift; my $new = shift; push @{$self->{'objects'}}, $new; } sub all { my $self = shift; return @{$self->{'objects'}}; } sub one { my $self = shift; my $filter = shift; return grep { $_->{'value'} == $filter } @{$self->{'objects'}}; } [download] -- FloydATC Time flies when you don't know what you're doing	[reply] [d/l]
Re^3: Template, sorting an array with only one member by Mr. Muskrat (Canon) on Oct 20, 2014 at 18:10 UTC
Container's one method is returning a single Object object instead of an array reference with a single Object object inside. The fix is quite simple: `sub one { my $self = shift; my $filter = shift; return [ grep { $_->{'value'} == $filter } @{$self->{'objects'}} ]; }` [download] Output: container=Container=HASH(0x1cc2e10) all: Object=HASH(0x1cdf6b0) name is foo Object=HASH(0x1cdf788) name is bar one: Object=HASH(0x1cdf6b0) name is foo	[reply] [d/l]
Re^3: Template, sorting an array with only one member by ysth (Canon) on Oct 20, 2014 at 18:16 UTC
Have one/all return arrayrefs, not lists? `sub all { my $self = shift; return $self->{'objects'}; } sub one { my $self = shift; my $filter = shift; return [ grep { $_->{'value'} == $filter } @{$self->{'objects'}} ]; }` [download]	[reply] [d/l]
Re^4: Template, sorting an array with only one member by FloydATC (Deacon) on Oct 20, 2014 at 18:32 UTC
Re: Template, sorting an array with only one member by LanX (Saint) on Oct 20, 2014 at 10:26 UTC
Great DWIM bug. :) More a TT question, but what happens if you always append an empty hash to the array? Of course doing the sort logic in Perl should always fix this. Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :)}	[reply]
Re^2: Template, sorting an array with only one member by FloydATC (Deacon) on Oct 20, 2014 at 10:44 UTC
More a TT question, but what happens if you always append an empty hash to the array? This would solve the Template problem but it would also require that I check for empty hashes in every single place that array is used. I want to keep the workaround within the template if at all possible. I'll see if I can find a way to do that. -- FloydATC Time flies when you don't know what you're doing	[reply]
Re: Template, sorting an array with only one member (code not words) by Anonymous Monk on Oct 20, 2014 at 10:56 UTC
Code talks louder than words :) `$ cat sort-list.tt2 [% MACRO blocker BLOCK %] [% FOREACH element IN array.sort('name') %] [% element.name %] [%- END -%] [%- END -%] [%- SET array = [ { name => 'foo', value => 1 }, { name => 'bar', value => 2 }, { name => 'baz', value => 3 } ]; blocker %] [%- SET array = [ { name => 'bar', value => 2 }, ]; blocker %] $ tpage sort-list.tt2 bar baz foo bar` [download] My code says it works ... so what does your code say?	[reply] [d/l]
Re^2: Template, sorting an array with only one member (code not words) by FloydATC (Deacon) on Oct 20, 2014 at 11:07 UTC
I get the same result if I define the array within the template. If the array is served as a reference through Template::process() then it doesn't work as expected. -- FloydATC Time flies when you don't know what you're doing	[reply]
Re^3: Template, sorting an array with only one member (code not words) by Anonymous Monk on Oct 21, 2014 at 02:17 UTC
I get the same result if I define the array within the template. If the array is served as a reference through Template::process() then it doesn't work as expected. Thats just more words :) but I'm glad to see choroba got you to play ;) and you figured it out	[reply]
Re^2: Template, sorting an array with only one member by Anonymous Monk on Oct 20, 2014 at 11:05 UTC
You must be giving it a hash instead of an array ... don't know how you managed to write that :) `[% MACRO blocker BLOCK %] [% FOREACH element IN array.sort('name') %] [% element.name %] [%- END -%] [%- END -%] [%- SET array = [ { name => 'foo', value => 1 }, { name => 'bar', value => 2 }, { name => 'baz', value => 3 } ]; blocker; %] [%- SET array = [ { name => 'bar', value => 2 }, ]; blocker; %] [%- ## A HASH IS NOT AN ARRAY OF HASHES SET array = { name => 'bar', value => 2 }; blocker; %]` [download] yadayadayada `* bar * baz * foo * bar * *` [download]	[reply] [d/l] [select]


Pathologically Eclectic Rubbish Lister
	PerlMonks