html-template-users

[htmltmpl] (newbie) How to populate an array of hash references one by one?

[Ken C. <ke...@ke...>]

Hi All,

I'm playing with HTML::Template, and I've run into something that should
be easy, but I don't see how it can work.

The docs say to pass many elements for a loop, you do this:

$template->param( loopvar => [
                       { name=>"foo",value=>"baloney" },
                       { name=>"bar",value=>"tiple" },
                       { name=>"blah",value=>"mulroney" },
                  ],
                );

So, I'm using anonymous array and hash operators to make an anonymous
array of hash references. (page 246, "The anonymous array composer",
camel book).

That's great, but what if you don't know your content at programming
time?

{Just for context, I'm using perl 5.6.1, HTML::Template 2.6, with "use
strict"}.

Ideally, I want to add a line at a time to that array, and then pass
that whole array to the param.  So, I tried various things:

# attempt 1
my @test = ();
push @test { name=>"foo",value=>"blitz" };
# Gets "Global symbol "%test" requires explicit package name at ...[push
line]"   !?!?! there is no %test.

# attempt 2
my @test = ();
push @test \{ name=>"foo",value=>"blitz" };
# Gets "Backslash found where operator expected at ...[push line]"

# attempt 3
my @test = ();
push @test [ { name=>"foo",value=>"blitz" } ];
# Gets "Type of arg 1 to push must be array (not array slice) at
...[push line]"


[more stuff along the same lines that didn't work...]  *grrr*


Okay, says I, I'll work on something else and wait for the muse to
strike.  I decide I'll figure out how to pass an array into a param...

# attempt 4
my @test = [
	{ a=>"b",c=>"d" },
	{ e=>"f",g=>"h" },
];
$template->param(itemloop => \@test);
# Gets "HTML::Template->output() : fatal error in loop output :
HTML::Template->param() : Single reference arg to param() must be a
has-ref!  You gave me a ARRAY. at ..."

# attempt 5
my %test;
$test{"a"}="b";
$test{"c"}="d";
$test{"e"}="f";
$template->param(itemloop => \%test);
# Gets "HTML::Template::param() : attempt to set parameter 'itemloop'
with a scalar - parameter is not a TMPL_VAR! at ..."

# attempt 6
my %test;
$test{"a"}="b";
$test{"c"}="d";
$test{"e"}="f";
$template->param(itemloop => %test);
# Gets "You gave me an odd number of parameters to param()! at ..."


Ach.  So, no better luck.  Clearly there's some simple skullduggery I'm
missing here.  Can anyone enlighten me?

Pointers to documentation would be fine, though the HTML::Template page
and the perldoc for HTML::Template didn't help too much already.

-Ken

Re: [htmltmpl] (newbie) How to populate an array of hash references one by one?

[Timm M. <tm...@ag...>]

><>
># attempt 1
>my @test = ();
>push @test { name=>"foo",value=>"blitz" };
># Gets "Global symbol "%test" requires explicit package name at ...[push
>line]"   !?!?! there is no %test.

You forgot a comma, so Perl interpreted it as something like this:

push @test{'name','foo',value','blitz'};

Adding a comma after @test will make it work


># attempt 2
>my @test = ();
>push @test \{ name=>"foo",value=>"blitz" };
># Gets "Backslash found where operator expected at ...[push line]"

This would have made a reference to a hash reference (if you had the comma 
in), which wouldn't have worked anyway.

><>
># attempt 4
>my @test = [
>         { a=>"b",c=>"d" },
>         { e=>"f",g=>"h" },
>];
>$template->param(itemloop => \@test);
># Gets "HTML::Template->output() : fatal error in loop output :
>HTML::Template->param() : Single reference arg to param() must be a
>has-ref!  You gave me a ARRAY. at ..."

To Perl, you're creating an array, the first element being an arrayref, 
which contains hashrefs.  What you actually wanted to do is:

my @test = (
         { a=>"b",c=>"d" },
         { e=>"f",g=>"h" },
);

Note parens instead of square brackets.


