Query data laravel - php

Question

I want to know how get this working in laravel:
I have two tables: "orders" and "delivery_boys".
When an order is created I want to get "id" in table "delivery_boys" that correspond to the "store_id" in the "order" table.
which looks like that in mysql
SELECT `id` FROM `delivery_boys` WHERE store_id = '3'
Thanks for your help.
I use this function:
protected $table = 'orders';
public function addNew($data)
{
$user = AppUser::find($data['user_id']);
if(isset($data['address']) && $data['address'] > 0)
{
$address = Address::find($data['address']);
}
else
{
$address = new Address;
}
$add = new Order;
$add->user_id = $data['user_id'];
$add->store_id = $this->getStore($data['cart_no']);
$add->d_boy = $add->?????; <---- here i want to add from "delivery_boys" table the "id" that correspond to the "store_id" added just above from the "order" table ---->
$add->name = $user->name;
$add->email = $user->email;
$add->phone = $user->phone;
$add->address = $address->address;
$add->lat = $address->lat;
$add->lng = $address->lng;
$add->address = $address->address;
$add->d_charges = $this->getTotal($data['cart_no'])['d_charges'];
$add->discount = $this->getTotal($data['cart_no'])['discount'];
$add->total = $this->getTotal($data['cart_no'])['total'];
$add->payment_method = $data['payment'];
$add->payment_id = isset($data['payment_id']) ? $data['payment_id'] : 0;
$add->type = isset($data['otype']) ? $data['otype'] : 1;
$add->notes = isset($data['notes']) ? $data['notes'] : null;
$add->save();

Answer 1

run this before $add = new Order;
$d_boy = DB::table('delivery_boys')
->select('id')
->where('store_id', $this->getStore($data['cart_no']))
->first();
and then add it where you need it:
$add->d_boy = $d_boy->id;

Answer 2

$id= DB::table('delivery_boys')->select('id')->where('store_id', '=', $this->getStore($data['cart_no']))->get();