how to change mysql_connect() to PDO - php

Question

This is my db connect class which is working with php5.3 but it not working after i updated the php5.4 and show error that it's expired.
class DB {
function DB() {
$this->host = "localhost";
$this->db = "dbtest";
$this->user = "root" ;
$this->pass = "password";
$this->link = mysql_connect($this->host, $this->user, $this->pass) or die("<br>Could not connect 1: " . mysql_error());
mysql_select_db($this->db);
}
function query($query) {
$result = mysql_query($query, $this->link) or die ("<br>Could not execute command 1: ".mysql_error());
return $result;
}
function thislink() {
return $this->link;
}
function close() {
mysql_close($this->link);
}
}
How to change it into PDO or mysqli so the wamp could use it

Answer 1

You can't.
Your class is not a black box, you have for example a public method that returns the MySQL link identifier:
function thislink() {
return $this->link;
}
If you change that to another database interface, you will run into problems when you call this method as it will not contain what the calling end is expecting.
The same applies to your public query() method:
function query($query) {
$result = mysql_query($query, $this->link) or die ("<br>Could not execute command 1: ".mysql_error());
return $result;
}
That returns a mysql resource in case of for example a SELECT statement so if you change that to msyqli or PDO, the calling side will not be able to handle it.

Answer 2

class DB {
function DB() {
$this->host = "localhost";
$this->db = "dbtest";
$this->user = "root" ;
$this->pass = "password";
$this->link = new PDO("mysql:host=$this->host;dbname=$this->db", $this->user, $this->pass);
}
function query($query) {
$result = $this->link->query($query);
return $result;
}
function thislink() {
return $this->link;
}
function close() {
$this->link = NULL;
}
}

Answer 3

Your class should look something like this:
Note that I change the constructor to __construct(), since in PHP 7 the other way what you used will be deprecated. Also I put the variables as arguments in the constructor with default values. I also enabled error mode for your PDO connection, only have it on in testing!, never in production.
<?php
class DB {
public $host;
public $db;
public $user;
public $pass;
private $link;
public function __construct($host = "localhost", $db = "dbtest", $user = "root", $pass = "password") {
$this->host = $host;
$this->db = $db;
$this->user = $user;
$this->pass = $pass;
try {
$this->link = new PDO("mysql:host={$this->host};dbname={$this->db}", $this->user, $this->pass);
$this->link->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
} catch(PDOExcpetion $e) {
echo $e->getMessage();
}
}
function query($query) {
$stmt = $this->link->prepare($query);
$stmt->execute();
return $stmt;
}
function thislink() {
return $this->link;
}
function close() {
$this->link = null;
}
}
?>
For more information about PDO see the manual: http://php.net/manual/en/book.pdo.php
You may also want to take a look into prepared statements.