Re^2: How to use a json string with nested array and nested hash elements?

[Anonymous Monk]

Wow, I didn't know Dumper could be called that way.

print Dumper(json_to_perl($tstJSON));

$VAR1 = {
'cost' => '1029.32',
'more_info' => 'G1',
'strarray' => [
    {
    'refill_report' => {
        'pick_location' => [
             {
                'inv' => '-25',
                'pickid' => '72b921:3d1939'
              },
              {
                'inv' => '67',
                'pickid' => '6020a6:7f20e0'
              },
              {
                'inv' => '72',
                'pickid' => '5c0c8b:13a351'
              },
              {
                'inv' => '75',
                'pickid' => '72c941:3d1938'
              },
              {
                'inv' => '-23',
                'pickid' => '9020f6:7352d1'
              }
         ],
          vendorid' => '1358301537311',
          'date' => 'Thu Jan 16 13:35:32 +0800 2013'
      },
          'inventory_report' => {
             'current_value' => '126.30',
             'transactid' => '1358301537312',
             'date' => 'Thu Jan 17 13:35:37 +0800 2013',
             'refill' => '69.91'
          }
    }
  ],
'prime_name' => "\x{4ea4}at1",
'deviceid' => 'iPad',
'ntype' => '',
'supplierid' => '1358301'
};

[Anonymous Monk]

Well, as aitap mentioned above, @jsonarray = $decoded_json->{strarray} is wrong; it should be $jsonarray = $decoded_json->{strarray}. (It makes no sense to call ref() on an array either.)

Anyway, since $strarray is an array reference, you access its elements with $strarray->[$index], and if you need the whole array (in the foreach), you need to write @$strarray. (With hashes, the equivalents are $somevar->{$key} and %$somevar, respectively.)

Your structure is... well, let's tackle the strarray. It is an array of a single element, and that element contains a hash. And that is where you went wrong. I think you missed the arrays altogether. There's one under pick_location and the other one was under strarray. But let's try this in code:

# let's use an intermediate variable.
# it's a good idea when dealing with complex data structures
my $strarray = $decoded_json->{strarray};

# enumerate over the first array.
for my $str (@$strarray) {
    # now you have a hash with refill_report
    # and inventory_report in $str

    # let's access the pick_location inside the refill_report hash
    my $refill = $str->{refill_report};
    my $pick_aref = $refill->{pick_location};
    for my $pick (@$pick_aref) {
        # now we have one hashref in $pick
        print $pick->{pickid}, "\n";
    }

    # let's try sorting
    # $a is an element of @$pick_aref; so it is a hashref
    my @sorted = sort { $a->{inv} <=> $b->{inv} } @$pick_aref;
    print Dumper($_) for @sorted;
}

It's not a bad idea to postfix your intermediate variables with _href or _aref (like I did for one variable) just to remember whether you are dealing with a hash reference or an array reference.

I hope this helps. I spent quite a while pondering on how to access a complex data structure that a module spat out for me, but that was quite a while ago.

[Anonymous Monk]

Thanks for the code samples! It's exactly what I needed.

I'm looking at what aitap wrote and what you wrote and I see one difference:

aitap & 7Stud: my @jsonarray = @{$decoded_json->{strarray}};

Anonymous Monk: my $strarray = $decoded_json->{strarray};

I am surprised by the use of a $variable (string) instead of an @variable (array). I expected to need the same variable as aitap and 7Stud mentioned. I will need to restudy the variables and references, it's been nearly 6 years since I last wrote programs.

Thank all of you for the explanations and examples. You have been very helpful.

[Anonymous Monk]

They dereference the array copying it to a new variable. This gives easier syntax, but the array is copied which might have performance implications. (They are very slight since the array is only a single element in this case.) Mine should have perhaps been named $strarray_aref since it was still a reference.

All the variables I was using were references, hence a scalar $variable which get dereferenced with @{ } or %{ } or ->

One thing I forgot to mention that the outermost loop in my code sample is pretty useless since the array is only a single element. It could be replaced with my $str = $strarray->[0];