return json structure using perl - json

Question

i have the following sql statement inside a function..
my $sth = $dbh->prepare(qq[SELECT device_uuid,device_name FROM ].DB_SCHEMA().qq[.user_device WHERE user_id = ?]);
$sth->execute($user_id) || die $dbh->errstr;
the results are being fetched using the following statement
while(my $data = $sth->fetchrow_arrayref()) {
}
my question is how can i create and return a json structure containing objects for every row being fetched?something like this
{
object1:{
"device_uuid1":"id1",
"device_name1":"name1"
},
object2:{
"device_uuid2":"id2",
"device_name2":"name2"
},
object3:{
"device_uuid3":"id3",
"device_name3":"name3"
}
}
the total number of json objects will be equal to the number of rows returned by the sql statement.
i have managed to build the structure like this
$VAR1 = [{"device_name":"device1","device_id":"device_id1"},{"device_name":"device2","device_id":"device_id2"}]
how can i iterate through the array refs and get "device_name" and "device_id" values?

Answer 1

For your needs, this library should work well. What you need to do is have a scalar variable defined as below and push the element for each iteration in while loop
my $json = JSON->new->utf8->space_after->encode({})
while(my $data = $sth->fetchrow_arrayref()) {
#Push new element here in $json using incr_parse method
#or using $json_text = $json->encode($perl_scalar)
}
Hope this helps you.

Answer 2

finally what i did was to create an array ref and push the fetched rows which are being returned as hash refs
my #device = ();
while(my $data = $sth->fetchrow_hashref()) {
push(#device, $data);
}
last i convert the #device array ref to json and return the outcome
return encode_json(\#device);

Answer 3

The statement handle method fetchall_arrayref() can return an array reference where each element in the referenced array is a hash reference containing details of one row in the resultset. This seems to me to be exactly the data structure that you want. So you can just call that method and pass the returned data structure to a JSON encoding function.
# Passing a hash ref to fetchall_arrayref() tells it to
# return each row as a hash reference.
my $json = encode_json($sth->fetchall_arrayref({});

Answer 4

Your sample JSON is incorrect - JSON is actually quite nicely represented by perl data structures - [] denotes array, {} denotes key-value (very similar to hash).
I would rather strongly suggest though, that what you've asked for is probably not what you want - you've seemingly gone for globally unique keys, which ... isn't good style when they're nested.
Why? well, so you can do things like this:
print $my_data{$_}->{'name'} for keys %my_data;
Far better to go for something like:
#!/usr/bin/env perl
use strict;
use warnings;
use Data::Dumper;
use JSON;
my %my_data = (
object1 => {
uuid => "id1",
name => "name1"
},
object2 => {
uuid => "id2",
name => "name2"
},
object3 => {
uuid => "id3",
name => "name3"
},
);
print Dumper \%my_data;
print to_json ( \%my_data, { 'pretty' => 1 } )."\n";
Now, that does assume your 'object1' is a unique key - if it isn't, you can instead do something like this - an array of anonymous hashes (for bonus points, it preserves ordering)
my #my_data = (
{ object1 => {
uuid => "id1",
name => "name1"
}
},
{ object2 => {
uuid => "id2",
name => "name2"
}
},
{ object3 => {
uuid => "id3",
name => "name3"
}
},
);
Now, how to take your example and extend it? Easy peasy really - assemble what you want to add to your structure in your loop, and insert it into the structure:
while(my $data = $sth->fetchrow_arrayref()) {
my $objectname = $data -> [0]; #assuming it's this element!
my $uuid = $data -> [1];
my $name = $data -> [2];
my $new_hash = { uuid => $uuid, name => $name };
$mydata{$objectname} = $new_hash;
}