printing json from perl is incorrect - json

Question

Im trying to print out in json format info that I have gotten, I think if I show what I have that will better explain everything.
foreach ...{
printer($versions);
}
sub printer
{
foreach ...{
my $results = id_cards();
my $toJsonResult = JSON::to_json($results);
print $toJsonResult;
}
}
sub id_cards
{
my $returnData = [];
for($x=1;$y < $vehicle->{'ROWS'};$x++ )
{
my $data;
$data->{year} = $vehicle->{$x}->{'YEAR'}; #there is more $data->repetativeness but not important to get the point
push(#$returnData,$data);
$y++
}
return $returnData;
}
the json that is printed:
[{"year":"2004"},{"year":"2004"}][{"year":"2002"},{"year":"2000"},{"year":"1994"}][{"year":"2004"},{"year":"1955"}][{"year":"2004"},{"year":"1955"}]
This is very close to what I want but there is no separation of the json "objects"? (not sure what the term is) but it makes it not valid json. What can I do to put the years grouped accordingly but in valid json.

Answer 1

You are printing multiple JSON texts in a loop. Each time you go around the loop, you print a new JSON text.
You should build your data structure in the loop, and then convert the whole thing to JSON afterwards.
e.g.
sub printer {
my #data;
foreach ...{
push(#data, id_cards());
}
print JSON::to_json(\#data);
}

Answer 2

You already have the right idea in the id_cards sub:
sub some_function {
my $return_array = [];
foreach (...) {
push(#$return_array, $some_result);
}
return $return_array;
}
Do the same thing in printer:
sub printer {
my $return_array = [];
# for ...
return $return_array;
}
Then in the outermost foreach at the top of the file do the same:
my $results = [];
foreach (...) {
push(#$results,printer($versions));
}
print JSON.to_json($results);
Only print once, at the last minute. JSON expects a fully formed data structure. If you don't give it everything then you can't expect it to know how to format it properly.
Of course, at this point, the function printer doesn't print anything. So it is misnamed. I would change its name to card_collection or something.

Answer 3

You're effectively doing the following:
my $result = [ { year => 2002 }, { year => 2003 } ];
my $toJsonResult = JSON::to_json($results);
print $toJsonResult; # [{"year":"2002"},{"year":2003"}]
my $result = [ { year => 2004 }, { year => 2005 } ];
my $toJsonResult = JSON::to_json($results);
print $toJsonResult; # [{"year":"2004"},{"year":2005"}]
my $result = [ { year => 2006 }, { year => 2007 } ];
my $toJsonResult = JSON::to_json($results);
print $toJsonResult; # [{"year":"2006"},{"year":2007"}]
That creates a new JSON document for each result, and jams them all together on STDOUT.
You want to create one document that's an array of all your results, so you need to place your all your results in an array.
my #results
my $result = [ { year => 2002 }, { year => 2003 } ];
push $results, $result;
my $result = [ { year => 2004 }, { year => 2005 } ];
push $results, $result;
my $result = [ { year => 2006 }, { year => 2007 } ];
push $results, $result;
my $toJsonResult = JSON::to_json(\#results);
print $toJsonResult; # [[{"year":"2002"},{"year":"2003"}],
# [{"year":"2004"},{"year":"2005"}],
# [{"year":"2006"},{"year":"2007"}]]