Laravel Query Builder "select" strange behaviour - php

Question

I have a problem with the following code:
public function index() {
$qObj = \DB::table('customers as c')
->join('companies_has_customers as chc', 'chc.comhc_cus_id', '=', 'c.cus_id')
->join('cuscategory as cc', 'chc.comhc_cca_id', '=', 'cc.cca_id')
->join('transactions as t','t.trn_cus_id', '=','c.cus_id')
->select('t.trn_id');
$qObj->where('comhc_com_id', '=', $this->companyId);
$res = array(
'count' => $qObj->count(),
'items' => $qObj->get()
);
//print_r($this->showLastQuery());
return parent::prepareResponse($res, 200, 'customers');
}
And this piece of code produces following SQL query:
select * from `customers` as `c`
inner join `companies_has_customers` as `chc` on `chc`.`comhc_cus_id` = `c`.`cus_id`
inner join `cuscategory` as `cc` on `chc`.`comhc_cca_id` = `cc`.`cca_id`
inner join `transactions` as `t` on `t`.`trn_cus_id` = `c`.`cus_id`
where comhc_com_id` = 1
QUESTION:
Why QueryBuilder produce select *... instead of select t.trn_id... as is requested in above syntax?

Answer 1

Change the order:
$res = array(
'items' => $qObj->get(),
'count' => $qObj->count()
);
and it will work.
But better, instead of querying DB twice, do this:
$items = $qObj->get();
$res = array(
'items' => $items,
'count' => count($items)
);
The problem with your code is count() method behaviour - it resets the columns property (set with select), that's all.

Answer 2

Put it in $qObj->get(['t.trn_id']) like this:
$res = array(
'items' => $items = $qObj->get(['t.trn_id']),
'count' => count($items) // count the cached $items
);
Instead of select ( Remove select('t.trn_id')).