accessing parsed json data in perl - json

Question

I have the following json data in a string $json:
{
"results": [{
"geometry": {
"location": {
"lat": 37.4224764,
"lng": -122.0842499
},
},
}]
}
I use the following to decode my JSON data.
my $decoded_json = decode_json( $json );
And I'm attempting at retrieving the latitude here:
my $lat=$decoded_json->{results}->{geometry}{location}{lat};
And Here:
my $lat=$decoded_json->{results}->{geometry}->{location}->{lat};
I'd like to know how to retrieve the lat and lng from this decoded data.

Answer 1

There's an array in your JSON, but no array dereference in your code. In other words, you completely overlooked the [ ... ] in the JSON. You need to specify which of the results you want. In the example in question, there is only one, so you could use the following:
my $loc = $decoded_json->{results}[0]{geometry}{location};
my $lat = $loc->{lat};
my $lng = $loc->{lng};
Of course, the whole point of using an array of results is that the number of results might vary. You will probably need a loop.
for my $result (#{ $decoded_json->{results} }){
my $loc = $result->{geometry}{location};
my $lat = $loc->{lat};
my $lng = $loc->{lng};
...
}
About the arrows...
my $lat = $decoded_json->{results}[0]{geometry}{location}{lat};
is short for
my $lat = $decoded_json->{results}->[0]->{geometry}->{location}->{lat};
When the -> is between {...} or [...], and {...} or [...], it can be omitted.
That's why there's no difference between
$result->{geometry}{location}{lat};
$result->{geometry}{location}->{lat};
( $result->{geometry}{location} )->{lat}; # Can't be omitted here.
my $loc = $result->{geometry}{location};
my $lat = $loc->{lat}; # Can't be omitted here.

Answer 2

Given the name of the key, "results", it is natural to expect there might be times where you get more than one result. The following will give you the coordinates for all results returned:
for my $r (#{ $decoded_json->{results} }) {
my ($lat, $lng) = #{ $r->{geometry}{location} }{qw(lat lng)}
# do something with coordinates
}
With recent Perl versions, you can re-write that as:
for my $r ($decoded_json->{results}->#*) {
my ($lat, $lng) = $r->{geometry}{location}->#{qw(lat lng)};
# do something with coordinates
}
Once again, decode_json gives you a Perl data structure. The fact that the contents of that structure were constructed by parsing a JSON document are completely irrelevant to what you do with it.
Working example (Cpanel::JSON::XS chokes on your JSON):
#!/usr/bin/env perl
use utf8;
use strict;
use warnings;
use JSON::MaybeXS qw( decode_json );
my $json_string = <<EO_JSON;
{
"results": [{
"geometry": {
"location": {
"lat": 37.4224764,
"lng": -122.0842499
}
}
}]
}
EO_JSON
my $data = decode_json($json_string);
for my $r (#{ $data->{results} }) {
my ($lat, $lng) = #{ $r->{geometry}{location} }{qw(lat lng)};
print "($lat,$lng)\n";
}
for my $r ($data->{results}->#*) {
my ($lat, $lng) = $r->{geometry}{location}->#{qw(lat lng)};
print "($lat,$lng)\n";
}