php - receive returned value by class in oop -

i have class :

<?php class connection {     public $db;      public function __construct() {      $this->db = new mysqli('localhost', 'root', '', '');      if($this->db->connect_errno > 0){         die('error ' . $this->db->connect_error);     }     $this->db->set_charset("utf8");     }  }  class masssave extends connection {     public $sql;     public function insert_all {     // works             if ( $sql = $this->db->query("insert $db_name ($str_db_value) values ($str_form_value_found) ")) {             return true;                 }             else {             return false;             }     }   } ?> 

in masssave class seted $sql public , want use class in pages , register page

$save = new masssave; if ( $save->sql = true ) {     echo 'ok'; }  else {     echo 'failed'; } 

but upper code not working , echo 'ok' query failed ,

i use if ( $save->sql == true ) code echo 'failed'

i newbie in oop , think php classes ok , think doing wrong way checking returned value

1. replace $sql = $this->db->query $this->sql = $this->db->query -- $sql - local variable. $this->sql - object property
2. call proper method after $save = new masssave; use $save->insert_all()
3. use comparison (but not assigment) $save->sql = true - assigment, $save->sql == true - comparison. assigment reutrns value of variable, $save->sql = true true.