># attempt 5
>my %test;
>$test{"a"}="b";
>$test{"c"}="d";
>$test{"e"}="f";
>$template->param(itemloop => \%test);
># Gets "HTML::Template::param() : attempt to set parameter 'itemloop'
>with a scalar - parameter is not a TMPL_VAR! at ..."

This one is interesting.  Looks like HTML::Template trys to use the hashref 
in its scalar representation (like HASH(0xffffffff)) and then errors out 
when your param isn't a loop.


># attempt 6
>my %test;
>$test{"a"}="b";
>$test{"c"}="d";
>$test{"e"}="f";
>$template->param(itemloop => %test);
># Gets "You gave me an odd number of parameters to param()! at ..."

To Perl, your params are being flatened like this:

$template->param(itemloop => a,
         b => 'c',
         d => 'e',
         f
);

That's because the param method takes a list with all the parameters being 
flattened into a hash.  Since you're putting 'itemloop => ' first, Perl 
sees that as the first element in the hash.  That's why you need to use 
references.

Please read perldsc.

<>

Re: [htmltmpl] (newbie) How to populate an array of hash references one by one?

[Jayson P. <JP...@je...>]

        Attempt #1-3 are missing a comma between your array and your list. 
 Solution, use a comma.

        Attempt #4 is assigning an array reference as the first element of 
an array and then you are using a reference to that array.  Solution, use 
() instead of [] in your assignment.

        Attempt #5 is a hashref not an array ref.  Solution, put all your 
hash elements into an array.
 
        Attempt #6 is a hash itself, not even an array.

        I'd recommend using #1 with a comma like so (push @test, { 
name=3D>"foo",value=3D>"blitz" };) and you should be working.

        --Jayson





Ken Corey <ke...@ke...>
Sent by: htm...@li...
11/24/03 02:55 PM
 
        To:     htm...@li...
        cc: 
        Subject:        [htmltmpl] (newbie) How to populate an array of 
hash references one by one=3F


Hi All,

I'm playing with HTML::Template, and I've run into something that should
be easy, but I don't see how it can work.

The docs say to pass many elements for a loop, you do this:

$template->param( loopvar =3D> [
                       { name=3D>"foo",value=3D>"baloney" },
                       { name=3D>"bar",value=3D>"tiple" },
                       { name=3D>"blah",value=3D>"mulroney" },
                  ],
                );

So, I'm using anonymous array and hash operators to make an anonymous
array of hash references. (page 246, "The anonymous array composer",
camel book).

That's great, but what if you don't know your content at programming
time=3F

{Just for context, I'm using perl 5.6.1, HTML::Template 2.6, with "use
strict"}.

Ideally, I want to add a line at a time to that array, and then pass
that whole array to the param.  So, I tried various things:

# attempt 1
my @test =3D ();
push @test { name=3D>"foo",value=3D>"blitz" };
# Gets "Global symbol "%test" requires explicit package name at ...[push
line]"   !=3F!=3F! there is no %test.

# attempt 2
my @test =3D ();
push @test \{ name=3D>"foo",value=3D>"blitz" };
# Gets "Backslash found where operator expected at ...[push line]"

# attempt 3
my @test =3D ();
push @test [ { name=3D>"foo",value=3D>"blitz" } ];
# Gets "Type of arg 1 to push must be array (not array slice) at
...[push line]"


[more stuff along the same lines that didn't work...]  *grrr*


Okay, says I, I'll work on something else and wait for the muse to
strike.  I decide I'll figure out how to pass an array into a param...

# attempt 4
my @test =3D [
                 { a=3D>"b",c=3D>"d" },
                 { e=3D>"f",g=3D>"h" },
];
$template->param(itemloop =3D> \@test);
# Gets "HTML::Template->output() : fatal error in loop output :
HTML::Template->param() : Single reference arg to param() must be a
has-ref!  You gave me a ARRAY. at ..."

# attempt 5
my %test;
$test{"a"}=3D"b";
$test{"c"}=3D"d";
$test{"e"}=3D"f";
$template->param(itemloop =3D> \%test);
# Gets "HTML::Template::param() : attempt to set parameter 'itemloop'
with a scalar - parameter is not a TMPL=5FVAR! at ..."

