mysqli Object Oriented Programming

Question

I'm trying to make my login homepage work. At the first I built my query with mysql but I always got the error "query is empty" so I decided to change over to mysqli. I'm now getting the error "Warning: mysqli_query() expects at least 2 parameters". how can I call the first parameter "$db" in my "mysqli_query($db, $string)" from the method "connect()" in the class "database2" to make it work? I tried with " $result = $this->cxn->query($query)" but then i got the error "Fatal error: Call to undefined method Database2::query()

<?php

class Login
{
    private $username;
    private $password;
    private $cxn;    // Database object.

    function __construct($username, $password)
    {
        // Set data
        $this->setData($username, $password);

        // connect to db
        $this->connectToDb();

        //get Data
        $this->getData();
    }

   private function setData($username, $password){

             $this->username = $username;
             $this->password = $password;

            }

    private function connectToDb(){

            include 'models/database2.php';
            $vars = "include/vars.php";
            $this->cxn = new Database2($vars);

            }

    private function getData(){

          $query ="SELECT 'username', 'password' FROM 'users' WHERE 'username' = '$this->username'
                                    AND 'password' = '$this->password'";

           $result = mysqli_query($query) or die(mysql_error());
           $num_row = mysqli_num_rows($result); 

                 if ($num_row>1) {
                    return TRUE;
                 }else{
                      throw new Exception("The query was not successful!");
                  }
              }

      function close(){
        $this->cxn->close_connect();
            }

}
?>

Database2 class:

<?php


class Database2{


    private $host;
    private $user;
    private $password;
    private $database;

    function __construct($filename){
        if(is_file($filename)){
            include $filename;
        }else{
            throw new Exception("Error Processing Request");
            }
        $this->host     = $host;
        $this->user     = $user;
        $this->password =$password;
        $this->database =$database;

        $this->connect();       
      }

         public function connect(){
                      // connect to the server.
                     $db = new mysqli($this->host, $this->user, $this->password);    
                       if ($db->connect_errno) {
                           die("We are sorry, you could not be connected to the server,
                            plaese check your connection setting!");
                       }else{
                           echo "You are connected to the database";
                       }
                   }


      public function close_connect(){
        mysql_close();

      }
}


?>

i appreciate any help

Answer 1

If you use procedural style, you have to set and use a "$db" variable in the database2 class. Set the variable in the connect function:

$this->db = new mysqli($this->host, $this->user, $this->password); 

And then, you can use the $db in the database2 object

$result = mysqli_query($this->cxn->db, $query);