PHP - Call to a member function query() on null - Error [duplicate] - php

Question

This question already has answers here:
Fatal error: Call to a member function query() on null
(2 answers)
Closed 5 years ago.
I have the following code in php for connecting to my database:
<?php
class MY_SQL{
private $username;
private $password;
private $conn;
public function __construct($SERVERNAME){
$this->username = "username";
$this->password = "password";
if($SERVERNAME == "data_"){
$server = "Servername";
}
else {
$server = $SERVERNAME;
}
// Create connection
$conn = new mysqli($server, $this->username, $this->password);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
}
public function SQLCommand($cmd) {
if ( $this->conn->query($cmd) === TRUE ) {
echo "New record created successfully";
} else {
echo "Error: " . $cmd . "<br>" . $conn->error;
}
}
}
$sql = "INSERT INTO _test(test1, test2) VALUES ('hello','hi');";
$database = new MY_SQL("Servername");
$database->SQLCommand($sql);
?>
I get the following error:
Fatal error: Call to a member function query() on null
What is going wrong?

Answer 1

$this->conn = $conn; in __construct()

Answer 2

I would suggest you to improve your class with this example (taken from https://github.com/opencart/opencart/blob/master/upload/system/library/db/mysqli.php)
final class My_SQLi
{
private $connection;
public function __construct($hostname, $username, $password, $database, $port = '3306')
{
$this->connection = new \mysqli($hostname, $username, $password, $database, $port);
if ($this->connection->connect_error) {
throw new \Exception('Error: ' . $this->connection->error . '<br />Error No: ' . $this->connection->errno);
}
$this->connection->set_charset("utf8");
$this->connection->query("SET SQL_MODE = ''");
}
public function query($sql)
{
$query = $this->connection->query($sql);
if (!$this->connection->errno) {
if ($query instanceof \mysqli_result) {
$data = array();
while ($row = $query->fetch_assoc()) {
$data[] = $row;
}
$result = new \stdClass();
$result->num_rows = $query->num_rows;
$result->row = isset($data[0]) ? $data[0] : array();
$result->rows = $data;
$query->close();
return $result;
} else {
return true;
}
} else {
throw new \Exception('Error: ' . $this->connection->error . '<br />Error No: ' . $this->connection->errno . '<br />' . $sql);
}
}
public function escape($value)
{
return $this->connection->real_escape_string($value);
}
public function countAffected()
{
return $this->connection->affected_rows;
}
public function getLastId()
{
return $this->connection->insert_id;
}
public function isConnected()
{
return $this->connection->ping();
}
public function __destruct()
{
$this->connection->close();
}
}
$sql = "INSERT INTO _test(test1, test2) VALUES ('hello','hi');";
$mysql = new My_SQLi('host', 'user', 'password', 'db');
$result = $mysql->query($sql);