Sql in Model - Undefined variable: db

This is my symple model:

<?php namespace App\Models;

use CodeIgniter\Model;


class banner extends Model {

$query_ = "SELECT img_banner FROM tab_4 WHERE m = 12";

$query = $db->query($query_);

return $query->getResultArray();

}

?>

I receive this error: Undefined variable: db

Which is the correct way for resolve the issue?

https://codeigniter.com/user_guide/datab...cting.html

You have to define db , its in the doc

Inside the Model:

PHP Code:

$db = $this->db; 


Outside:

PHP Code:

$db = db_connect();