Retrieving media upload in controller from array dynamically - json

Question

I am using Laravel 5.1 and I am using Illuminate\Http\Request instance for accessing sent file requests, but I can't seem to find the correct way to access the media element. I can access all other values in the object.
Here is the JSON data format I am using:
{"_method":"PUT",
"topic":"1 test",
"description":"1 test",
"media_description":"1 test",
"old_parts":
{"part-1":
{"sub_header":"test 2",
"text_field":"test 2 ",
"article_id":"18",
"media":{}},
"part-2":
{"sub_header":"test 3 ",
"text_field":"test 3",
"article_id":"18",
"media":{}}
},
"published":"1",
"media":{}
}
I access media in controller using two foreach loops, one loop is for database collection and other is for form content. I can use following method for accessing media elements.
if ($file = $request->file('media-' . $running_number)) {...}
But it decreases readability by huge amount as I should name the fields f.e. as media-1, media-2, ... and not access them using foreach loop like I do with everything else.
So is there a way to access file with foreach loop variable?
f.e. something like this
foreach($input['old_parts'] as $old_part) {
if ($old_part->hasFile('media')) { ... }
}
If I use the lines I typed the function returns a FatalThrowableError : Call to a member function hasFile() on array.
Or should I just use something like
$request->file('old_parts[part-'.$x.'][media]');
To access the file input and use custom variable to count the index? The problem is just that I can't figure out how to go inside multiple levels in JSON using file, as either old_parts['..']['..'] and old_parts['part-1']->media don't seem to return anything (return null).