Custom functions in Laravel - php

Question

I use Maatwebsite/Laravel-Excel package to upload CSV to DB. Before entering data to DB i wanna do some additional checks with the database. Something like Project_id available in the Project table. Where do i write the required checking function. Is it a proper way to write it in the same controller. I have seen some people create folder In app\Example and write function file in it
UPDATE :
please let me know is this a proper way to do
https://www.youtube.com/watch?v=fS8q_sD1sZM
This the sample CSV format
This the controller function
public function uploadDealerCSV()
{
if(Input::hasFile('file')){
$path = Input::file('file')->getRealPath();
$data = Excel::load($path, function ($reader) {
$reader->ignoreEmpty();
})->get();
if(!empty($data) && $data->count()){
foreach ($data as $key => $value) {
$insert[] = [
'project_id' => $value->project_id,
'dealer_bl_code' => $value->bl_code,
'reporgroup' => 104,
'added_by' => 73,
'updated_at' => '2017-08-08 10:34:54',
];
}
if(!empty($insert)){
DB::table('cts_project_list')->insert($insert);
//dd('Insert Record successfully.');
}
}
}
return back();
}
public function testFunction(){
}