Trouble adding to hash in perl - perl

Question

I am reading a file replacing data and returning output to json. When I try to add a new item to the hash I get the following error. Not a HASH reference When I use ref() I am getting HASH as the type.
I have tried.
my $json_data = decode_json($template);
$json_data->{CommandCenters}{NewItem} = ["haha","moredata"];
Gives the not a hash reference error
The $json_data is below.
{
"Location":"Arkansas",
"CommandCenters": [
{
"secretary": "jill",
"janitor": "mike"
}
],
}
I am looking for the following output after I add the element.
{
"Location":"Arkansas",
"city": "little rock"
"CommandCenters": [
{
"secretary": "jill",
"janitor": "mike"
},
{
"NewItem":["whatever","more data"]
}
],
}
If I use $json_data->{CommandCenters}[0]{NewItem} = ['whatever','sure']; I do not get an error but I get unexpected results.
The data is added but in the incorrect slot.
"commandcenters":
[
"secretary":"jill",
"janitor": "mike",
"newitem":
[
"whatever","sure"
],
]

Answer 1

To add a new element to an array, use push. As we
're dealing with an array reference, we need to dereference it first.
push #{ $json_data->{CommandCenters} }, { NewItem => ["haha", "moredata"] };

Answer 2

When I try to add a new item to the hash I get the following error. Not a HASH reference When I use ref() I am getting HASH as the type.
Attention to detail is a vital skill for a successful programmer. And you're missing something subtle here.
When you use ref(), I assume you're passing it your $json_data variable. And that is, indeed, a hash reference. But the line that generates your Not a HASH reference is this line:
$json_data->{CommandCenters}{NewItem} = ["haha","moredata"];
And that's not just treating $json_data as a hash reference ($json_data->{...}) it's also treating $json_data->{CommandCenters} as a hash reference. And that's where your problem is. $json_data->{CommandCenters} is an array reference, not a hash reference. It's generated from the bit of your JSON that looks like this:
"CommandCenters": [
{
"secretary": "jill",
"janitor": "mike"
}
]
And those [ .. ] mark it as an array not a hash. You can't add a new key/value pair to an array; you need to push() new data to the end of the array. Something like:
push #{ $json_data->{CommandCenters} }, { NewItem => ["haha", "moredata"] };
That will leave you with this data structure:
$VAR1 = {
'CommandCenters' => [
{
'janitor' => 'mike',
'secretary' => 'jill'
},
{
'NewItem' => [
'haha',
'moredata'
]
}
],
'Location' => 'Arkansas'
};
And encode_json() will turn that into the JSON that you want.