# attempt 6
my %test;
$test{"a"}=3D"b";
$test{"c"}=3D"d";
$test{"e"}=3D"f";
$template->param(itemloop =3D> %test);
# Gets "You gave me an odd number of parameters to param()! at ..."


Ach.  So, no better luck.  Clearly there's some simple skullduggery I'm
missing here.  Can anyone enlighten me=3F

Pointers to documentation would be fine, though the HTML::Template page
and the perldoc for HTML::Template didn't help too much already.

-Ken










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Re: [htmltmpl] (newbie) How to populate an array of hash references one by one?

[Puneet K. <pk...@ei...>]

Ken Corey wrote:
> Hi All,
> 
> I'm playing with HTML::Template, and I've run into something that should
> be easy, but I don't see how it can work.
> 
> The docs say to pass many elements for a loop, you do this:
> 
> $template->param( loopvar => [
>                        { name=>"foo",value=>"baloney" },
>                        { name=>"bar",value=>"tiple" },
>                        { name=>"blah",value=>"mulroney" },
>                   ],
>                 );
> 
> So, I'm using anonymous array and hash operators to make an anonymous
> array of hash references. (page 246, "The anonymous array composer",
> camel book).
> 
> That's great, but what if you don't know your content at programming
> time?

This comes up frequently. Maybe the explanation(s) should be added to 
the H::T docs (htdocs!)

Apologies if you already know some of the following.

A 2-d table (columns x rows) is a common, dareisay, the only 
representation of a database table. That is how you will also (in all 
likelihood) display it on your html page. So, imagine that each row is a 
hash where each key is the fieldname, and the value is the value of that 
field for that row. Now, if you string up a bunch of such hashes in a 
list, you get an array of hashes. Of course, since an array can store 
only scalara, it is actually an array of refs to hashes. And, since the 
$template->param is nothing but a hash itself, and since value of a key 
in a hash is also a scalar, a ref to our array of refs to hashes is applied.

So, you have

$template->param('result' => $arrayref);

where arrayref is a ref to our array of refs to hashes.

If you are using DBI (which is what you would typically, to grab the 
data from a table), things get extremely easy. The 
$sth->fetchall_arrayref({}) conveniently fetches a ref to an array of 
refs to hashes... cool.

so,

$template->param('result' => $sth->fetchall_arrayref({}));

works groovy.

You can construct this programmatically if you are reading sequentially 
from a file.

my @result;
while (<FILE>) {
   my %row;
   ..
   ..
   do something to split the row and stuff it into %row
   ..
   ..
   push(@result, \%row);
}
$template->param('result' => \@result);

The main problem is if you don't know the names of the fields you are 
pulling from a table (such as you would if you were to SELECT * FROM 
table). Since the fieldnames become the hash keynames, you would not be 
able to display them in your html page, because you wouldn't know what 
you pulled. To get around this, you simply treat each row as an array of 
hashes where each hash contains only one key called 'field' (or 
whatever), and its value is the value of that field. So you end up with 
an array of hashes where each hash is an array of hashes where each hash 
is a single field and its value. Cool.

Please always use strict and -w.

Hth.

Re: [htmltmpl] (newbie) How to populate an array of hash references one by one?

[Ken C. <ke...@ke...>]

On Mon, 2003-11-24 at 20:19, Puneet Kishor wrote:
> This comes up frequently. Maybe the explanation(s) should be added to 
> the H::T docs (htdocs!)

Might be a good idea!

> $template->param('result' => $sth->fetchall_arrayref({}));

Thanks for pointing this out, the '({})' to arrayref would have thrown
me for a loop...uh...no pun intended.

> You can construct this programmatically if you are reading sequentially 
> from a file.

Thanks, this info allowed me to get it working in less than 30 seconds.
Yay!  I /knew/ it was something simple.  

> Please always use strict and -w.

