$data = {
 'foo' => {
           'one' => '1',
           'two' => '2'
          }
};

##</code><code>##

$data = {
 'foo' => [{
            'one' => '1',
            'two' => '2'
           },
           {
            'one' => '1',
            'two' => '2'
           }]
};

##</code><code>##

if(exists $data->{'foo'}->{'one'}){
..code..
}

##</code><code>##

if(defined @{$data->{'foo'}}){
..code..
}