JSON formatting in Perl - json

Question

I am trying to create a JSON object that lists maps associated to a particular user, but haven't ever worked with nested JSON objects. This is what I want:
{
"success":"list of users maps",
"maps":[
{
"id":"1",
"name":"Home to LE",
"date_created":"1366559121"
},
{
"id":"2",
"name":"Test 1",
"date_created":"1366735066"
}
]
}
with this perl code:
my $maps = [];
for (my $x = 0; $x < $sth->rows; $x++) {
my ($id, $name, $date) = $sth->fetchrow_array();
my $map = qq{{"id":"$id","name":"$name","date_created":"$date"}};
push $maps, $map;
}
my $j = JSON::XS->new->utf8;
my $output = $j->encode({
"success"=>"list of users maps",
"maps"=>$maps
});
But the output I am getting is:
{
"success":"list of users maps",
"maps":[
"{\"id\":\"1\",\"name\":\"Home to LE\",\"date_created\":\"1366559121\"}",
"{\"id\":\"2\",\"name\":\"Test 1\",\"date_created\":\"1366735066\"}"
]
}
So when I process it in my Javascript, the data.maps[x].id is undefined. I am pretty sure that the JSON being output is incorrectly formatted.
Can anyone help me fix it?

Answer 1

It's undefined because what you have at data.maps[x] is not an object, but a string. Since a string has no property called id, you're getting undefined. I'd probably do something like this (if I couldn't change the perl script):
var mapData = JSON.parse(data.maps[x]);
//do stuff with mapData.id
But the better thing to do, is to make sure that it doesn't encode it as a string, but as proper JSON.
This part in your perl script:
my $map = qq{{"id":"$id","name":"$name","date_created":"$date"}};
Is simply making a quoted string out of all that data. Instead, what you want is an actual perl hash that can be translated into a JSON map/associative-array. So try this:
my $map = {
"id" => "$id",
"name" => "$name",
"date_created" => "$date"
};
push $maps, $map;
This way you actually have a perl hash (instead of just a string) that will get translated into proper JSON.
As an example, I wrote some test code:
use strict;
use JSON::XS;
my $maps = [];
push $maps, { id => 1, blah => 2 };
push $maps, { id => 3, blah => 2 };
my $j = JSON::XS->new->utf8->pretty(1);
my $output = $j->encode({
success => "list of blah",
maps => $maps
});
print $output;
When you run this, you get:
{
"success" : "list of blah",
"maps" : [
{
"blah" : 2,
"id" : 1
},
{
"blah" : 2,
"id" : 3
}
]
}