connection with database with OOP mysqli extending class - php

Question

I know must coding part of mysql bt new at mysqli. I am not able to execute these insert query to the database. I have searched a lot but couldn't find simple suggestion, or may be i didn't understand.
Undefined variable: mysqli in C:\wamp\www\New folder\php\msqliconnect.php on line 32
Fatal error: Call to a member function mysqli_query() on a non-object in C:\wamp\www\New folder\php\msqliconnect.php on line 32
Any help is appreciated.
<?php
class connection
{
public $mysqli;
function connect()
{
$hostname = "localhost";
$username = "root";
$password = "";
$database = "demodatabase";
$mysqli = new mysqli($hostname, $username, $password, $database);
/* check connection */
if (mysqli_connect_errno())
{
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
return true;
}
}
class Index extends connection
{
function __construct()
{
parent::connect();
}
function insertdata($a, $b)
{
// echo $a. ' ' .$b;
// MySqli Insert Query
$status = 0;
$insert_row = $mysqli->mysqli_query("INSERT INTO tb_user (id, user, password, status) VALUES('','" . $a . "', '" . $b . "', '')");
if ($insert_row)
{
print 'saved';
}
else
{
die('Error : (' . $mysqli->errno . ') ' . $mysqli->error);
}
}
}
?>

Answer 1

In both of your connect() and insertdata() methods, you're using local variable $mysqli, not the instance variable public $mysqli;. You should use $this->mysqli instead of $mysqli in your instance methods. So your connect() and insertdata() methods would be like this:
function connect(){
$hostname = "localhost";
$username = "root";
$password = "";
$database = "demodatabase";
$this->mysqli = new mysqli($hostname, $username, $password, $database);
/* check connection */
if (mysqli_connect_errno()) {
printf("Connect failed: %s\n", mysqli_connect_error());
exit();
}
return true;
}
and
function insertdata($a, $b){
$insert_row = $this->mysqli->query("INSERT INTO tb_user (id, user, password, status) VALUES('','".$a."', '".$b."', '')");
if($insert_row){
print 'saved';
}else{
die('Error : ('. $this->mysqli->errno .') '. $this->mysqli->error);
}
}
Sidenote: Learn about prepared statement because right now your query is susceptible to SQL injection attack. Also see how you can prevent SQL injection in PHP.