The first two lines of my cgi script are:

#!/usr/bin/perl -w
use strict;

When you say to "use -w", is that sufficient?  What about if it's being
run under mod_perl and Apache::Registry so that line isn't, as I
understand it, being invoked.  Does the perl still check to see if there
are invocation flags on the first line and respect them?

Hrm...

-Ken

Re: [htmltmpl] (newbie) How to populate an array of hash references one by one?

[Puneet K. <pk...@ei...>]

On Nov 25, 2003, at 1:18 AM, Ken Corey wrote:

> On Mon, 2003-11-24 at 20:19, Puneet Kishor wrote:
>> This comes up frequently. Maybe the explanation(s) should be added to
>> the H::T docs (htdocs!)
>
> Might be a good idea!

yeah... maybe Sam T might consider adding something like what I wrote 
up... something that directly ties using DBI with H::T, because 
inevitably someone will want to use MySQL or some such.


>
>> $template->param('result' => $sth->fetchall_arrayref({}));
>
> Thanks for pointing this out, the '({})' to arrayref would have thrown
> me for a loop...uh...no pun intended.
>
>> You can construct this programmatically if you are reading 
>> sequentially
>> from a file.
>
> Thanks, this info allowed me to get it working in less than 30 seconds.
> Yay!  I /knew/ it was something simple.
>
>> Please always use strict and -w.
>
> The first two lines of my cgi script are:
>
> #!/usr/bin/perl -w
> use strict;
>
> When you say to "use -w", is that sufficient?

well, no... I really meant what you already have

#/usr/bin/perl -w
use strict;

you can also "use diagnostics" or splain if you really want a chatty 
system.

>  What about if it's being
> run under mod_perl and Apache::Registry so that line isn't, as I
> understand it, being invoked.  Does the perl still check to see if 
> there
> are invocation flags on the first line and respect them?
>

dunno. I don't use mod_perl or A::R. I am cc-ing this to the list (as 
you should do also) because someone else would likely have the answer 
to this (and other questions).

Re: [htmltmpl] (newbie) How to populate an array of hash references one by one?

[Andrew B. <an...@br...>]

On 11/25/03 at 1:24 AM, pk...@ei... (Puneet Kishor) wrote:

> 
> On Nov 25, 2003, at 1:18 AM, Ken Corey wrote:
>
> So, I'm using anonymous array and hash operators to make an anonymous
> array of hash references. (page 246, "The anonymous array composer",
> camel book).
> 
> That's great, but what if you don't know your content at programming
> time?
> 
> > On Mon, 2003-11-24 at 20:19, Puneet Kishor wrote:
> >> This comes up frequently. Maybe the explanation(s) should be added
> >> to the H::T docs (htdocs!)
> >
> > Might be a good idea!
> 
> yeah... maybe Sam T might consider adding something like what I wrote 
> up... something that directly ties using DBI with H::T, because 
> inevitably someone will want to use MySQL or some such.
> 


Seems to me that it's a question of using Perl data structures and
references, not really an H::T question. The H::T documentation is
already far superior to many modules out there. You need to draw the
line somewhere.

Whatever.

Andrew

Re: [htmltmpl] (newbie) How to populate an array of hash references one by one?

[Timm M. <tm...@ag...>]

>><>
>>The first two lines of my cgi script are:
>>
>>#!/usr/bin/perl -w
>>use strict;
>>
>>When you say to "use -w", is that sufficient?
>
>well, no... I really meant what you already have
>
>#/usr/bin/perl -w
>use strict;
>
>you can also "use diagnostics" or splain if you really want a chatty system.
>
>>  What about if it's being
>>run under mod_perl and Apache::Registry so that line isn't, as I
>>understand it, being invoked.  Does the perl still check to see if there
>>are invocation flags on the first line and respect them?
>
>dunno. I don't use mod_perl or A::R. I am cc-ing this to the list (as you 
>should do also) because someone else would likely have the answer to this 
>(and other questions).

You can put a 'use warnings;' instead of using -w.  There are also places 
in the mod_perl config where you can modify what switches perl is invoked 
with.

'use warnings' has the advantage that it can be lexically scoped, so you 
can shut off warnings you know are harmless for a block.